PHOSPHATIDYL-3,4.5-TRIPHOSPHATE-DEPENDENT PROTEIN KINASE

Abstract: A substantially pure 3-phosphoinositide dependent protein kinase that phosphorylates and activates protein kinase B alpha . A recombinant polynucleotide encoding a protein kinase as defined. Uses of the protein kinase and polynucleotide, especially in screening for new drugs.

Description: PHOSPHATIDYL-3.4.5-TRIPHOSPHATE-DEPENDENT PROTEIN KINASE The present invention relates to enzymes, to poly nucleotides encoding enzymes and to uses of enzymes and poly nucleotides. Protein kinase B (PKB) [1] or RAC protein kinase [2] is the cellular homologue of a viral oncogene v-Akt [3] and has therefore also been termed c-Akt. The current interest in PKB stems firstly from the discovery that it is activated rapidly in response to insulin and growth factors and that the activation is prevented by inhibitors of phosphoinositide (PI) 3-kinase [4-6]; secondly, from the finding that PKB isoforms are overexpressed in a significant percentage of ovarian, pancreatic [7, 8] and breast cancer cells [2]. PKB appears to mediate the insulin-induced inhibition of glycogen synthase kinase-3 (GSK3) in L6 myotubes which is thought to underlie, at least in part, the insulin- induced dephosphorylation and activation of glycogen synthase [9] and protein synthesis initiation factor eIF2 [10] that contribute to the stimulation of glycogen and protein synthesis by insulin. However PϊCB is likely to have other physiological substrates and, in transfection based experiments, has been shown to activate p70 S6 kinase [5] , to stimulate the translocation of the glucose transporter GLUT4 to the plasma membrane and enhance glucose uptake into 3T3-L1 adipocytes [11], and to mediate me IGF 1 -induced survival of neurones [12] and fibroblasts [13] against apoptosis. A critical question concerns the mechanism by which PI 3-kinase triggers the activation of PKB. The activation of PKB is accompanied by its phosphorylation [5,14] and we recently showed that activation by insulin or IGF1 resulted from its phosphorylation at Thr-308 and Ser-473 [15] . Moreover, the insulin or IGF1 induced phosphorylation of both residues was abolished by wortmannin, an inhibitor of PI 3-kinase [15]. We believe that the protein kinases which phosphorylate PKB at Thr-308 and Ser-473 might themselves be activated by phosphatidylinositol 3,4,5 trisphosphate (PtdIns(3,4,5)P3), the product of the PI 3-kinase reaction. In the work presented here, we demonstrate that this is indeed the case, and we describe the purification and characterisation of a 3- phosphoinositide-dependent protein kinase (PDK1) which activates PKB and we disclose polynucleotides which encode PDK1 and uses for PDK1 and said polynucleotides. A first aspect of the invention provides a substantially pure 3- phosphoinositide dependent protein kinase that phosphorylates and activates protein kinase Bo.. By "substantially pure" we mean that the 3-phosphoinositide-dependent protein kinase is substantially free of other proteins. Thus, we include any composition mat includes at least 30% of the protein content by weight as the said 3-phosphoinositide-dependent protein kinase, preferably at least 50% , more preferably at least 70%, still more preferably at least 90% and most preferably at least 95 % of the protein content is the said 3- phosphoinositide-dependent protein kinase. Thus, the invention also includes compositions comprising the 3- phosphoinositide-dependent protein kinase and a contaminant wherein the contaminant comprises less than 70% of the composition by weight, preferably less than 50% of the composition, more preferably less than 30% of the composition, still more preferably less than 10% of the composition and most preferably less than 5 % of the composition by weight. The invention also includes the substantially pure said 3-phosphoinositide- dependent protein kinase when combined with other components ex vivo, said other components not being all of the components found in the cell in which said protein kinase is found. It is preferred that the substantially pure 3-phosphoinositide-dependent protein kinase is a substantially pure phosphatidyl-3,4-5-trisphosphate- dependent protein kinase or a substantially pure phosphatidyl-3,4- bisphosphate-dependent protein kinase. By "phosphorylates protein kinase Bα." we include the meaning that the 3-phosphoinositide-dependent protein kinase is able to transfer a phosphate group from ATP to an acceptor group of protein kinase Bo:. Preferably, the acceptor group is Thr-308. By "protein kinase Be." we include any protein kinase Be. or any suitable derivative or fragment thereof or fusion of protein kinase Bα- or derivative, or fragment thereof. For example, it is particularly preferred that the protein kinase Be- is a fusion between glutathione-S-transferase and protein kinase Bα. as described in Example 1 (GST-PKBα; see also reference 27). It is preferred that the PKBα- is a human PKBα.. It should be appreciated that the said 3-phosphoinositide-dependent protein kinase from one species or tissue can phosphorylate and activate PKBα from another species or tissue. By "activates protein kinase Bee" we include the meaning that upon phosphorylation by the said 3-phosphoinositide-dependent protein kinase the activity of protein kinase Bo- to a given substrate increases by at least ten-fold compared to the protein kinase Bo. which has not been so phosphorylated, preferably by at least 20-fold and more preferably by at least 30-fold. Suitably, the activity of protein kinase Bα is measured using the synthetic peptide RPRAATF (SEQ ID No 1). By "3-phosphoinositide-dependent protein kinase" we include the meaning that the protein kinase is substantially inactive at activating PKBα: in the absence of a suitable 3-phosphoinositide (or a compound that mimics the effect of a 3-phosphoinositide). In particular, the said protein kinase has at least ten-fold increased activity towards protein kinase Bα: in the presence of a 3-phosphoinositide compared to the activity in the absence of said 3-phosphoinositide, preferably at least 100-fold, more preferably at least 1000-fold, and still more preferably at least 10,000-fold. It will be appreciated that the 3 -phosphoinositide-dependent protein kinase may be activated by mimics of 3-phosphoinositide as described in more detail below. Preferably, the activation of PKBα: by the 3-phosphoinositide-dependent protein kinase is substantially accelerated by the D-enantiomer of sn-1- stearoyl-2-arachidonyl phosphatidylinositol 3,4,5-trisphosphate but is not substantially accelerated by the L-enantiomer of the said phosphatidylinositol 3 ,4,5-trisphosphate. Preferably, the activation of PKBc- by 3-phosphoinositide-dependent protein kinase is substantially activated by the D-enantiomer of sn-1 ,2- dipalmitoyl phosphatidylinositol 3,4,5-trisphosphate or -sn-l^-dipalmitoyl phosphatidylinositol 3,4-bisphosphate but is not substantially activated by the L-enantiomers of the said phosphatidylinositol phosphates. Preferably, the activation of protein kinase Bα by 3-phosphinositide- dependent protein kinase is not substantially activated by phosphatidylinositol 3,5-bisphosphate or phosphatidylinositol 4,5- bisphosphate or phosphatidylinositol 3-phosphate or inositol 1,3,4,5- tetrakisphosphate. Thus, particularly with reference to Figure 6 and the rabbit skeletal muscle PDKl of Example 1, the following 3-phosphoinositides have been found to activate the said 3-phosphoinositide-dependent kinase (in order of level of activation; most effective first): 1. Lipid 5: Racemic -yn-l,2-dilinoleoyl PtdIns(3,4,5)P 3 . 2. (Equal) Lipid 2: D-enantiomer of -sn-l-stearoyl-2-arachidonyl PtdIns(3,4,5)P 3 . 2. (Equal) Lipid 3: D-enantiomer of ,s?z-2-arachidonyl-3-stearoyl PtdIns(3,4,5)P 3 . 4. (Equal) Lipid 6: sn-1,2 di-palmitoyl PtdIns(3,4,5)P 3 . 4. Equal Lipid 7: sn-1 ,2 di-palmitoyl PtdIns(3,4)P 2 . The following phospholipids cause no significant activation, at least in relation to rabbit skeletal muscle PDKl : 6. Lipid 2: L-enantiomer of -s , n-l-stearoyl-2-arachidonyl PtdIns(3,4,5)P 3 . 7. Lipid 4: L-enantiomer of sn-2-arachidonyl-3-stearoyl PtdIns(3,4,5)P 3 . 8. Lipid 9: PtdIns(4,5)P 2 . 9. Lipid 8: sn-l,2 di-palmitoyl PtdIns(3,5)P 2 . 10. Lipid 11 : sn-1,2 di-palmitoyl Ptdlns-3P. 11. Lipid 10: Ptdlns 4P. 12. IP 4 : Ins(l,3,4,5P 4 . We have found mat the human PDKl enzyme has substantially the same lipid preference as described above. It is preferred if the 3-phosphoinositide-dependent protein kinase is substantially unaffected by wortmannin. It should be appreciated that the said 3 -phosphoinositide-dependent protein kinase that phosphorylate and activates protein kinase Bα: is likely to phosphorylate and activate other forms of protein kinase B such as protein kinase Bβ and protein kinase B7. We have shown that PDKl phosphorylates and activates not only PKBα: but also PKBβ and PKBγ. A protein kinase B 3 is described in reference 7. A protein kinase Bγ is described in Konishi et al (1995) Biochem. Biophys. Res. Comm. 216, 526-534. The 3 -phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα: may be isolated from any convenient tissue and from any mammal as described below. It is believed that isoforms of the enzyme exist in different tissues within the same mammal and that the invention encompasses said isoforms and said 3-phosphoinositide- dependent protein kinases from any mammal. It is preferred that the said 3-phosphoinositide-dependent protein kinase is the human said enzyme. It is also preferred if it is the rabbit said enzyme. It is preferred if the said 3-phosphoinositide-dependent protein kinase is about 67 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). A particularly preferred embodiment is a substantially pure 3- phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα: the 3-phosphoinositide-dependent protein kinase comprising the amino acid sequences ANSFNGTAQYNSPELL or AGΝEYLIFQK or LDHPFFVK or two or more of these sequences or amino sequences with from 1 to 4 conservative substitutions thereof. What is meant by "conservative substitutions" is described below. A particular preferred embodiment is a polypeptide which comprises the amino acid sequence (SEQ ID No 2) MARTTΞQLYDAVPIQSSWLCSCPSPSMWTQTESΞTPPGIPGGSRQGPA DGTAAEPRPGAGS LQHAQPPPQPRKKRPEDFKFGKILGEGSFSTWLARELATSREYAIKILEKRHIIKENKVPYVT RERDVMSRLDHPFFVKLYFTFQDDEKLYFGLSYAKNGELLKYIRKIGSFDETCTRFYTAEIVSA LEYLHGKGIIHRDL PENILLNEDMHIQITDFGTAKVLSPESKQARANSFVGTAQYVSPELLTE KSACKSSDLWALGCIIYQLVAGLPPFRAGNEYLIFQKIIKLEYDFPEKFFPKARDLVEKLLVLD ATKRLGCEEMEGYGPLKAHPFFESVT ENLHQQTPPKLTAYLPAMΞEDDEDCYGNYDNLLSQFG CMQVSSSSSSHSLSASDTGLPQRSGSNIEQYIHDLDSNSFELDLQFSEDEKRLLLEKQAGGNPW HQFVENN I KMGPVDKR GLFARRRQLLLTEGPHLYYVDPV KVLKGEIPWSQELRPEAKNFK TFFVHTP RTYYLMDPSGNAHKWCRKIQEV RQRYQSHPDAAVQ or a variant, fragment, derivative or fusion thereof. The amino acid sequence is that of human PDKl as determined from the nucleotide sequence of cDNAs encoding human PDKl. The deduced amino acid sequence is also given in Figure 10. As is discussed in more detail in the Examples, at least in relation to human PDKl, experiments in which the pleckstrin homology (PH) domains (which have been found to be present in human PDKl and which are known to be present in PKBα: and are believed to be involved in binding phospholipids) of either PDKl or PKBα: were deleted indicated that the binding of PtdIns(3,4,5)P3 or PtdIns(3,4)P2 to PKBα: is required for phosphorylation and activation by PDKl . A GST-PKBα: mutant lacking the PH domain possesses a 3-fold higher activity than that of full length wild-type GST-PKBα and was activated and phosphorylated by PDKl in a PtdIns(3,4,5)P3 independent manner; however, the rate of activation was reduced about 20-fold compared to wild-type GST-PKBα. A mutant PDKl lacking the putative C-terminal PH domain, expressed as a GST-fusion protein, is still able to activate GST-PKBα: in a PtdIns(3,4,5)P3-dependent manner, but the rate of activation was reduced about 30-fold compared to full length GST-PDK1. The effect of PtdIns(3,4,5)P3/PtdIns(3,4)P2 in the activation of PKBc- by PDKl is, therefore, at least partly substrate directed. However, the drastic reduction in the rate of activation of PKB by PDKl when the PH domain of PDKl is deleted indicates the importance of the PH domain of PDKl and hence the importance of PtdIns(3,4,5)P3/PtdIns(3,4)P2 in the activation of PKB by PDKl . Thus, the substantially pure 3- phosphoinositide dependent protein kinase that phosphorylates and activates protein kinase Bo: may be 3-phosphoinositide dependent in the sense that the intact enzyme (for example intact PDKl) requires the presence of a 3-phosphoinositide in order to phosphorylate an intact PKBα in vivo. The protein kinase of the invention phosphorylates and activates PKBα in a 3-phosphoinositide-dependent manner. PDKl has been shown by us to phosphorylate p70 S6 kinase in the absence of InsPtd(3,4,5)P3. PDKl has been shown to bind PtdIns(3,4,5)P3 directly. A second aspect of the invention provides a recombinant polynucleotide encoding a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα provided that the recombinant polynucleotide is not the DNA corresponding to IMAGE clone 526583 or IMAGE clone 626511. The DNA sequence of at least part of the inserts of these clones are given in GenBank Accession No AA121994 and AA186323, respectively. Preferences for the said 3- phosphoinositide-dependent protein kinase are the same as in the first aspect of the invention. The invention also encompasses polynucleotides which encode variants, fragments, derivatives or fusions of said 3- phosphoinositide-dependent protein kinase or fusions of the said variants, fragments or derivatives. The EST AA121994 was derived from pancreas tissue and the EST AA186323 was derived from HeLa cells. A particular preferred embodiment of the invention is a polynucleotide comprising the nucleotide sequence (SEQ ID No 3) ATGGCCAGGACCACCAGCCAGCTGTATGACGCCGTGCCCATCCAGTCCAGCGTGGTGTTA TGTTCCTGCCCATCCCCATCAATGGTGAGGACCCAGACTGAGTCCAGCACGCCCCCTGGC ATTCCTGGTGGCAGCAGGCAGGGCCCCGCCATGGACGGCACTGCAGCCGAGCCTCGGCCC GGCGCCGGCTCCCTGCAGCATCCCAGCCTCCGCCGCAGCCTCGGAAGAAGCGGCCTGAGG ACTTCAAGTTTGGGAAAATCCTTGGGGAAGGCTCTTTTTCCACGGTTGTCCTGGCTCGAG AACTGGCAACCTCCAGAGAATATGCGATTAAAATTCTGGAGAAGCGACATATCATAAAAG AGAACAAGGTCCCCTATGTAACCAGAGAGCGGGATGTCATGTCGCGCCTGGATCACCCCT TCTTTGTTAAGCTTTACTTCACATTTCAGGACGACGAGAAGCTGTATTTCGGCCTTAGTT ATGCCAAAAATGGAGAACTACTTAAATATATTCGCAAAATCGGTTCATTCGATGAGACCT GTACCCGATTTTACACGGCTGAGATCGTGTCTGCTTTAGAGTACTTGCACGGCAAGGGCA TCATTCACAGGGACCTTAAACCGGAAAACATTTTGTTAAATGAAGATATGCACATCCAGA TCACAGATTTTGGAACAGCAAAAGTCTTATCCCCAGAGAGCAAACAAGCCAGGGCCAACT CATTCGTGGGAACAGCGCAGTACGTTTCTCCAGAGCTGCTCACGGAGAAGTCCGCCTGTA AGAGTTCAGACCTTTGGGCTCTTGGATGCATAATATACCAGCTTGTGGCAGGACTCCCAC CATTCCGAGCTGGAAACGAGTATCTTATATTTCAGAAGATCATTAAGTTGGAATATGACT TTCCAGAAAAATTCTTCCCTAAGGCAAGAGACCTCGTGGAGAAACTTTTGGTTTTAGATG CCACAAAGCGGTTAGGCTGTGAGGAAATGGAAGGATACGGACCTCTTAAAGCACACCCGT TCTTCGAGTCCGTCACGTGGGAGAACCTGCACCAGCAGACGCCTCCGAAGCTCACCGCTT ACCTGCCGGCTATGTCGGAAGACGACGAGGACTGCTATGGCAATTATGACAATCTCCTGA GCCAGTTTGGCTGCATGCAGGTGTCTTCGTCCTCCTCCTCACACTCCCTGTCAGCCTCCG ACACGGGCCTGCCCCAGAGGTCAGGCAGCAACATAGAGCAGTACATTCACGATCTGGACT CGAACTCCTTTGAACTGGACTTACAGTTTTCCGAAGATGAGAAGAGGTTGTTGTTGGAGA AGCAGGCTGGCGGAAACCCTTGGCACCAGTTTGTAGAAAATAATTTAATACTAAAGATGG GCCCAGTGGATAAGCGGAAGGGTTTATTTGCAAGACGACGACAGCTGTTGCTCACAGAAG GACCACATTTATATTATGTGGATCCTGTCAACAAAGTTCTGAAAGGTGAAATTCCTTGGT CACAAGAACTTCGACCAGAGGCCAAGAATTTTAAAACTTTCTTTGTCCACACGCCTAACA GGACGTATTATCTGATGGACCCCAGCGGGAACGCACACAAGTGGTGCAGGAAGATCCAGG AGGTTTGGAGGCAGCGATACCAGAGCCACCCGGACGCCGCTGTGCAGTGA or variants or variations thereof. The given nucleotide sequence is that containing a coding sequence which encodes human PDKl . The cDNA sequence is also given in Figure 10. IMAGE clones 526583 and 626511 are known in the art and are publicly available from HGMP Resource Centre, I.M.A.G.E. Consortium, Hinxton, Cambridge CB1 1SB, UK. The clones are partial length cDNAs inserted into pBluescript SK-. It was not known that these clones were derived from a mRNA encoding a protein kinase. Certain other ESTs are publicly available which encode parts of the PDKl cDNA namely H97903 (melanocyte), AAO 18098 (retina), AA 18097 (retina), AA019394 (retina), AA019393 (retina, N22904 (melanocyte), W94736 (fetal heart), EST 51985 (gall bladder), N31292 (melanocyte), AA188174 (HeLa cells), AA100210 (colon) and R84271 (retina). The polynucleotides corresponding to these ESTs are not claimed per se but they may be useful in carrying out certain parts of the invention. It had not been shown that these clones were derived from a mRNA encoding a protein kinase. The invention also includes a polynucleotide comprising a fragment of the recombinant polynucleotide of the second aspect of the invention. Preferably, the polynucleotide comprises a fragment which is at least 10 nucleotides in length, more preferably at least 14 nucleotides in length and still more preferably at least 18 nucleotides in length. Such polynucleotides are useful as PCR primers. The polynucleotide or recombinant polynucleotide may be DNA or RNA, preferably DNA. The polynucleotide may or may not contain introns in the coding sequence; preferably the polynucleotide is a cDNA. A "variation" of the polynucleotide includes one which is (i) usable to produce a protein or a fragment thereof which is in turn usable to prepare antibodies which specifically bind to the protein encoded by the said polynucleotide or (ii) an antisense sequence corresponding to the gene or to a variation of type (i) as just defined. For example, different codons can be substituted which code for the same amino acid(s) as the original codons. Alternatively, the substitute codons may code for a different amino acid that will not affect the activity or immunogenicity of the protein or which may improve or otherwise modulate its activity or immunogenicity. For example, site-directed mutagenesis or other techniques can be employed to create single or multiple mutations, such as replacements, insertions, deletions, and transpositions, as described in Botstein and Shortle, "Strategies and Applications of In Vitro Mutagenesis," Science, 229: 193-210 (1985), which is incorporated herein by reference. Since such modified polynucleotides can be obtained by the application of known techniques to the teachings contained herein, such modified polynucleotides are within the scope of the claimed invention. Moreover, it will be recognised by those skilled in the art that the polynucleotide sequence (or fragments thereof) of the invention can be used to obtain other polynucleotide sequences that hybridise with it under conditions of high stringency. Such polynucleotides includes any genomic DNA. Accordingly, the polynucleotide of the invention includes polynucleotide mat shows at least 55 per cent, preferably 60 per cent, and more preferably at least 70 per cent and most preferably at least 90 per cent homology with the polynucleotide identified in the method of the invention, provided that such homologous polynucleotide encodes a polypeptide which is usable in at least some of the methods described below or is otherwise useful. Per cent homology can be determined by, for example, the GAP program of the University of Wisconsin Genetic Computer Group. DNA-DNA, DNA-RNA and RNA-RNA hybridisation may be performed in aqueous solution containing between 0.1XSSC and 6XSSC and at temperatures of between 55 °C and 70°C. It is well known in the art that the higher the temperamre or the lower the SSC concentration the more stringent the hybridisation conditions. By "high stringency" we mean 2XSSC and 65°C. 1XSSC is 0.15M NaCl/0.015M sodium citrate. Polynucleotides which hybridise at high stringency are included within the scope of the claimed invention. "Variations" of the polynucleotide also include polynucleotide in which relatively short stretches (for example 20 to 50 nucleotides) have a high degree of homology (at least 80% and preferably at least 90 or 95%) with equivalent stretches of the polynucleotide of the invention even though the overall homology between the two polynucleotides may be much less. This is because important active or binding sites may be shared even when the general architecture of the protein is different. By "variants" of the polypeptide we include insertions, deletions and substimtions, either conservative or non-conservative, where such changes do not substantially alter the activity of the said 3-phosphoinositide- dependent protein kinase. By "conservative substimtions" is intended combinations such as Gly, Ala; Val, He, Leu; Asp, Glu; Asn, Gin; Ser, Thr; Lys, Arg; and Phe, Tyr. Such variants may be made using the methods of protein engineering and site-directed mutagenesis well known in the art. Preferably, the variant or variation of the polynucleotide encodes a 3- phosphoinositide-dependent protein kinase that has at least 30% , preferably at least 50% and more preferably at least 70% of the activity towards protein kinase Bα of a natural said 3-phosphoinositide-dependent protein kinase, under the same assay conditions. By "fragment of said 3 -phosphoinositide-dependent protein kinase" we include any fragment which retains activity or which is useful in some other way, for example, for use in raising antibodies or in a binding assay. By "fusion of said 3 -phosphoinositide-dependent protein kinase" we include said protein kinase fused to any other polypeptide. For example, the said protein kinase may be fused to a polypeptide such as glutathione- S-transferase (GST) or protein A in order to facilitate purification of said protein kinase. Fusions to any variant, fragment or derivative of said protein kinase are also included in the scope of the invention. A further aspect of the invention provides a replicable vector comprising a recombinant polynucleotide encoding a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα, or a variant, fragment, derivative or fusion of said protein kinase or a fusion of said variant, fragment or derivative. A variety of methods have been developed to operably link polynucleotides, especially DNA, to vectors for example via complementary cohesive te-rmini. For instance, complementary homopolymer tracts can be added to the DNA segment to be inserted to the vector DNA. The vector and DNA segment are then joined by hydrogen bonding between the complementary homopolymeric tails to form recombinant DNA molecules. Synthetic linkers containing one or more restriction sites provide an alternative method of joining the DNA segment to vectors. The DNA segment, generated by endonuclease restriction digestion as described earlier, is treated with bacteriophage T4 DNA polymerase or E. coli DNA polymerase I, enzymes that remove protruding, 3 '-single-stranded termini with their 3'-5'-exonucleolytic activities, and fill in recessed 3 '-ends with their polymerizing activities. The combination of these activities therefore generates blunt-ended DNA segments. The blunt-ended segments are then incubated with a large molar excess of linker molecules in the presence of an enzyme that is able to catalyze the ligation of blunt-ended DNA molecules, such as bacteriophage T4 DNA ligase. Thus, the products of the reaction are DNA segments carrying polymeric linker sequences at their ends. These DNA segments are then cleaved with the appropriate restriction enzyme and ligated to an expression vector that has been cleaved with an enzyme that produces termini compatible with those of the DNA segment. Synthetic linkers containing a variety of restriction endonuclease sites are commercially available from a number of sources including International Biotechnologies Inc, New Haven, CN, USA. A desirable way to modify d e DNA encoding the polypeptide of the invention is to use the polymerase chain reaction as disclosed by Saiki et al (1988) Science 239, 487-491. This method may be used for introducing the DNA into a suitable vector, for example by engineering in suitable restriction sites, or it may be used to modify the DNA in other useful ways as is known in the art. In this method the DNA to be enzymatically amplified is flanked by two specific primers which themselves become incorporated into the amplified DNA. The said specific primers may contain restriction endonuclease recognition sites which can be used for cloning into expression vectors using methods known in the art. The DNA (or in the case of retroviral vectors, RNA) is then expressed in a suitable host to produce a polypeptide comprising the compound of the invention. Thus, the DNA encoding the polypeptide constituting the compound of the invention may be used in accordance with known techniques, appropriately modified in view of the teachings contained herein, to construct an expression vector, which is then used to transform an appropriate host cell for the expression and production of the polypeptide of the invention. Such techniques include those disclosed in US Patent Nos. 4,440,859 issued 3 April 1984 to Rutter et al, 4,530,901 issued 23 July 1985 to Weissman, 4,582,800 issued 15 April 1986 to Crowl, 4,677,063 issued 30 June 1987 to Mark et al, 4,678,751 issued 7 July 1987 to Goeddel, 4,704,362 issued 3 November 1987 to Itakura et al, 4,710,463 issued 1 December 1987 to Murray, 4,757,006 issued 12 July 1988 to Toole, Jr. et al, 4,766,075 issued 23 August 1988 to Goeddel et al and 4,810,648 issued 7 March 1989 to Stalker, all of which are incorporated herein by reference. The DNA (or in the case of retroviral vectors, RNA) encoding the polypeptide constituting the compound of me invention may be joined to a wide variety of other DNA sequences for introduction into an appropriate host. The companion DNA will depend upon the nature of the host, the manner of the introduction of the DNA into the host, and whether episomal maintenance or integration is desired. Generally, the DNA is inserted into an expression vector, such as a plasmid, in proper orientation and correct reading frame for expression. If necessary, the DNA may be linked to the appropriate transcriptional and translational regulatory control nucleotide sequences recognised by the desired host, although such controls are generally available in the expression vector. The vector is then introduced into the host through standard techniques. Generally, not all of the hosts will be transformed by the vector. Therefore, it will be necessary to select for transformed host cells. One selection technique involves incorporating into the expression vector a DNA sequence, with any necessary control elements, that codes for a selectable trait in the transformed cell, such as antibiotic resistance. Alternatively, the gene for such selectable trait can be on another vector, which is used to co-transform the desired host cell. Host cells that have been transformed by the recombinant DNA of the invention are then culmred for a sufficient time and under appropriate conditions known to those skilled in the art in view of the teachings disclosed herein to permit the expression of the polypeptide, which can then be recovered. Many expression systems are known, including bacteria (for example E. coli and Bacillus subtilis), yeasts (for example Saccharomyces cerevisiae), filamentous fungi (for example Aspergillus), plant cells, animal cells and insect cells. The vectors include a prokaryotic replicon, such as the ColEl on, for propagation in a prokaryote, even if the vector is to be used for expression in other, non-prokaryotic, cell types. The vectors can also include an appropriate promoter such as a prokaryotic promoter capable of directing the expression (transcription and translation) of the genes in a bacterial host cell, such as E. coli, transformed therewith. A promoter is an expression control element formed by a DNA sequence that permits binding of RNA polymerase and transcription to occur. Promoter sequences compatible with exemplary bacterial hosts are typically provided in plasmid vectors containing convenient restriction sites for insertion of a DNA segment of the present invention. Typical prokaryotic vector plasmids are pUC18, pUC19, pBR322 and pBR329 available from Biorad Laboratories, (Richmond, CA, USA) and p7Vc99A and pKK223-3 available from Pharmacia, Piscataway, NJ, USA. A typical mammalian cell vector plasmid is pSNL available from Pharmacia, Piscataway, ΝJ, USA. This vector uses the SV40 late promoter to drive expression of cloned genes, the highest level of expression being found in T antigen-producing cells, such as COS-1 cells. An example of an inducible mammalian expression vector is pMSG, also available from Pharmacia. This vector uses the glucocorticoid-inducible promoter of the mouse mammary tumour virus long terminal repeat to drive expression of the cloned gene. Useful yeast plasmid vectors are pRS403-406 and pRS413-416 and are generally available from Stratagene Cloning Systems, La Jolla, CA 92037, USA. Plasmids pRS403, pRS404, pRS405 and pRS406 are Yeast Integrating plasmids (Yips) and incorporate the yeast selectable markers HIS3, TRP1, LEU2 and URA3. Plasmids pRS413-416 are Yeast Centromere plasmids (YCps). The present invention also relates to a host cell transformed with a polynucleotide vector construct of the present invention. The host cell can be either prokaryotic or eukaryotic. Bacterial cells are preferred prokaryotic host cells and typically are a strain of E. coli such as, for example, the E. coli strains DH5 available from Bethesda Research Laboratories Inc., Bethesda, MD, USA, and RR1 available from the American Type Culture Collection (ATCC) of Rockville, MD, USA (No ATCC 31343). Preferred eukaryotic host cells include yeast, insect and mammalian cells, preferably vertebrate cells such as those from a mouse, rat, monkey or human fibroblastic and kidney cell lines. Yeast host cells include YPH499, YPH500 and YPH501 which are generally available from Stratagene Cloning Systems, La Jolla, CA 92037, USA. Preferred mammalian host cells include Chinese hamster ovary (CHO) cells available from the ATCC as CCL61, NIH Swiss mouse embryo cells NIH/3T3 available from the ATCC as CRL 1658, monkey kidney-derived COS-1 cells available from the ATCC as CRL 1650 and 293 cells which are human embryonic kidney cells. Preferred insect cells are Sf9 cells which can be transfected with baculovirus expression vectors. Transformation of appropriate cell hosts with a DNA construct of the present invention is accomplished by well known methods mat typically depend on the type of vector used. With regard to transformation of prokaryotic host cells, see, for example, Cohen et al (1972) Proc. Natl. Acad. Sci. USA 69, 2110 and Sambrook et al (1989) Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY. Transformation of yeast cells is described in Sherman et al (1986) Methods In Yeast Genetics, A Laboratory Manual, Cold Spring Harbor, NY. The method of Beggs (1978) Nature 275, 104-109 is also useful. With regard to vertebrate cells, reagents useful in transfecting such cells, for example calcium phosphate and DEAE-dextran or liposome formulations, are available from Stratagene Cloning Systems, or Life Technologies Inc., Gaithersburg, MD 20877, USA. Electroporation is also useful for transforming and/or transfecting cells and is well known in the art for transforming yeast cell, bacterial cells, insect cells and vertebrate cells. For example, many bacterial species may be transformed by the methods described in Luchansky et al (1988) Mol. Microbiol. 2, 637-646 incorporated herein by reference. The greatest number of transformants is consistently recovered following electroporation of the DNA-cell mixture suspended in 2.5X PEB using 6250V per cm at 25μFD. Methods for transformation of yeast by electroporation are disclosed in Becker & Guarente (1990) Methods Enzymol. 194, 182. Successfully transformed cells, ie cells that contain a DNA construct of the present invention, can be identified by well known techniques. For example, cells resulting from the introduction of an expression construct of the present invention can be grown to produce die polypeptide of the invention. Cells can be harvested and lysed and their DNA content examined for the presence of the DNA using a method such as mat described by Southern (1975) J. Mol. Biol. 98, 503 or Berent et al (1985) Biotech. 3, 208. Alternatively, the presence of the protein in the supernatant can be detected using antibodies as described below. In addition to directly assaying for the presence of recombinant DNA, successful transformation can be confirmed by well known immunological methods when the recombinant DNA is capable of directing the expression of the protein. For example, cells successfully transformed with an expression vector produce proteins displaying appropriate antigenicity. Samples of cells suspected of being transformed are harvested and assayed for the protein using suitable antibodies. Thus, in addition to me transformed host cells themselves, the present invention also contemplates a culture of those cells, preferably a monoclonal (clonally homogeneous) culture, or a culture derived from a monoclonal culture, in a nutrient medium. A further aspect of the invention provides a method of making a 3- phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα or a variant, derivative, fragment or fusion thereof or a fusion of a variant, fragment or derivative the method comprising culturing a host cell comprising a recombinant polynucleotide or a replicable vector which encodes said 3-phosphoinositide-dependent protein kinase, and isolating said protein kinase or a variant, derivative, fragment or fusion thereof of a fusion of a variant, fragment or derivative from said host cell. Methods of cultivating host cells and isolating recombinant proteins are well known in the art. A still further aspect of the invention provides a method of isolating a 3- phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα the method comprising me steps of (a) obtaining tissue from a mammal that contains said 3-phosphoinositide- dependent kinase, (b) obtaining a cell-free extract from said tissue, (c) fractionating said cell-free extract and (d) selecting a fraction from step (c) which is capable of phosphorylating and activating protein kinase Bα in the presence of a 3-phosphoinositide. Preferably, the 3-phosphoinositide is any of the preferred 3- phosphoinositides as disclosed in relation to the first aspect of the invention; most preferably it is phosphatidylinositol-3 ,4,5-trisphosphate or phosphatidylinositol-3,4-bisphosphate. Preferably, further steps are employed. Conveniently, in a step (e) the fraction of step (d) is fractionated further and in a step (f) a fraction is selected from step (e) which is capable of phosphorylating and activating protein kinase Bα in the presence of a 3-phosphoinositide. Steps (e) and (f) may be repeated until a substantially pure preparation of a 3 -phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα is obtained. Suitably, the fractionation steps include any of ion exchange chromatography, polyethylene glycol (PEG) precipitation, heparin chromatography or any other fractionation procedures. Preferably, the method steps are those substantially as described in Example 1. Conveniently, the tissue is skeletal muscle. The tissue may be from any mammal including humans. A further aspect of the invention provides a phosphoinositide-dependent protein kinase which can phosphorylate and activate protein kinase Bα, or a variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative obtainable by the methods herein disclosed. A still further aspect of the invention provides an antibody reactive towards a phosphoinositide-dependent protein kinase of the invention. Antibodies reactive towards the said phosphoinositide-dependent protein kinase of the invention may be made by methods well known in the art. In particular, the antibodies may be polyclonal or monoclonal. Suitable monoclonal antibodies which are reactive towards the said protein kinase may be prepared by known techniques, for example those disclosed in " Monoclonal Antibodies: A manual of techniques' ' ' , H Zola (CRC Press, 1988) and in "Monoclonal Hybridoma Antibodies: Techniques and Applications", SGR Hurrell (CRC Press, 1982). In a preferred embodiment the antibody is raised using any one of the peptide sequences ANSFVGTAQYVSPELL (SEQ ID No 4) or AGNEYLIFQK (SEQ ID No 5) or LDHPFFVK (SEQ ID No 6). It is preferred if polyclonal antipeptide antibodies are made. Other peptides may be used to make antibodies, for example the peptides RQRYQSHPDAAVQ (SEQ ID No 7) and LSPESKQARANS (SEQ ID No 8). Peptides in which one or more of the amino acid residues are chemically modified, before or after the peptide is syndiesised, may be used providing that the function of the peptide, namely the production of specific antibodies in vivo, remains substantially unchanged. Such modifications include forming salts with acids or bases, especially physiologically acceptable organic or inorganic acids and bases, forming an ester or amide of a terminal carboxyl group, and attaching amino acid protecting groups such as N-t-butoxycarbonyl. Such modifications may protect the peptide from in vivo metabolism. The peptides may be present as single copies or as multiples, for example tandem repeats. Such tandem or multiple repeats may be sufficiently antigenic themselves to obviate the use of a carrier. It may be advantageous for the peptide to be formed as a loop, with the N-terminal and C-terminal ends joined together, or to add one or more Cys residues to an end to increase antigenicity and/or to allow disulphide bonds to be formed. If the peptide is covalently linked to a carrier, preferably a polypeptide, then the arrangement is preferably such that the peptide of the invention forms a loop. According to current immunological theories, a carrier function should be present in any immunogenic formulation in order to stimulate, or enhance stimulation of, the immune system. It is thought that the best carriers embody (or, together with the antigen, create) a T-cell epitope. The peptides may be associated, for example by cross-linking, with a separate carrier, such as serum albumins, myoglobins, bacterial toxoids and keyhole limpet haemocyanin. More recently developed carriers which induce T-cell help in the immune response include the hepatitis-B core antigen (also called the nucleocapsid protein), presumed T-cell epitopes such as Thr-Ala-Ser-Gly-Val-Ala-Glu-Thr-Thr-Asn-Cys (SEQ ID No 9), beta-galactosidase and die 163-171 peptide of interleukin-1. The latter compound may variously be regarded as a carrier or as an adjuvant or as both. Alternatively, several copies of the same or different peptides of the invention may be cross-linked to one another; in this situation diere is no separate carrier as such, but a carrier function may be provided by such cross-linking. Suitable cross-linking agents include tihose listed as such in the Sigma and Pierce catalogues, for example glutaraldehyde, carbodiimide and succinimidyl 4-(N-maleimidomethyl)cyclohexane-l- carboxylate, the latter agent exploiting the -SH group on the C-terminal cysteine residue (if present). If the peptide is prepared by expression of a suitable nucleotide sequence in a suitable host, then it may be advantageous to express the peptide as a fusion product with a peptide sequence which acts as a carrier. Kabigen's "Ecosec" system is an example of such an arrangement. The peptide of the invention may be linked to other antigens to provide a dual effect. Peptides may be synthesised by the Fmoc-polyamide mode of solid-phase peptide synthesis as disclosed by Lu et al (1981) J. Org. Chem. 46, 3433 and references therein. Temporary N-amino group protection is afforded by the 9-fluorenylmethyloxycarbonyl (Fmoc) group. Repetitive cleavage of this highly base-labile protecting group is effected using 20% piperidine in N,N-dimethylformamide. Side-chain functionalities may be protected as their butyl ethers (in the case of serine threonine and tyrosine), butyl esters (in the case of glutamic acid and aspartic acid), butyloxycarbonyl derivative (in the case of ly sine and histidine), trityl derivative (in the case of cy steine) and 4-methoxy-2 , 3 , 6-trimethylbenzenesulphonyl derivative (in the case of arginine). Where glutamine or asparagine are C-terminal residues, use is made of he 4,4'-dimethoxybenzhydryl group for protection of the side chain amido functionalities. The solid-phase support is based on a polydimethyl-acrylamide polymer constituted from the three monomers dimethylacrylamide (backbone-monomer), bisacryloylethylene diamine (cross linker) and acryloylsarcosine methyl ester (functionalising agent). The peptide-to-resin cleavable linked agent used is the acid-labile 4-hydroxymethyl-phenoxy acetic acid derivative. All amino acid derivatives are added as their preformed symmetrical anhydride derivatives with the exception of asparagine and glutamine, which are added using a reversedN , N-dicyclohexy 1-carbodiimide/ 1 -hydroxybenzotriazolemediated coupling procedure. All coupling and deprotection reactions are monitored using ninhydrin, trinitrobenzene sulphonic acid or isotin test procedures. Upon completion of synthesis, peptides are cleaved from the resin support with concomitant removal of side-chain protecting groups by treatment with 95% trifluoroacetic acid containing a 50% scavenger mix. Scavengers commonly used are emanedithiol, phenol, anisole and water, me exact choice depending on me constituent amino acids of the peptide being synthesised. Trifluoroacetic acid is removed by evaporation in vacuo, with subsequent trituration with dieώyl ether affording the crude peptide. Any scavengers present are removed by a simple extraction procedure which on lyophilisation of the aqueous phase affords the crude peptide free of scavengers. Reagents for peptide synthesis are generally available from Calbiochem-Novabiochem (UK) Ltd, Nottingham NG7 2QJ, UK. Purification may be effected by any one, or a combination of, techniques such as size exclusion chromatography, ion-exchange chromatography and (principally) reverse-phase high performance liquid chromatography. Analysis of peptides may be carried out using thin layer chromatography, reverse-phase high performance liquid chromatography, amino-acid analysis after acid hydrolysis and by fast atom bombardment (FAB) mass spectrometric analysis. A further aspect of the invention provides a method of identifying a compound mat modulates the activity of a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα, the method comprising contacting a compound with the said 3- phosphoinositide-dependent protein kinase or a variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative thereof and determining whether, in the presence of said compound, phosphorylation and activation of a protein kinase B or phosphorylation a suitable substrate of the 3 -phosphoinositide-dependent protein kinase is changed compared to the activity of said 3-phosphoinositide-dependent protein kinase or said variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative thereof in the absence of said compound. We believe that the said 3-phosphoinositide-dependent protein kinase of the invention is able to phosphorylate not only protein kinase Bα but also other forms of protein kinase B such as protein kinase Bβ and protein kinase Bγ. We have shown that PDKl is able to phosphorylate PKBα, PKB/3 and PKBγ. Thus, in this method and me methods described below the protein kinase B can be any protein kinase B such as protein kinase Bα or protein kinase Bβ or protein kinase Bγ. Other substrates of the 3- phosphoinositide-dependent protein kinase may be used in the assay method of the invention, for example p70 S6 kinase. A suitable phospholipid such as PtdIns(3,4,5)P3 is typically present in the screen when a PKB containing a PH domain is used as a substrate but it is not necessary for a 3-phosphoinositide to be present in some circumstances, for example when p70 S6 kinase, or PKB lacking a PH domain, is used as a substrate. Phosphorylation of p70 S6 kinase occurs in the absence of PtdIns(3,4,5)P3. It will be appreciated that the method can be carried out in vitro using 3- phosphoinositide-dependent protein kinase or a variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative in the presence of a suitable protein kinase B or other suitable substrate. But it will also be appreciated that it may be carried out in vivo, for example using the yeast two-hybrid system to detect compounds which reduce or enhance the interactions between the phosphoinositide-dependent protein kinase and PKB or another suitable substrate. In one embodiment me compound decreases the activity of the 3- phosphoinositide-dependent protein kinase. In another embodiment the compound increases the activity of the 3- phosphoinositide-dependent protein kinase. Preferably the compound competes with 3-phosphoinositide. Preferably, the compound substantially reduces activation by phosphatidylinositol-3,4,5-trisphosphate or phosphatidyl-inositol-3,4-bisphosphate. Preferably, the compound substantially enhances activation by phosphatidylinositol-3,4,5- trisphosphate or phosphatidylinositol-3,4-bisphosphate. It will be appreciated diat the method may be used to identify compounds which bind to and effect me activity of either the said 3-phosphoinositide- dependent protein kinase or the protein kinase B when protein kinase B is present in the assay. A still further aspect of the invention provides a method of identifying a compound that mimics the effect of a 3-phosphoinositide on a 3- phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα, the method comprising determining whether said compound activates a said 3-phosphoinositide-dependent protein kinase or a suitable variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative so mat it can phosphorylate and activate protein kinase Bα or phosphorylate any other suitable substrate, the activation by said compound being in me absence of a 3- phosphoinositide. The activity of protein kinase B can be measured using any suitable substrate; for example, the peptide RPRAATF (SEQ ID No 1) is a preferred substrate but, for example, myelin basic protein and certain histones are also substrates of PKB. Preferably, the 3-phosphoinositide is phosphatidylinositol-3,4,5- trisphosphate or phosphatidylinositol-3,4-bisphosphate. We believe that PtdIns(3,4,5)P3 or a suitable phosphoinositide interacts with the PH domain of a PKB in order for PDKl to phosphorylate Thr- 308 of PKBα and activate this protein kinase. Our data suggests that a PKB molecule lacking the PH domain is activated and phosphorylated independently of PtdIns(3,4,5)P3. There are several mechanisms by which a drug (which interferes with the interaction between the kinase of the invention, for example, PDKl and PKB) may act. In one mechanism it may bind to PKB and prevent PKB from becoming activated by die kinase of the invention, for example PDKl . In the other mechanism, the drug may bind to me kinase of the invention (such as PDKl) and inhibit PDKl activity. In a further mechanism the drug may bind to PDKl and prevent it activating PKB. It is preferred if the screening assays of the invention are carried out using both a full-length PKB molecule (for example a GST-PKB fusion) or a molecule which, although not full length, retains a PH domain which is substantially capable of binding a suitable phospholipid such as PtdIns(3,4,5)P3, and a PKB in which the PH domain has been modified so mat the PKB is substantially incapable of binding a suitable phospholipid such as PtdIns(3,4,5)P3. Suitable modifications include deletion of all or part of the PH domain or mutations in the PH domain which substantially prevent binding of me suitable phospholipid. Compounds which prevent Ptdlns(3 ,4,5)P3 from interacting with PKB are particularly selected, which can be detected in the screen. Alternatively, it may be useful to use PKB lacking a functional PH domain in a screening assay of the invention, in this case no 3-phosphoinositide need be used in order for PDKl to activate PKB. A further aspect of the invention provides a compound identifiable by the screening methods disclosed herein. The methods effectively are screening assays for compounds which modulate the said 3-phosphoinositide-dependent protein kinase or its interactions with a 3-phosphoinositide or with a protein kinase B. Thus, the screening methods of the invention include methods for identifying compounds which compete with the 3-phosphoinositide (in particularphosphatidylinositol-3 ,4,5-trisphosphate orphosphatidylinositol- 3,4-bisphosphate) and which lead to inactivation or activation of the said 3-phosphoinositide-dependent protein kinase or other modulation of the enzyme activity; they also include screening methods for substances which bind to die said 3-phosphoinositide-dependent protein kinase and which reduce or enhance the activation of a protein kinase B or another suitable substrate (for example, ey may bind to said 3 -phosphoinositide- dependent protein kinase and prevent it interacting with a protein kinase B); and mey also include screening methods for substances which bind to a protein kinase B and which reduce or enhance its interaction with said 3-phosphoinositide-dependent protein kinase. The screening methods of the invention also include methods for identifying compounds which block the catalytic sites of PKB and d e protein kinase of the invention (for example, PDKl). Methods for carrying out this type of screening assay are well known in the art. It will be appreciated that in mose assays where a said 3-phosphoinositide- dependent protein kinase is required and the phosphorylation of a particular substrate requires the presence of a 3-phosphoinositide, a 3- phosphoinositide is present. Any suitable 3-phosphoinositide is useful but it is preferred if the 3-phosphoinositide is phosphatidylinositol-3,4,5- trisphosphate or phosphatidylinositol-3,4-bisphosphate. However, as is clear from the foregoing, some assay systems do not require the presence of a 3-phosphoinositide such as PtdIns(3,4,5)P3. The compounds identified in the methods may themselves be useful as drug or they may represent lead compounds for the design and syndiesis of more efficacious compounds which modulate the activity of the said 3- phosphoinositide-dependent protein kinase or its interactions with a 3- phosphoinositide or with a protein kinase B. Thus, a further aspect of the invention provides a method of modulating in a cell the activity of the said 3-phosphoinositide-dependent protein kinase or its interactions with a 3-phosphoinositide or with a protein kinase B, the method comprising introducing into me cell a compound identifiable in die screening assay described above. Preferably, the cell is in a human patient. Compounds, identifiable in the screening method, which mimic the effect of a 3-phosphoinositide, preferably phosphoinositol-3,4,5-trisphosphate or phosphoinositol-3,4-bisphosphate, are believed to be useful in treating diabetes. Compounds identifiable in the screening methods of the invention that inhibit PKB, PDKl or the activation of PKB by PDKl are believed to be useful in treating cancer. PKB is die cellular homologue of v-akt which is involved in leukaemias. Two isoforms of PKB are overexpressed in ovarian, pancratic and breast cancers. It is believed that PKB mediates protection of cells to apoptosis mediated, for example, by IGF-1. Overexpression of PKB may allow cancer cells to proliferate by stopping apoptosis. It will be appreciated mat certain compounds found in the screening methods may be able to enhance cell proliferation in a beneficial way and may be useful, for example in the regeneration of nerves or in wound healing. Further aspects of the invention provide me use of said 3- phosphoinositide-dependent protein kinase or variants, fragments, derivatives or fusions thereof or fusions of said variants, fragments or derivatives in a screening assay for compounds which modulate the activity of said protein kinase, in particular its interaction with 3- phosphomositide or a protein kinase B. The invention also includes the use of the said 3-phosphoinositide-dependent protein kinase, such as PDKl, to phosphorylate and active protein kinase B and it includes a method of activating PKB using a 3-phosphoinositide-dependent protein, such as PDKl . A still further aspect of the invention provides kits of parts that are useful in carrying out the screening methods. Conveniently, the kit of parts comprises a said 3-phosphoinositide-dependent protein kinase or a suitable variant or fragment or derivative or fusion thereof or a fusion of a variant or fragment or derivative (or a polynucleotide which encodes any of these) and a protein kinase B or a suitable variant or fragment or derivative or fusion diereof or a fusion of a variant or fragment or derivative (or a polynucleotide which encodes any of these). It will be appreciated that, depending on the screening method employed, it may additionally comprise a suitable 3 -phosphomositide or a suitable substrate for the protein kinase B. Abbreviations: PKB, Protein kinase B; PtdIns(3,4,5)P3, Phosphatidylinositol 3 ,4,5-tris phosphate; Ptdins(3 ,4,)P2, Phosphatidylinositol 3,4-bisphosphate; PI 3-kinase, Phosphomositide 3- kinase; PtdCho, Phosphatidylcholine; PtdSer, Phosphatidylserine; PH, pleckstrin homology. The invention will now be described in more detail widi reference to the following Examples and Figures wherein Figure 1. SDS Polyacrylamide gel of purified GST-PKBα. 293 cells were transiently transfected with the pEBG2T DNA construct expressing GST-PKBα, serum starved for 16 h and, after cell lysis, GST-PKBα was purified by affinity chromatography on glutathione-Sepharose (see Methods). "Sepharose" is a trade mark. The glutathione-Sepharose eluate (3 μg protein) was electrophoresed on a 10% SDS polyacrylamide gel and stained with Coomassie blue. "Coomassie" is a trade mark. The position of the molecular mass markers, glycogen phosphorylase (97 kDa), bovine serum albumin (67 kDa) and ovalbumin (43 kDa) are indicated. Figure 2. Identification and purification of a PtdIns(3,4,5)P3 dependent protein kinase (PDKl) which activates GST-PKBα. Following me PEG precipitation PDKl was chromatographed sequentially on SP-Sepharose (A) and heparin-Sepharose (B) and Peak 2 from the latter column was chromatographed on Mono S (C) (see Methods). "Mono S" is a trade mark. PDKl activity was assayed eidier in the presence of phospholipid vesicles comprising 100 μM PtdCho, 100 μM PtdSer, 10 μM D-enantiomer of sn-l-stearoyl 2-arachidonyl PtdIns(3,4,5)P3 (open circles) or vesicles comprising only 100 μM PtdCho and 100 μM PtdSer (closed circles). The broken lines indicate d e salt gradient and the solid line the absorbance at 280 nm. The amount of protein eluted from the Mono S column was too low see any absorbance at 280 nm. Figure 3. PDKl phosphorylates and activates GST-PKBα. (A) GST- PKBα (0.5 μM) was incubated with PDKl (12 U/ml), 10 mM Mg(Ac)2, 100 μM [γ 32 P]ATP, and vesicles comprising 100 μM PtdCho, 100 μM PtdSer, 10 μM D-enantiomer of -sn-l-stearoyl-2-arachidonyl PtdIns(3,4,5)P3 in Buffer B. At various times, aliquots were removed and eidier assayed for PKBα activity (closed circles) or for incorporation of phosphate into PKBα (open circles). Activities are presented relative to control experiments in which PDKl was omitted from the reaction mixture. Phosphorylation was assessed by counting die 32 P-radioactivity associated with the band of GST-PKBα after SDS-PAGE. (B) Same as (A) except that the effects of omitting PDKl , ATP, PtdSer/PtdCho, Ptdins(3,4,5)P3, heating PDKl at 55°C for 2 min, or adding 0.5% (by vol) Triton X-100 in die PDKl assay were studied. The assays were carried out for 60 min. Stippled bars show GST-PKBα activity and hatched bars GST-PKBα phosphorylation relative to a control assay in which PDKl, ATP, PtdCho/PtdSer and PtdIns(3,4,5)P3 were present. The results are presented as + . SEM for six deteπninations (two independent experiments). Figure 4. Dependence of PDKl activity on PtdIns(3,4,5)P3 concentration. GST-PKBα (0.5 μM) was incubated with PDKl (12 U/ml), 10 mM MgAc, 100 μM [γ 32 P]ATP and the indicated concentrations of D-enantiomer of l-stearoyl-2-arachidonyl Ptdins(3,4,5)P3 in either the presence of constant concentration of PtdCho and PtdSer (100 μM of each open circles) or in the presence of a 10 fold molar excess of the PtdSer/PtdCho (closed circles). After 30 min the extent of activation (A) and phosphorylation (B) of GST-PKBα was assessed as described in Materials and Methods. The results are presented as +. SEM for 2 experiments, each carried out in triplicate. Figure 5. PDKl phosphorylates PKBα at Thr-308. (A) GST-PKBα was phosphorylated by incubation for 60 min with PDKl (12 U/ml), and phospholipid vesicles comprising PtdCho, PtdSer, D-enantiomer of 1- stearoyl-2-arachidonyl Ptdins(3,4,5)P3, and Mg[γ32P]ATP (see legend to Fig 3), and men alkylated and digested wim trypsin (see Methods). The digest was applied to a Vydac 218TP54 C18 column (Separations Group, Hesperia, CA) equilibrated in 0.1 % (v/v) trifluoroacetic acid (TFA) in water. The column was developed with a linear acetonitrile gradient (diagonal line) at a flow rate of 0.8 ml/min and fractions of 0.4 ml were collected. 35% of the radioactivity applied to die column was recovered from the major 32 P-containing peptide at 26% acetonitrile (the remainder of the radioactivity eluted as numerous minor peaks). The elution positions of me tryptic peptides which contain Thr-308 and Ser-473 are marked [15] . (B) A portion of me major 32 P-containing peptide (500 cpm) from A was coupled covalently to a Sequelon arylamine membrane and analysed on an Applied Biosystems 470A sequencer using the modified programme described in [30] . 32 P radioactivity was measured after each cycle of Edman degradation. Figure 6. PDK-1 is activated specifically and stereospecifically by PtdIns(3,4,5)P3 and PtάTns(3,4)P2 lipids. GST-PKBα was incubated for 30 min at 30°C with Mg[γ 32 P]ATP in die presence (filled bars) and absence (open bars) of PDKl and phospholipid vesicles containing 100 μM PtdCho, 100 μM PtdSer, and various Ptdlns lipids (numbered 1-11 , see below) or Ins (1 ,3,4,5)P4, all at a final concentration of 10 μM in the assay. Reactions were terminated by the addition of 1 % (by vol) Triton X-100 to the assay and in (A) the activity of GST-PKBα was determined as described under Methods. (B) The phosphorylation of GST-PKBα was assessed by autoradiography of the Commassie blue-stained band corresponding to GST-PKBα (Fig 1). The results are presented as fold- activation of GST-PKBα ± SEM for 6-8 determinations (three independent experiments). Lipids 1 and 2 are the D and L-enantiomers of --M-l-stearoyl-2-arachidonyl Ptdins(3,4,5)P3 respectively, and lipids 3 and 4 are the D and L-enantiomers of -sn-2-arachidonyl-3-stearoyl Ptdins(3,4,5)P3 respectively. Lipid 5 is racemic -!>«-l,2-dilinoleoyl Ptdins(3,4,5)P3. The remaining lipids are all D-enantiomers. Lipid 6 is -m-1,2 di-palmitoyl Ptdins(3,4,5)P3, lipid 7 is sn- 1,2 di-palmitoyl Ptdins(3,4)P2, lipid 8 is s/ι-1,2 di-palmitoyl Ptdins(3,5)P2. Lipid 9 is Ptdins(4,5)P2, and lipid 10 is Ptdlns 4P which are both purified lipid derived from Folch fraction type-I brain extract. Lipid 11 is -sτz-1 ,2 di- palmitoyl Ptdlns-3P. IP4 is Ins(l,3,4,5)P4. Figure 7. Proposed mechanism by which insulin induces the activation of PKBα. The activation of the insulin receptor by insulin causes me receptor to phosphorylate itself at several tyrosine residues. This leads to the docking of insulin receptor substrate- 1 (IRS-1) and IRS-2 and their phosphorylation at multiple tyrosine residues by the insulin receptor. Several phosphorylated tyrosine residues on IRS1 and IRS2 men interact with SH2 domains on the p85 subunit of PI 3-kinase, leading to me recruitment of the pi 10 catalytic subunit of PI 3-kinase to cell membranes and its activation [31]. PI 3-kinase then phosphorylates Ptdins(4,5)P2 at me D-3 position of the inositol ring, resulting in the formation of the second messenger Ptdins(3,4,5)P3 whose levels (in a typical cell) rise from 0.1 % to 1-2% of the PtdIns(4,5)P2 content in the plasma membrane [31] . PtdIns(3,4,5)P3 interacts with, and activates PDKl which partially activates PKBα by phosphorylating it at Thr-308. Maximal activation of PKBα also requires the phosphorylation of Ser-473 by an unknown kinase . The insulin-induced phosphorylation of Ser-473, like the phosphorylation of Thr-308, is prevented by inhibitors of Ptdlns 3-kinase [15], suggesting mat Ser-473 may be phosphorylated by a distinct 3-phosphoinositide- dependent protein kinase (PDK2). However, the Ser-473 kinase may be activated indirectly by 3-phosphoinositides by mechamsms discussed in the text. For this reason, the pathway from PtdIns(3,4,5)P3 to the phosphorylation of Ser-473 is shown by broken lines wim a question mark after PDK2. In skeletal muscle, the activation of PKBα may increase the rate of glucose uptake [9] and glycogen synthesis [7] and stimulate protein translation [8] . In neurons and other cells PKBα activation may provide a survival signal by suppressing apoptosis [10,11]. Figure 8. Details of IMAGE Consortium clone ID 526583. Figure 9. Details of IMAGE Consortium clone ID 626511. Figure 10. Nucleotide sequence coding for, and deduced amino acid sequence of, PDKl (SEQ ID No 2, SEQ ID No 3). Figure 11. Alignment of the amino acid sequences of human PDKl and Drosophila DSTPK61. The alignment was carried out using the Clustal W program [46]. Asterisks indicate identities between PDKl and STK61. The catalytic domain comprises residues 83-342 of PDKl and residues 165-487 of STPK61. The putative PH domains lie between residues 450 and 550 of PDKl and 581 and 684 of STPK61B. Figure 12. GST-PDK1 and GST-DSTPK61 activate and phosphorylate PKBα in a Ptdlns (3, 4, 5) P 3 or PtdIns(3,4)P 2 dependent manner. GST- PKBα was incubated for 30 min at 30°C with either 5 U/ml GST-PDK1 (panels A, B) or GST-DSTPK61 (panels C, D) with Mg[γ 32 P]ATP and phospholipid vesicles containing 100 μM PtdCho, 100 μM PtdSer, and various Ptdlns lipids (numbered 1-5, see below) all at a final concentration of 10 μM in me assay. Under these conditions, the increase in PKBα activity and phosphorylation was linear with respect to time (see Metiiods). In panels A and C, die assays were terminated by making the incubations 1 % (by vol) in Triton X-100 (see Ref 21), and the increase in specific activity of GST-PKBα was determined. In panels B and D, the reactions were terminated by making the solutions 1 % in SDS, the samples were subjected to SDS/polyacrylamide gel electrophoresis, and die phosphorylation was assessed by autoradiography of the Coomassie blue-stained band corresponding to GST-PKBα. The results are presented in panels A and C as the increase in the specific activity of GST-PKBα (U/mg), relative to a control incubation in which GST-PDK1 or GST- DSTPK61 was omitted (+ SEM for 6-9 determinations, tiiree independent experiments). Under all conditions the increase in bom activity and phosphorylation of GST-PKBa was linear with time. Track 1, buffer control; Track 2, sn-l-stearoyl-2-arachidonyl-D-Ptdins(3,4,5)P 3 ; Track 3, 5/2-1 ,2 di-palmitoyl-D-Ptdins(3,4)P 2 ; Track 4 is PtdIns(4,5)P 2 (purified from Folch brain fraction); Track 5, sn-l ,2 di-palmitoyl-D-PtdIns-3P. Figure 13. PDKl phosphorylates PKBα at Thr308. GST-PKBα was maximally phosphorylated by incubation for 30 min with 25 U/ml of either GST-PDK1 (A) or GST-DSTPK61 (B) and phospholipid vesicles comprising PtdCho, PtdSer, the D-enantiomer of l-stearoyl-2-arachidonyl PtdIns(3,4,5)P 3 , and Mg[γ 32 P]ATP (10 6 cpm per nmol). After 30 min, the samples were alkylated with 4-vinylpyridine, digested with trypsin [21] and applied to a Vydac 218TP54 C 18 column (Separations Group, Hesperia, CA) equilibrated in 0.1 % (v/v) trifluoroacetic acid (TFA). The column was developed with a linear acetonitrile gradient (diagonal line) at a flow rate of 0.8 ml/min and fractions of 0.4 ml were collected. 38% (panel A) and 45 % (panel B) of the radioactivity applied to die column was recovered in the major 32 P-contøining peptide eluting at 26% acetonitrile, while contains Thr308. The elution position of the typtic peptide containing Ser473 is also marked [see ref 20 and Fig 15] . Figure 14. PKBα is activated by cotransfection with PDKl in 293 cells. (A) 293 cells were transiently transfected with DNA constructs expressing either HA-PKBα or bom HA-PKBα and Myc-PDKl . The cells were men stimulated for 10 min with or without 50 ng/ml IGF1, the HA- PKBα immunoprecipitated from the lysates and assayed. The results are expressed relative to the specific activity of wild type HA-PKBα in unstimulated 293 cells (0.03 ± 0.5 U/mg). No PKBα activity was detected in mock transfections in which the cells were transfected witii PCMV5 vector alone (data not shown). (B) 6 μg of protein from each lysate was elecfrophoresed on a 10% SDS/polyacrylamide gel and immunoblotted using either a monoclonal HA-antibody to detect HA- PKBα or a monoclonal Myc-antibody to detect Myc-PDKl . The molecular mass markers are glycogen phosphorylase (97 kDa), bovine serum albumin (67 kDa) and ovalbumin (43 kDa). Figure 15. Overexpression of PDKl in cells induces phosphorylation of PKBα at Thr308. 293 cells transiently transfected with either wild type HA-PKBα (panels A and C) or HA-PKBα and Myc-PDKl (panels B and D) were incubated witii 32 P-orthophosphate, then treated for 10 min without (panels A and B) or witii (panels C and D) 50 ng/ml IGF 1. The 32 P-labelled HA-PKBα was immunoprecipitated from the lysates, treated with 4-vinylpyridine, and electrophoresed on 1 10% polyacrylamide gel. The HA-PKBα was excised from the gel, digested with trypsin and chromatographed on a C 18 column (see legend to Fig 13) to resolve the four major phosphopeptides which are phosphorylated at Ser- 124, Ser473 , Thr308 and Thr450 respectively [20]. The identity of each phosphopeptide was established by phospho-amino acid analysis and solid phase sequencing. Similar results were obtained in two separate experiments for (panels A and C), and in tiiree separate experiments (panels B and D). Figure 16. Role of the PH domains of PKBα and PDKl. (A) 0.5 μg of either GST-PKBα or GST-ΔPH-PKBα were incubated for 30 min at 30°C with either 2.3 nM GST-PDK1 (residues 1-556) with Mg[γ 32 P]ATP and phospholipid vesicles containing 100 μM PtdCho, 100 μM PtdSer either in the presence or absence of 10 μM PtdIns(3,4,5)P3 in a 20 μl assay. The assays were terminated by making the incubations 1 % (by vol) in Triton X-100 as in Example 1, and die increase in specific activity of GST-PKBα was determined. The basal activity of GST-PKBα was 2.5 U/mg and that of GST-ΔPH-PKBα was 8 U/mg. At the high concentration of GST-PDK1 used in this assay the rate of activation of full length wild type GST-PKBα is not linear with time whereas the activation of GST-ΔPH-PKBα is linear. When the experiments are carried out at 20-fold lower concentrations of GST-PDK1 a similar extent of activation of wild-type GST-PKBα is achieved as tiiat shown in the figure for GST- ΔPH-PKBα by 2.3 nM GST-PDK1. (B) as in (A) except that 0.5 μg of GST-PKBα was incubated with 2.5 nM GST-ΔPH-PDK1 (residues 1 to 450) in the presence of phospholipid vesicles containing 100 μM PtdCho, 100 μM PtdSer and 10 μM of either, s/2-l-stearoyl-2-arachidonyl-D- PtdIns(3,4,5)P3 (Track 1); 5/t-l-stearoyl-2-arachidonyl-L-PtdIns(3,4,5)P3 (Track 2), sn-l ,2 di-palmitoyl-D-PtdIns(3,4,5)P3 (Track 3), sn-l,2 di- palmitoyl-D-PtdIns(3,4,5)P3 (Track 4), PtdIns(4,5)P2 (purified from Folch brain fraction Track 5) and sn-\ ,2 di-palmitoyl-D-PtdIns-3P (Track 6). The results are presented as the increase in the specific activity of GST- PKBα (U/mg), (± SEM for 6-9 determinations, three independent experiments), relative to a control incubation in which GST-PDK1 is omitted. Figure 17. Evidence that PDKl and DSTPK61 possess a Pleckstrin- Homology domain. Sequence alignment of PH domains that have a known tertiary structure with the putative PH domains of PDKl and DSTPK61. Alignment was done using the program AMPS (Barton & Sternberg (1990) J. Mol. Biol. 212, 389-402) and formatted using AMAS (Livingstone & Barton (1993) Comp. Appl. Bio. Sci. 9, 745-756) with some manual adjustment to ensure coincidence of secondary structure regions. Regions containing conserved residues are coloured green and the invariant tryptophan (Trp-535) is coloured red. General regions of secondary structure are denoted by the blue (beta strand) and green (alpha helix) bands. The Pleckstrin-Homology sequences are those found in human Pleckstrin, PLS; human spectrin, SPC; human dynamin DYN, and rat phospholipase C-δ, PLCδ. Numbering is based on the PDKl sequence (Fig 10). Figure 18. SDS Polyacrylamide gel of purified GST-PDK1 and GST- DSTPK61. GST-PDK1 encoding residues 52-556, Lane 1. 3 μg protein) and GST-DSTPK61 (Lane 2.6 μg protein) were elecfrophoresed on 1 7.5% SDS polyacrylamide gel and stained with Coomassie blue. The position of the molecular mass markers, glycogen phosphorylase (97 kDa), bovine serum albumin (67 kDa) and ovalbumin (43 kDa) are indicated. The other GST-PDK1 constructs used in this study were all expressed at a similar level of purity as the GST-PDK1 preparation shown in Lane 1 (data not shown). Example 1 : Purification and characterisation of a 3- phosphoionositide-dependent protein kinase (PDKl) that phosphorylates and activates protein kinase Bα Summary Background: Protein kinase B (PKB), also known as c-Akt, is activated rapidly when cells are stimulated with insulin and growth factors, and much of me current interest in this enzyme stems from the observation that it lies downstream of phosphomositide 3-kinase. We recently showed that insulin or IGF1 induce the phosphorylation of PKB at Thr-308 and Ser-473. The phosphorylation of both residues is required to activate PKB maximally, and the insulin or IGF 1 -induced phosphorylation of both residues is prevented by incubating cells witii inhibitors of PI-3 kinase. Results: A protein kinase has been purified 500,000-fold from rabbit skeletal muscle extracts which phosphorylates protein kinase Bα (PKBα) at Thr-308 and increases its activity > 30-fold. The kinase was only active in die presence of low micromolar concentrations of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] or phosphatidylinositol 3,4-bisphosphate [PtdIns(3,4)P2] and has tiierefore been termed Ptdlns(3, 4, 5)P3 -dependent protein kinase-1 (PDKl). The D- enantiomers of ,s?z-l-stearoyl-2-arachidonyl PtdIns(3,4,5)P3 and sn-2- arachidonyl-3-stearoyl Ptdins(3,4, 5)P3 potently activated PDKl , but die L-enantiomers of these derivatives were almost ineffective, -sn-1,2- dipalmitoyl PtdIns(3,4,5)P3 and -m-l,2-dipalmitoyl PtdIns(3,4,)P2 bom activated PDKl to a similar extent, but were ~ 3-fold less effective than the-syt-l-stearoyl-2-arachidonylandsft-2-arachidonyl-3-stearoylderivatives. PtdIns(3,5)P2, PtdIns(4,5)P2, PtdIns(4)P, PtdIns(3)P and inositol 1,3,4,5- tetrakisphosphate did not activate PDKl at all. None of the inositol phospholipids tested activated or inhibited PKBα or induced its phosphorylation under the same conditions. PDKl activity was unaffected by wortmannin, indicating tiiat it is not likely to be a PI 3-kinase family member. Conclusions: PDKl is likely to be one of the protein kinases which mediate the activation of PKB by insulin and growth factors. PDKl may therefore play a key role in mediating many of the actions of the second messengers, PtdIns(3,4,5)P3 and/or PtdIns(3,4)P2. Materials and Methods Materials. PtdSer (pig brain) was purchased from Doosan Serdary Research Laboratories (New Jersey, USA) ands/2-l-stearoyl-2-arachidonyl PtdCho from Sigma (Poole, UK). Ptdlns 4P and PtdIns(4,5)P2 were purified as described previously from Folch fraction type-1 extract of bovine brain (Sigma) [26]. Synthetic s/z-l,2-dipalmitoyl analogues of PtdIns(3,4,5)P3, PtdIns(3,4)P2, PtdIns(3,5)P2 and Ptdlns 3P were made as described previously [18] . Synthetic D and L enantiomers of sn-l- stearoyl-2-arachidonyl Ptdlns(3 ,4,5)P3 , j , n-2-arachidonyl-3-stearoyl PtdIns(3,4,5)P3 and die D enantiomer of -sτϊ-l-linoleoyl-2-linoleoyl PtdIns(3,4,5)P3 were synthesised from inositol (Gaffney and Reece 1997, manuscript submitted for publication). All phospholipids were 97-98% pure. Synthetic phosphatidylinositol bisphosphates were stored at -20 °C as solutions in dimethyl sulphoxide (DMSO) and phosphatidylinositol trisphosphates in either DMSO or water. All other phospholipids were stored in chloroform-methanol solvents. The peptide used to assay PKBα, (RPRAATF) (SEQ ID No 1) [16] and TTYADFIASGRTGRRNAIHD ((SEQ ID No 10) the specific peptide inhibitor of cyclic AMP dependent protein kinase, termed PKI) were synthesised by Mr F. Barry Caudwell (MRC Protein Phosphorylation Unit, Dundee) on an Applied Biosystems 431 A peptide synthesiser, and their concentrations were determined by quantitative amino acid analysis. Glutathione Sepharose was purchased from Pharmacia (Milton Keynes, UK) and alkylated trypsin from Promega (Southampton, UK). Buffer solutions: Buffer A; 50 mM Tris/HCl pH 7.5, 1 mM EDTA 1 mM EGTA, 1 % (by vol) Triton X-100, 1 mM sodium orthovanadate, 10 mM sodium β- glycerophosphate, 50 mM NaF, 5 mM sodium pyrophosphate, 1 μM Microcystin-LR, 0.27 M sucrose, 1 mM benzamidine, 0.2 mM phenylmediylsulphonyl fluoride (PMSF), 10 μg/ml leupeptin, 0.1 % (by vol) 2-mercaptoethanol. Buffer B; 50 mM Tris/HCl pH 7.5, 0.1 mM EGTA, 0.03 % (by vol) Brij- 35, 0.27 M sucrose, 0.1 % (by vol) 2-mercaptoethanol. Buffer C; 50 mM Tris/HCl pH 7.5, 2 mM EDTA, 2 mM EGTA, 50 mM NaF 0.1 % (by vol) 2-mercaptoethanol, 0.1 mM PMSF, 1 mM benzamidine. Expression of GST-PKBα in 293 cells. The DNA sequence encoding PKBα was subcloned into the eukaryotic expression vector PEBG2T that has been used to overexpress GST-fusion proteins in eukaryotic cells under an EFlα promoter [27]. A PCR reaction was set up to generate a full length cDNA encoding the PKBα gene with a BamHlsite at the 5 'end of the cDNA that is in frame with the GST sequence of the PEBG2T vector and the ATG initiation codon of PKBα, and a Kpnl site at the 3' end, using the human PCMN5 -HA-PKBα plasmid [15]. The DΝA sequence of the BamHI /Kpnl cDΝA fragment was checked and then subcloned into the unique BamHI /Kpnl restriction sites on the pEBG 2T expression vector. In order to prepare GST-PKBα, 40, 10 cm diameter dishes of human embryonic kidney 293 cells were culmred and each dish transfected with 20 μg of GST PKBα expression construct using the modified calcium phosphate method described previously for overexpression of haemaglutinin tagged PKBα in 293 cells [15]. 24 h after transfection, the cells were serum starved for 16 h and each dish of cells lysed in 1 ml of ice-cold Buffer A. The 40 lysates were pooled, centrifuged at 4°C for 10 min at 13, 000 x g and die supernatant incubated for 60 min on a rotating platform with 800 μl of glutathione- Sepharose previously equilibrated in Buffer A. The suspension was centrifuged for 1 min at 3000 x g, the beads washed three times with 10 ml of Buffer A containing 0.5 M ΝaCl, and tiien a further 10 times with 10 ml of Buffer B to ensure complete removal of all the Triton X-100 which interferes with the activation of GST-PKBα by PDKl (Fig 3B). GST-PKBα was eluted from the resin at ambient temperature with three 1 ml portions of Buffer B containing 20 mM glutatiiione pH 8.0. The combined eluates (0.65 mg/ml protein) were divided into aliquots, snap frozen in liquid nitrogen, and stored at -80°C. Preparation of phospholipid vesicles Phospholipid vesicles comprising 1 mM PtdCho, 1 mM PtdSer and 0.1 mM Ptdlns lipids were prepared, dried to a film under vacuum and resuspended with vortexing into 10 mM Hepes, pH 7.3. The cloudy solution of multilamellar and large unilamellar vesicles was bath-sonicated for 20 min, after which a clearer suspension of smaller unilamellar vesicles was obtained. Solutions were stored at 4°C at concentrations 10- fold higher than tiiose required in the assay and used witiiin 2-4 days. Purification of PDKl from rabbit Skeletal muscle Day 1. A female New Zealand White rabbit was killed with a lethal dose of sodium pentobarbitone. Skeletal muscle from the hind limbs and back (500g) was excised rapidly and placed on ice. All subsequent steps were carried out at 0-4°C. The muscle was minced, homogenized in 2.5 vol of 25 mM Tris/HCl pH 7.5, 4 mM EDTA, 2 mM EGTA, 50 mM NaF, 0.1 % (by vol) 2-mercaptoethanol, 0.1 mM PMSF and 1 mM benzamidine and centrifuged for 30 min at 4200 x g. The supernatant was filtered through glass wool and poured dirough a Buchner funnel containing 10 g of Q AE-Sephadex equilibrated in Buffer C . The column was washed with one litre of Buffer C containing 50 mM NaCl, and washed with 700 ml of Buffer C containing 0.2 M NaCl to elute PDKl. A 50% (by mass) solution of polyethylene glycol (PEG) was added to die eluate to bring the final concentration of PEG to 4% . After stirring on ice for 60 min, the suspension was centrifuged for 15 min at 10 000 x g. The supernatant was decanted and made 15% in PEG by further addition of 50% (by mass) PEG. After stirring for a further 60 min on ice, die suspension was again centrifuged for 15 min at 10 000 x g. The supernatant was discarded and the precipitate dissolved in 50 ml of ice cold Buffer B, filtered through a 0.25 μm filter and then chromatographed on an SP-Sepharose column (11 x 1.6 cm) equilibrated in Buffer B. The column was developed witii a 300 ml linear gradient of NaCl to 0.5 M at a flow rate of 3 ml/min and 6 ml fractions were collected (Fig 2A). The active fractions were pooled and applied directly on to a 5 ml heparin-Sepharose column (HiTrap) equilibrated in Buffer B containing 0.1 M NaCl. The column was developed with a 90 ml linear salt gradient to 0.9 M NaCl at a flow rate of 2 ml/min and fractions of 1 ml were collected. PDKl activity eluted as 2 peaks. Peak-1 , comprising - 30% of the activity, was eluted at 0.5 M NaCl, while Peak 2 comprising - 70% of the activity, eluted at 0.7 M NaCl (Fig 2B). Day 2. The active fractions of Peak 2 were pooled concentrated to 0.2 ml by ultrafiltration, diluted to 2.0 ml in Buffer B, and loaded on to a Mono S column (5 cm x 1.6 mm) equilibrated in Buffer B. The column was developed witii a 4.0 ml linear gradient of salt to 0.15 M MgC12 at a flow rate of 0.2 ml/min and 0.1 ml fractions were collected. Fractions containing PDKl were aliquoted, snap frozen in liquid nitrogen, and stored at -80°C. No significant loss of activity occured upon thawing. Assay of PDKl. The assay was carried out in two stages; in the first, GST-PKBα was incubated with PDKl in the presence of MgATP and phospholipid vesicles to permit activation of GST-PKBα. In the second stage, the solution was made 0.5 % (by vol) in Triton XI 00 (which completely inhibits phosphorylation and activation of GST-PKBα without affecting GST-PKBα activity, see Fig 3B), together with Mg[γ32P]ATP, and the specific PKBα substrate peptide RPRTAAF (SEQ ID No 1) [16]. In Stage 1 , an 18 μl reaction mixture was set up containing 50 mM Tris/HCl pH 7.5, 0.1 mM EGTA, 0.1 % (by vol) 2-mercaptoethanol, 0.1 mM EGTA, 2.5 μM PKI, 1 μM microcystin-LR, 10 mM Mg(Ac)2, 100 μM unlabelled ATP, 0.6 μM GST-PKBα, 100 μM PtdSer, 100 μM PtdCho in the presence or absence of 10 μM PtdIns(3,4,5)P3. The assay was initiated by the addition of 2 μl of PDKl and, after incubation for 30 min at 30 °C, stage 2 of the assay was initiated by die addition of 30 μl of a mixmre containing 50 mM Tris/HCl pH 7.5, 0.1 mM EGTA, 0.1 % (by vol) 2-mercaptoethanol, 0.1 mM EGTA, 2.5 μM PKI, 1 μM microcystin- LR, 10 mM Mg(Ac)2, 100 μM [γ 32 P]ATP (200-400 cpm/pmol), 100 μM of the peptide RPRTAAF and 1.25 % (by vol) Triton X-100. After 10 min at 30°C, the reactions were terminated by spotting die reaction mixmre on to p81 phosphocellulose paper. The papers were washed in phosphoric acid and analysed as described previously [28]. A control reaction in which GST-PKBα was omitted was taken as die blank and was always less than 5% of d e activity measured in die presence of GST- PKBα. The basal GST-PKBα activity is the activity measured in the absence of PDKl . One Unit of PDKl activity was defined as that amount required to increase the basal activity of GST-PKBα by 1 Unit of activity. 1 Unit of GST-PKBα activity was that amount of enzyme required to catalyse the phosphorylation of 1 nmol of the peptide RPRTAAF (SEQ ID No 1) in 1 min. The assays were linear with time up to a final concentration of 2 U/ml of PDKl activity in tiie assay. Phosphorylation of GST-PKBα by PDKl. The incubations were identical to the Stage 1 described above except that [γ 3 P] ATP (200-400 cpm/pmol) was used instead of unlabelled ATP. The reactions were terminated by making the solution 1 % (by mass) in SDS. The samples were run on a 7.5 % SDS-polyacrylamide gel and, after staining wim Coomassie blue, the gels were autoradiographed. The Coomassie blue- staining bands corresponding to GST-PKBα were excised and die 32 P- radioactivity associated witii each band was quantified. Mapping the site on GST-PKBα phosphorylated by PDKl . GST-PKBα was phosphorylated in the presence of the D-enantiomer of -syi-l-stearoyl- 2-arachidonyl PtdIns(3,4,5)P3 except that the scale of the reaction was increased 10-fold and the specific activity of the [γ 32 P] ATP was increased to 1500 cpm pmol. The reaction was stopped by the addition of SDS and 2-mercaptoethanol to final concentrations of 1 % (by mass) and 1 % (by vol) respectively, and heated for 5 min at 95 °C. After cooling to ambient temperamre, 4-vinylpyridine was added to a concentration of 2.5 % (by vol) and the sample left on a shaking platform for 1 h at 30° C to alkylate cysteine residues. The sample was then electrophoresed on a 7.5 % SDS polyacrylamide gel, and the 32 P-labelled GST-PKBα eluted from the gel and digested with trypsin as described previously [15] . Results Purification of GST-PKBα from 293 cells. PKBα was expressed in 293 cells as a fusion protein with glutatiiione S-transferase (GST) at the N- terminus, and purified on glutatiiione Sepharose. The preparation showed a major Coomassie blue-staining protein band of apparent molecular mass 85 kDa corresponding to GST-PKBα (Fig 1). The purity estimated by densitometric analysis of the gels was > 70% and 2 mg of purified GST- PKBα was obtained routinely in each preparation made from 40, 10 cm dishes of 293 cells. GST-PKBα from unstimulated 293 cells possessed very low activity, but was activated 20-fold and 45-fold after stimulation of 293 cells with insulin and IGF1 , respectively (data not shown), indicating tiiat it is recognised by the upstream protein kinase(s) that activates PKBα in vivo. GST-PKBα from unstimulated 293 cells was therefore used as the substrate with which to identify its upstream activators. Identification of a PtdIns(3,4,5)P3 dependent protein kinase that activates PKBα. We identified an activator of GST-PKBα in skeletal muscle cytosol mat eluted from Q AE-Sephadex at 0.25 M salt and purified it a further 30, 000-fold from the QAE-Sephadex eluate (Table 1). The activator was completely dependent on PtdIns(3,4,5)P3 for activity and, because it phosphorylates PKBα (see below), it is hereafter termed PtdIns(3,4,5)P3-dependent protein kinase- 1 (PDKl). PDKl could not be detected in the crude cytosol, but assuming a recovery of 50% through the initial batchwise chromatography on QAE-Sephadex, the overall purification was about 500, 000-fold, and the entire preparation could be completed within 36 h. PDKl was eluted as a single peak from S-Sepharose (Fig 2A), but resolved into two species on heparin-Sepharose. The minor component (Peak 1) eluted at 0.5M NaCl and the major component (Peak 2) at 0.7M NaCl (Fig 2B). All further experiments were carried out with the Peak 2 enzyme from heparin-Sepharose further purified through Mono S (Fig 2C), unless stated otherwise. After the final step the peak 2 enzyme, which was devoid of PKB activity, showed tiiree major protein staining bands witii apparent molecular masses of 85 , 67 and 45 kDa. Only the 67 kDa band became phosphorylated upon incubation wit MgATP and phosphorylation was greatly increased in die presence of PtdIns(3,4,5)P3. The sequences of two tryptic peptides from the 67 kDa band were highly homologous to regions of the catalytic domains of otiier protein kinases (data not shown). The data indicate tiiat PDKl is a novel 67 kDa protein kinase, distinct from other protein kinases reported to be activated by PtdIns(3,4,5)P3, such as PKCe and PKCf. Table 1. Purification of PDKl from rabbit skeletal muscle. 500 g of muscle was used in this preparation. The protein was estimated by the procedure of Bradford [29]. PEG, polyethyleneglycol . /> O n /) 10 π o > Phosphorylation and activation of GST-PKBα by PDKl. Purified PDKl phosphorylated GST-PKBα in the presence of MgATP and phospholipid vesicles containing PtdCho, PtdSer and PtdIns(3,4,5)P3 to a level approaching 0.7 moles of 32P/mol protein (Fig 3A). Phosphorylation was paralleled by a > 30-fold increase in activity (Fig 3 A) which reached a specific activity of 80 U/mg. This is similar to the activity of PKBα which has been partially activated by mutating Thr-308 to Asp [15,16], Omitting either PtdIns(3,4,5)P3 or PDKl or ATP from the reaction abolished activation and phosphorylation of GST-PKBα (Fig 3B). Moreover, addition of 0.5% (by vol) Triton-XlOO to the assays also prevented the activation and phosphorylation of GST-PKBα by PDKl (Fig 3B), as did incubating PDKl for 2 min at 55 °C. In the absence of PtdCho/PtdSer vesicles, Ptd Ins(3,4,5)P3 was at least 15-fold less effective in activating PDKl (Fig 3B). When PDKl was incubated for 30 min at 30°C in the presence of phospholipid vesicles containing PtdCho, PtdSer, PtdIns(3,4,5)P3 and MgATP, and then for 2 min at 55 °C to inactivate PDKl, the phospholipid vesicles were unable to activate or phosphorylate GST-PKBα, unless more PDKl was added (data not shown). These observations establish that PDKl does not activate GST-PKBα indirectly by converting PtdIns(3,4,5)P3 to another product that stimulates the autophosphorylation and autoactivation of GST-PKBα. Dependence of PDKl on PtάTns(3,4,5)P3 concentration. We next investigated the effect of varying the PtdIns(3,4,5)P3 concentration on the ability of PDKl to activate (Fig 4A) and phosphorylate (Fig 4B) GST- PKBα. These experiments were carried out eidier by varying the concentration of PtdIns(3,4,5)P3 whilst maintaining the concentration of both PtdCho and PtdSer at 100 μM or by maintaining a 10-fold excess of PtdCho and PtdSer over PtdIns(3,4,5)P3. Under both conditions, die concentration of PtdIns(3,4,5)P3 required for half maximal activation or phosphorylation was 1-2 μM, with an optimal effect at 10 μM. PDKl phosphorylates Thr-308 of PKBα. In order to identify the residue(s) in PKBα phosphorylated by PDKl, 32P-labelled GST-PKBα tiiat had been phosphorylated to 0.4-0.6 mol/mol witii PDKl , was digested witii trypsin and chromatographed on a C18 column [15]. One major 32 P- labelled peptide was observed that eluted at 26% acetonitrile (Fig 5A). This peptide, which coeluted witii the 32 P-labelled tryptic peptide containing Thr-308 [15] , was found to contain phosphothreonine only (data not shown). When this peptide was subjected to solid phase sequencing, 32 P-radioactivity was released after the first cycle of Edman degradation (Fig 5B) corresponding to Thr-308 [15] . Importantly, no 32 P-labelled peptide eluted at the position corresponding to die tryptic peptide containing Ser-473, which elutes at 24% acetonitrile (Fig 5 A, ref 15). These data establish that PDKl only phosphorylates PKBα at Thr-308 in vitro. Lipid specificity of PDKl. We next smdied the ability of a panel of Ptdlns derivatives to activate PDKl when present in a vesicle background containing PtdCho/PtdSer. The predominant form of PtdIns(3,4,5)P3 which occurs naturally is likely to be predominantly -sw-l-stearoyl, 2- arachidonyl D-phosphatidylinositol 3,4,5-trisphosphate [17] (based on the structure and fatty acid composition of natural Ptdlns). Synthetic sn-l- stearoyl, 2-arachidonyl D-PtdIns(3,4,5,)P3 (lipid 1 in Fig 6) proved highly effective, activating PDKl activity 13-fold. By contrast, the L-enantiomer of this lipid induced only a 1.7-fold increase in PDKl activity, which may be accounted for by trace contamination witii the D-enantiomer. Whilst the enantiomeric configuration of the head group was of critical importance for activating PDKl, that of the glycerol moiety was not. Thus -sτϊ-2-arachidonyl, 3-stearoyl D- and L-PtdIns(3,4,5)P3 gave signals which were indistinguishable from the sn-l,2-derivatives (16-fold and 2.3- fold, respectively). The importance of unsaturated fatty acids in the diacylglycerol moiety is strongly indicated by me fact that -m-1 ,2- dilinoleoyl D-PtdIns(3,4,5)P3 (linoleic acid is C18:2) was the most effective lipid tested causing a 36-fold increase in GST-PKBα activity, whilst -yn-l ,2-dipalmitoyl D-PtdIns(3,4,5)P3 induced only a 5.5-fold activation (palmitic acid is C16:0). In each of these experiments, the phosphorylation of GST-PKBα (Fig 6B) correlated with the extent of activation (Fig 6A). Interestingly, sn -1 ,2-dipalmitoyl PtdIns(3,4)P2 (lipid 7, Fig 6) and sn - 1 ,2-dipalmitoyl PtdIns(3,4,5)P3 (lipid 6, Fig 6) activated PDKl to the same extent, both inositol phospholipids increasing GST-PKBα activity about 6-fold. However, PtdIns(3,5)P2 (lipid 8 Fig 6), PtdIns(4,5)P2 (lipid 9 Fig 6), Ptdlns 4P (lipid 10, Fig 6), Ptdlns 3P (lipid 11, Fig 6) and Ins(l ,3,4,5)P4 did not activate PDKl or induce the phosphorylation of GST-PKBα. In the absence of PDKl none of the Ptdlns derivatives tested induced any activation or phosphorylation of GST-PKBα (Fig 6). Discussion The identification and purification of PDKl was greatly facilitated by the development of a specific peptide substrate (RPRAATF) (SEQ ID No 1) for PKBα [16] . Other substrates used to assay PKB, such as histone H2B, myelin basic protein and Crosstide are phosphorylated by many protein kinases in cell extracts and obscured the detection of PDKl . The use of soluble GST-PKBα as a substrate was also important because immunoprecipitated HA-PKB was not phosphorylated effectively by PDKl. PDKl was found to phosphorylate PKBα at Thr 308 and to enhance its activity > 30-fold. Since the phosphorylation of Thr-308 induced by insulin or IGF1 in vivo is prevented by inhibitors of Ptdlns 3- kinase and PDKl has an absolute requirement for PtdIns(3,4,5)P3 or PtdIns(3,4)P2, PDKl is likely to be the enzyme which phosphorylates PKBα at Thr-308 in vivo. PDKl activity is unaffected by worrmannin up to 2 μM (data not shown), indicating that it is not a Ptdlns 3-kinase family member. The full activation of PKBα in vitro requires the phosphorylation of Ser- 473 as well as Thr-308 [15] . Thus mutation of either Thr-308 or Ser-473 to Asp stimulates PKBα about 5 -fold but, if both residues are mutated to Asp, activity is increased 18-fold. Similarly, phosphorylation of Ser-473 stimulates PKBα activity 7-fold, but if the phosphorylation of Ser-473 is combined witii the mutation of Thr-308 to Asp, activity is increased 25- fold [15] . PKBα that has been partially activated by phosphorylation of Thr-308 or by the mutation of this residue to Asp does not become phosphorylated at Ser-473 in vitro upon incubation witii MgATP in the presence of PtdIns(3,4,5)P3 ([15], Fig 5) indicating that Ser-473 is unlikely to be an autophosphorylation event, catalysed by PKBα itself. Ser-473 can be phosphorylated in vitro by MAP kinase-activated protein kinase-2, but this enzyme cannot mediate the insulin or IGF 1 -induced phosphorylation of PKBα at Ser-473 for reasons discussed in [15] . Since the insulin/IGF 1 -induced phosphorylation of Ser-473 is prevented by inhibitors of Ptdlns 3-kinase, this residue may be phosphorylated by a distinct 3-phosphoinositide-dependent protein kinase (PDK2 - Fig 7). However, the Ser-473 kinase does not appear to be the PtdIns(3,4,5)P3- dependent peak-1 activity from heparin-Sepharose (Fig 2B), because this enzyme also phosphorylates PKB at Thr-308 (data not shown). The peak- 1 may be a proteolytic fragment of peak-2 (or vice versa) or another isoform of PDKl. It is also possible that PtdIns(3,4,5)P3/PtdIns(3,4)P2 activates the Ser-473 kinase indirectly. For example, the phosphorylation of Ser-473 may be dependent on the binding of PtdIns(3,4,5)P3/PtdIns(3,4)P2 to the PH domain of PKB [18, 21] (but see below). Alternatively, the Ser-473 kinase may be activated by PDKl . The mechanism by which insulin induces the activation of PKBα is shown schematically in Fig 7. The activation of PDKl by PtdIns(3,4,5)P3 is extremely specific, because only D-enantiomers of PtdIns(3,4,5)P3 are effective and many other Ptdlns phospholipids are inactive. Although the enantiomeric configuration of the glycerol moiety is not important, the presence of one or more unsaturated fatty acids greatly influences the extent of activation of PDKl by PtdIns(3,4,5)P3 analogues (Fig 6). Since unsaturated fatty acids discourage tight packing of adjacent phospholipid molecules, it is possible tiiat this arrangement allows for more efficient interaction between membrane-inserted PtdIns(3,4,5)P3 and its effectors, perhaps explaining for the first time the biological significance of the unusual fatty acid composition of inositol phospholipids. PtdIns(3,4,5)P3 and/or PtdIns(3,4)P2 have no effect on the activity of PKBα under conditions where these inositol phospholipids activate PDKl strongly (Fig 6) consistent with our previous findings [18]. This observation, together with the finding that the activation of PKBα by insulin or IGFl results from its phosphorylation at Thr-308 and Ser-473 [15], appears to exclude direct activation of PKBα by 3-phosphoinositides as a mechanism for its activation in vivo. Our results disagree with recent reports which have claimed that PKBα is activated directly by PtdIns(3,4)P2 [19-21]. Contamination of PKBα preparations with PDKl activity may explain this discrepancy; recall that the activation of phosphorylase kinase by cyclic AMP [22] was later shown to result from contamination with a separate cyclic AMP-dependent protein kinase [23] . It has also been reported that PKBα is inhibited by PtdIns(3,4,5)P3 [20,21], but none of the four PtdIns(3,4,5)P3 derivatives we tested inhibited die basal PKBα activity at all, while all four were capable of activating PDKl. It is possible that the synthetic PtdIns(3,4,5)P3 used in [20, 21] contains impurities that inhibit PKBα and or PDKl. Although PKB is not activated directly by PtdIns(3,4,5)P3 or PtdIns(3,4)P2, it does bind these inositol phospholipids witii micromolar affinity [18, 21], via die N-terminal pleckstrin homology (PH) domain [18, 21] . In contrast, PKB binds PtdIns(4,5)P2 with a 10-fold lower affinity and does not bind to otiier inositol phospholipids tested [18, 21]. These findings raise several interesting possibilities. Firstly, the interaction of PtdIns(3,4,5)P3 and/or PtdIns(3,4)P2 with PKB may alter its conformation in such a way as to facilitate phosphorylation by PDKl and the Ser-473 kinase. Secondly, the formation of PtdIns(3,4,5)P3 and/or PtdIns(3,4)P2 in die plasma membrane may recruit PKB to this membrane also facilitating its activation by PDKl and the Ser-473 kinase. However, neither of these mechamsms appear to be essential for the activation of PKB in vivo, because a mutant lacking the PH domain can still be activated at least as well as wild-type PKB in response to insulin [24, 25]. Alternatively, recruitment of PKB to the plasma membrane could be a mechanism for facilitating the phosphorylation of membrane- bound PKB substrates. However, it should be noted tiiat we purified PDKl from the cytosol of skeletal muscle. It will clearly be important to examine whetiier PDKl localises to the plasma membrane when cells are stimulated witii agonists which trigger a rise in the concentration of PtdIns(3,4,5)P3 and PtdIns(3,4)P2. Example 2: Cloning of PDKl We obtained die amino acid sequences of 9 peptide derived from PDKl that we purified from rabbit skeletal muscle, these were: LDHPFFNK; (SEQ ID No 6) ANSFVGTAQYVSPELL; (SEQ ID No 4) AGNEYLIFQK; (SEQ ID No 5) AHPFFESVTWENLHQQTPPK; (SEQ ID No 11) SGSNIEQYIHDLDSNSFELDL; (SEQ ID No 12) QAGGNPWHQFVENNLILK; (SEQ ID No 13) QLLLTEGPHLYYVDPVNK; (SEQ ID No 14) TFFVHTPNR; (SEQ ID No 15) YQSHPDAAVQ; (SEQ ID No 16) We then put these sequences through the BLAST ncbi database search on the Internet and we discovered that all of these 9 peptide sequences were encoded by 2 EST sequences. The information regarding these EST sequences available from the Internet is given in Figures 8 and 9. We then requested the ESTs from the UK HGMP Resource Centre, I.M.A.G.E. Consortium, Hinxton, Cambridge CB1 1SB, UK (a consortium part funded by the Medical Research Council). We then determined the nucleotide sequences of the EST clones ourselves by sequencing both DNA strands of the ESTs. There were a number of errors in the EST sequences available on the Internet. From the data we obtained it is clear that the EST sequences represent two overlapping clones of PDKl. Most of the open reading frame of PDKl was derived by interogation of the dbest database at die National Centre for Biological Information. A full length cDNA clone for PDKl was isolated by hybridisation screening of a cDNA library, in die vector λZAP, made from the human breast cancer cell line MCF7 (a gift of P. Mitchell, Institute of Cancer Research, Sutton, UK). The PDKl probe for the screening was generated by RT- PCR with the primers CTGAGCCAGTTTGGCTGC (SEQ ID No 17) and ACGTCCTGTTAGGCGTGTGG (SEQ ID No 18) corresponding to nucleotide 1138-1567 of the PDKl sequence, with MCF7 cDNA as template. DNA sequencing was carried out on an Applied Biosy stems 373A DNA automatic sequencer using the Taq dye terminator cycle sequencing kit. The nucleotide and amino acid sequences for PDKl (SEQ ID Nos 1 and 2) are shown in Figure 10. The sequence encodes a 556 residue protein witii a predicted molecular mass of 63.1 kDa. We expressed PDKl protein with a Myc epitope Tag in 293 cells (see Examples below) and it migrates as a 68-70 kDa band, and PDKl antibodies we have raised recognise a 69 kDa band in 293 cell lysates (data not shown). For this reason, and because the initiating methionine lies in a good Kozak consensus sequence, the sequence shown in Figure 10 is likely to represent the whole of PDKl . Polynucleotides containing a full length coding sequence for PDKl are readily obtained by, for example, using suitable PCR primers based on the nucleotide sequence given in Figure 10 and amplifying the PDKl cDNA from a suitable cDNA library or from reverse-transcribed mRNA. Also a polynucleotide containing a coding sequence for PDKl is obtained by ligating appropriate portions of IMAGE clone 626511 and IMAGE clone 526583 following digestion witii suitable restriction endonucleases or by using PCR-based strategies for joining appropriate aparts of IMAGE clone 526583 and IMAGE clone 626511. It will be appreciated tiiat a full length coding sequence for PDKl can readily be obtained from a suitable cDNA library using the sequence information given in Figure 10 to generate a probe and tiiat the sequence of any clone obtained in this way can be determined using die Sanger dideoxy sequencing method. The human ESTs encoding PDKl were isolated from many different human tissues (Table A below) indicating tiiat PDKl is expressed ubiquitously. Interestingly, the nucleotide sequence of PDKl possessed 100% identity to the partial sequence of a gene that has been mapped to a 700-kb region on Human Chromosome 16p 13.3 close to the genes responsible for polycystic kidney disease type 1 and tuberous sclerosis type 2 disease [23] . This gene is known to be expressed as a large 8-kb transcript in heart, brain, placenta, lung, skeletal muscle, kidney and pancreas [23] . Table A. List of overlapping Expressed Sequence Tags in the database encoding for PDKl gene. Accession numbers are from gene bank. The tissue is the tissue from which the EST was derived from. Accession Number Tissue AA186323 HeLa cells H97903 melanocyte AA018098 retina AA018097 retina AA019394 retina AA019393 retina N22904 melanocyte W94736 fetal heart EST51985 gall bladder N31292 melanocyte AA188174 HeLa cells AA100210 colon R84271 retina AA121994 pancreas Example 3: Alternative cloning strategy for PDKl The 67 kDa band corresponding to PDKl was cleaved with trypsin and the digest chromatographed on a Vydac C18 column to resolve the tryptic peptides. The sequences of the following three peptides were established: 1. ANSFVGTAQYVSPELL (SEQ ID No 4) 2. AGNEYLIFQK (SEQ ID No 5) 3. LDHPFFVK (SEQ ID No 6) These peptides are homologous to sequences found in die catalytic domains of other protein kinases. Peptide 1 is homologous to a region of subdomain VIII, peptide 2 to a region of subdomain X and peptide 3 to a region of subdomain XI. These sequences are used to clone PDKl using standard PCR-based strategies. Polymerase chain reactions (PCR) are carried out using the following oligonucleotides coding die peptides 1 and 3 (or slight variations thereof; for example the position I may be inosine or various combinations of G, C, A and T): 5'TTTGT(G/T)GGIACIGCICA(A/G)TA(T/C)GT 3' (SEQ ID No 19) coding for the part of peptide 1 shown in boldface type. 5 ' TTIAC(A/G) AA(A/G) A AIGG( A/G)TG( A/G)TC 3 ' (SEQ ID No 20) coding for peptide 3. The resulting PCR fragment contains the region coding for peptide 2 and is analysed by Southern blotting and hybridisation with the following oligonucleotide coding for peptide 2 (or slight variations thereof: for example the position I may be inosine or various combinations of G, C, A and T): 5'AA(T/C)GA(A/G)TA(T/C)(C/T)TIAT(T/C/A)TT(TC)CA(A/G)AA3' (SEQ ID No 21) Positive PCR fragments are subcloned and used to screen skeletal muscle and otiier cDNA libraries to isolate a full length clone for PDK-1. The full-length clone for PDK-1 is sequenced using the Sanger dideoxy method. The rabbit PDK-1 cDNA may be obtained first and this is used to screen a human skeletal muscle cDNA library to isolate a full-length human PDK-1 cDNA. Molecular biology techniques used are essentially as described in Sambrook et al (1989) Molecular cloning, a laboratory manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York. Example 4: Further alternative cloning strategy for PDKl Antibodies are raised against PDKl purified as described in Example 1. The antibodies are used to screen a λgtl 1 expression library made from cDNA copied from human or rabbit skeletal muscle mRNA. Positive clones are identified and the insert sequenced by the Sanger method as in Example 2. Example 5: Expression of human PDKl and activation of PKBα: homology to Drosophila DSTPK61 In order to elucidate the role of PDKl in vivo and to determine the mechanism by which it is regulated by PtdIns(3,4,5)P 3 and PtdIns(3,4)P 2 it was clearly useful to first determine the structure of this enzyme and the mechanism by which PtdIns(3,4,5)P3/PtdIns(3,4)P2 stimulates PDKl to phosphorylate PKB. In this and previous Examples, we describe the cloning, sequencing and expression of human PDKl , and demonstrate that the expressed enzyme activates PKBα in vitro in an identical manner to PDKl purified from muscle. PDKl also activates PKBα in cotransfection experiments and it also potentiated die phosphorylation of Thr308 induced by IGFl . Surprisingly, PDKl was found to be structurally and functionally homologous to the Drosophila protein kinase DSTPK61 , which has been implicated in die regulation of sexual development in Drosophila. Materials and Methods Materials All phospholipids were obtained from the sources described previously [21]. Glutatiiione Sepharose, the pGEX-3X expression vector and 1 ml heparin-Sepharose column (HiTrap) were purchased from Pharmacia (Milton Keynes, UK); monoclonal antibodies 12CA5 and 9E10 were from Boehringer Mannheim (Lewes, UK) and alkylated trypsin and the pSP72 cloning vector from Promega (Southampton, UK). GST-PKBα and sources of all other materials are described in [21] . The pCR 2.1-TOPO cloning vector was from Invitrogen (Leek, Netherlands). Buffer solutions. Buffer A: 50 mM Tris/HCl pH 7.5, 1 mM EDTA 1 mM EGTA, 1 % (by vol) Triton X-100, 1 mM sodium orthovanadate, 10 mM sodium /3-glycerophosphate, 50 mM NaF, 5 mM sodium pyrophosphate, 1 μM microcystin-LR, 0.27 M sucrose, 1 mM benzamidine, 0.2 mM phenylmethylsulphonyl fluoride (PMSF), 10 μg/ml leupeptin, 0.1 % (by vol) 2-mercaptoethanol. Buffer B: 50 mM Tris/HCl pH 7.5, 0.1 mM EGTA, 0.03% (by vol) Brij-35, 0.27 M sucrose, 0.1 % (by vol) 2-mercaptoethanol. Preparation of DNA expression constructs encoding GST-PDK1, Myc- PDKl. Two overlapping human ESTs encoding PDKl (GenBank accession numbers A A 121994 and A A 186323 corresponding to nucleotides 98 to 708 and 467 to 1811 of PDKl (Fig 1) were obtained from the I.M.A.G.E. consortium [42] and sequenced. The two sequences were joined together by an S al restriction enzyme digest of each EST clone, and the appropriate restriction fragments obtained from these digests were ligated to generate a plasmid containing a continuous PDKl sequence from nucleotides 154 to 1670. This construct was used as a template for a PCR reaction to generate an N-terminal epitope-tagged Myc-PDKl (amino acid residues 52-556) construct. This was achieved using the oligonucleotides GCGGAGATC GCCACCATGGAGCAGAAGCTGATCTCTGAAGA GGACTTGGACGGCACTGCAGCCGAGCCTCGG (SEQ ID No 22) and GCGGGGTACCTCACTGCACAGCGGCGTCCGGGTG (SEQ ID No 23) that incorporate a Bglll site (underlined) and a Kpnl site (double underlined). The resulting PCR fragment was subcloned into die Bgl l/Kpri sites of an pSP72 cloning vector, and the nucleotide sequence confirmed by DNA sequencing. The Myc-PDKl coding sequence was subcloned from this vector as a BgHl-Kp fragment into the BamHI and Kpnl sites of the eukaryotic expression vectors pEBG2T [43] in order to generate a construct for the expression of GST-PDK1 in 293 cells. The same fragment was ligated into the Bglll and Sail sites of the vector pCMV5 [44] to generate a construct for the expression of Myc-PDKl in 293 cells. The structure of each construct was verified by DNA sequencing, and plasmid DNA for transfection was purified using the Qiagen plasmid Mega kit according to the manufacturer's protocol. N-terminal Myc epitope tagged PDKl constructs encoding the full length protein (residues 1 to 556) and lacking the PH domain (residues 1 to 450) were generated by a PCR approach using the full length full length PDKl cDNA isolated from die MCF7 library. This was achieved by using the 5' primer gcggagatctgccaccatggagcagaagctgatctctgaagaggacttggccaggaccaccagccagc tgtatgacg (SEQ ID No 24) (for both the full length and ΔPH-PDK1 constructs) and the 3' primers gcggggtacctcactgcacagcggcgtccgggtg (SEQ I D N o 2 3 ) ( f o r f u l l l e n g t h P D K l ) a n d gcggggtacctcagtgccaagggtttccgccagcctgctt (SEQ ID No 25) (for the ΔPH- PDKl construct). The resulting PCR fragments were cloned into the pCR 2.1-TOPO vector and subsequently subcloned into the pEGB-2T vector as BgRl-Kpn fragment and pCMV5 as an EcoRI-Kpήl fragment. A full length catalytically inactive PDKl construct in which Asp223 was changed to Ala was created by the PCR-based megaprimer strategy (Tao & Lee (1994) In: Griffin & Griffin (eds) PCR Technology: Current Innovations, CRC Press, Boca Raton, Florida, pp 69-83) and tiien subcloned into pCMV5 and pEBG-2T as described above. The structure of each construct was verified by DNA sequencing, and plasmid DNA for transfection was purified using the Qiagen plasmid Mega kit according to the manufacturer's protocol. A bacterial expression vector for GST-DSTPK61 was prepared by ligating a EcoK /EcoKV fragment of the Dstpkόl cDNA derived from pBluescriptSK into the EcoRl/Sall sites of the pGEX-3X expression vector. Preparation of DNA expression constructs encoding GST-ΔPH-PKBα. A PCR based strategy was used to prepare a GST-ΔPH-PKBα (encoding residues 118-479 PKBα) construct using as a template a full length human PKBα construct that was isolated from a human skeletal muscle cDNA library and subcloned into the pBluescriptSK vector. The GST-ΔPH- PKBα construct was obtained using the 5 ' primer cgggatccatggacttccggtcgggctca and 3' primer was the T7 oligonucleotide of pBluescriptSK vector. The resulting PCR fragment was cloned into pBluescriptSK as a BamEI-Kpnl fragment, and subsequently into pEBG- 2T as a Bamϋl-Kpnl fragment. Expression of GST-PDK1, GST-ΔPH-PDK1, GST-D223A-PDK1, GST- ΔPH-PKBα and GST-DSTPK61. Twenty 10 cm diameter dishes of human embryonic kidney 293 cells were culmred and each dish transfected with 20 μg of DNA encoding either GST-PDK1 (residues 52-556), GST- PDK1 (residues 1-556), GST-ΔPH-PDK1 , GST-D223A-PDK1, or GST- ΔPH-PKBα using a modified calcium phosphate method [20] . 24 h after transfection, the cells were serum starved for 16 h and each dish of cells lysed in 1 ml of ice-cold Buffer A. The 20 lysates were pooled, centrifuged at 4°C for 10 min at 13,000 x g and die supernatant incubated for 60 min on a rotating platform with 1 ml of glutatiiione-Sepharose previously equilibrated in Buffer A. The suspension was centrifuged for 1 min at 3000 x g, the beads washed three times with 10 ml of Buffer A containing 0.5 M NaCl, and then a further 10 times with 10 ml of Buffer B to ensure complete removal of all the Triton X-100 which interferes with the activation of GST-PKBα by PDKl [21] . GST-PDKlα was eluted from the resin at ambient temperamre with three 1 ml portions of Buffer B containing 20 mM glutatiiione pH 8.0. The combined eluates (0.8 mg/ml protein) were divided into aliquots, snap frozen in liquid nitrogen, and stored at -80 °C. Between 0.5 and 2.0 mg of each GST-fusion protein was obtained and was more than 90% homogeneous as judged by SDS polyacrylamide gel electrophoresis. E. coli transformed with an expression plasmid encoding GST-DSTPK61 were grown at 37 °C in LB medium to an absorbance of 0.6 at 600 nm. Isopropyl-/3-D-thiopyranoside was added to 30 μM and the bacteria were incubated for 16 h at 25 °C before centrifuging for 10 min at 4000 x g. The bacteria were resuspended in 15 ml of Buffer A and lysed by sonication for 4 min on ice. The suspension was centrifuged for 30 min at 30 000 x g and the GST-DSTPK61 was purified by affinity chromatography on 1 ml of glutathione-Sepharose as described above for GST-PDK1. The GST-DSTPK61 derived from this (0.35 mg/ml) was divided into aliquots, snap frozen in liquid nitrogen and stored at -80°C. Assay of GST-PDKl and GST-DSTPK61 activity. GST-PDKl and GST-DSTPK61 were diluted appropriately in Buffer B containing 1 mg/ml bovine serum albumin, and assayed for their ability to activate and phosphorylate GST-PKBα [21] . One unit of PDKl activity was defined as that amount required to increase the basal activity of GST-PKBα by 1 unit of activity in one min. One unit of GST-PKBα activity was that amount of enzyme required to catalyse die phosphorylation of 1 nmol of the peptide RPRAATF (SEQ ID No 1) in 1 min in an assay containing 0.1 mM RPRAATF (SEQ ID No 1) [45]). In order to ensure that die assay was linear with respect to time the concentration of GST-PDKl or GST- DSTPK61 was below 2 U/ml. At this concentration the level of phosphorylation of PBKα was < 0.4 mol phosphate per mol protein in the 30 min assay. Transfection of 293 cells with HA-tagged PBKα and Myc-PDKl. Human embryonic kidney 293 cells were culmred on 10 cm diameter dishes and transfected with 2 μg/ml pCMV5 DNA constructs encoding for HA-PKBα or HA-PKBα plus Myc-PDKl [20]. After 24 h the cells were deprived of serum for a further 16 h and then stimulated for 10 min with either 100 ng/ml IGFl or Buffer. The cells were lysed in 1.0 ml of ice- cold Buffer A, the lysate centrifuged at 4°C for 10 min at 13,000 x g and HA-PKBα immunoprecipitated from aliquots of the supernatant (10 μg protein) [20] and assayed for PKBα with the peptide RPRAATF (SEQ ID No 1) [45] as described previously [20]. 32 P-labelling of 293 cells transfected with HA-PKBα or Myc-PDKl. This was carried out essentially as described previously [20] . Briefly, 293 cells were transfected with HA-PKBα, or with HA-PKBα plus Myc- PDKl, washed with phosphate free DMEM, incubated for 4 h with [ 32 P]- orthophosphate (1 mCi/ml), then stimulated witii IGFl (50 ng/ml) for 5 min. The cells were lysed, and die HA-PKBα immunoprecipitated (using 10 μg of 12CAS antibody per 10 cm dish of cells) or the Myc-PDKl immunoprecipitated (using 10 μg of 9E10 antibody per 10 cm dish of cells). The immunoprecipitated protein was alkylated with 4- vinylpyridine, subjected to SDS/polyacrylamide gel electrophoresis, digested witii trypsin and analysed by chromatography on a C 18 column (Alessi et al (1996) EMBO J. 15, 6541-6551). Results PDKl is a human homologue of the Drosophila DSTPK61 protein kinase. The catalytic domain of PDKl spans residues 83-342 (Fig 10) and contains all of the classical kinase subdomains I-XI [24] . It is most similar to the subfamily of protein kinases that include PKA (39% identity to the catalytic domain), PKC (35 % identity to the ξ isoform) and PKB (35 % identity). The PDKl catalytic domain was even more similar to two yeast protein kinases of unknown function. The catalytic domain was 53 % identical to the S. pombe protein kinase with GenBank accession number 1431588 and 48 % identical to the S. cerevisiae protein kinase with accession number 1078290. However, there was no homology between PDKl and these yeast protein kinases outside of the catalytic domain. In contrast, the Drosophila protein kinase named Drosophila Serine/Threonine Protein Kinase-61 (DSTPK61 , accession number Y07908 ref 22) was not only 54% identical to PDKl in the catalytic domain, but was very similar in the non catalytic C-terminal domain (Fig 11). This homology was most striking between residues 450 and 550 of PDKl where the identity to DSTPK61 was 61 % (79% similarity). These observations suggested that DSTPK61 might be a Drosophila homologue of PDKl . However, DSTPK61 contains a 60 residue C-terminal C- terminal extension not found in PDKl and there is little homology between the N-terminal 70 residues of PDKl and N-terminal 150 residues of DSTPK61 (Fig 11). PDKl also lacks the polyglutamine insertion sequence present near the N-terminus of DSTPK61 (residues 120-150) and a further polyacidic insertion located between subdomains VII and VIII (residues 312 to 370) of the kinase domain (Fig 11). The physiological role of DSTPK61 will be considered further under Discussion. PDKl and DSTPK61 possess a C-terminal Plecktrin Homology domain. The high level of sequence conservation between PDKl and STK61 , from residues 450-550 of PDKl (Fig 11), suggested that this region is likely to have an important function. Inspection of these sequences indicated that these are likely to form part of a Plecktrin Homology (PH) domain. These domains of — 100 residues are found in over 70 other proteins and are predicted to fold into a similar 3- dimensional strucmres and may mediate protein-lipid, protein-protein interactions, or both [25,26] . We have performed sequence alignment of residues 450-550 in both PDKl and STK61 , together with sequences from PH domains of determined tertiary sructure, plecktrin, spectrin, dynamin, and phospholipase C-δ and also with 71 other known PH domain sequences (data not shown). Although the percentage identity is poor between PH domains in general there are certain positions that show high levels of residue type conservation. For PDKl and DSTPK a single position (Tryptophan, position 113, position Trp-535 of PDKl) shows complete identity throughout the domain family, however there are also many similar amino acids at defined regions of the PH domain) (Figure 17). Secondary structure predictions also indicated tiiat residues 450-530 of PDKl (positions 1-80) are likely to contain regions of /3-sheet, while the residues between 531-550 (positions 80-100) are likely to form an extended α-helix, a prediction that is consistent witii the known strucmres of other PH domains [25,26]. Expression of GST-PDKl and GST-DSTPK61. Residues 52-556 of PDKl were expressed in human embryonic kidney 293 cells and residues 1-752 of DSTPK61 in E. coli as fusion proteins with glutatiiione S- transferase (GST) at the N-terminus (hereafter termed GST-PDKl and GST-DSTPK61), and botii were purified on glutathione-Sepharose. The GST-PDKl preparation showed two bands with apparent molecular masses of 87 and 85 kDa (Figure 18, Lane 1) and 2 mg of GST-PDKl purified protein was obtained from 20 (10 cm diameter) dishes of cells. The GST- DSTPK61 preparation showed a diffuse band at die expected molecular mass (105 kDa) together with a number of minor degradation products (Figure 18, Lane 2). 0.35 mg of GST-DSTPK61 were obtained from 0.5 litres of bacterial culture. GST-PDKl and GST-DSTPK61 activate and phosphorylate PKBα in a PtdIns(3,4,5)P 3 or Ptdlns (3, 4) P 2 dependent manner. GST-PDKl and GST-DSTPK61 bom activated and phosphorylated GST-PKBα in die presence of a vesicle background containing phosphatidylcholine (PtdCho) and phosphatidylserine (PtdSer) provided that PtdIns(3,4,5)P 3 or PtdIns(3,4)P 2 were included. The extent of activation of GST-PKBα correlated with the extent of phosphorylation (Fig 12), and no activation or phosphorylation occurred if PtdIns(3,4,5)P 3 or PtdIns(3,4)P 2 were replaced by either PtdIns(4,5)P 2 or Ptdlns 3-P (Fig 12). Identical results were obtained using purified PDKl from rabbit skeletal muscle and full length GST-PDKl (residues 1-556) expressed in 293 cells ([21] and data not shown). A catalytically inactive GST-PDKl mutant in which Asp223 was changed to Ala did not phosphorylate or active GST-PKBα in the presence of PtdCho/PtdSer lipid vesicles containing PtdIns(3,4,5)P3 (data not shown). The specific activities of GST-PDKl (residues 52 to 556, 78 000 U/mg) and GST-PDKl (residues 1 to 556, 89 000 U/mg) towards GST-PKBα in the presence of PtdIns(3,4,5)P3 were similar to PDKl purified from rabbit skeletal muscle (100 000 U/mg), being over 200 times higher than that of bacterially expressed GST-DST PK61 (280 U/mg). Further work is needed to establish whether this difference is caused by misfolding of DSTPK61 or lack of an important post- translational modification when it is expressed in E. coli, or whether DSTPK61 does not recognise human PKBα as well as human PDKl . Some activation and phosphorylation of GST-PKBα was obtained using very high concentrations of GST-PDKl or GST-DSTPK61 in the absence of PtdIns(3,4,5)P 3 or PtdIns(3,4)P 2 . However, the activity of PDKl was enhanced about 1000-fold in the presence of these inositol phospholipids. In the presence of PtdIns(3,4,5)P 3 lipids and at high GST-PDKl and GST- DSTPK61 concentrations, the phosphorylation of GST-PKBα reached 0.75 mol phosphate per mol protem and was paralleled by a 35 fold increase in activity. This was similar to the maximal activation of GST-PKBα obtained using PDKl from rabbit skeletal muscle [21]. Expressed PDKl and DSTPK61 phosphorylate PKBα at Thr308. 32 P- labelled GST-PKBα that had been maximally phosphorylated with either GST-PDKl (Fig 13 A) or GST-DSTPK61 (Fig 13B), was digested with trypsin and chromatographed on a C 18 column. One major 32 P-labelled peptide was obtained in each case. This peptide eluted at 25 % acetonitrile at the same position as the 32 P-labelled tryptic phosphopeptide containing Thr308 [20,21], and contained phosphothreonine and, when subjected to solid phase sequencing, 32 P-radioactivity was released after the first cycle of Edman degradation, confirming that this peptide is indeed that of PKBα phosphorylated at Thr308 (data not shown). PKBα is activated by cotransfection with PDKl in 293 cells and phosphorylated at Thr308. In order to determine if PDKl was capable of activating PKBα in a cellular context, we transfected a haemaglutinnin epitope-tagged PKBα (HA-PKBα) into 293 cells, eidier alone or together with Myc-epitope tagged PDKl (Myc-PDKl). As reported previously, HA-PKBα possessed a low basal activity when transfected alone into 293 cells, which was increased 40-fold after stimulation with IGFl (Fig 14, [20]). However, when 293 cells were transfected witii both HA-PKBα and Myc-PDKl, the activity of HA-PKBα was increased 20-fold in unstimulated cells, and 70-fold after stimulation witii IGF-1 (Fig 14). When 293 cells were transfected with HA-PKBα and a catalytically inactive mutant of PDKl (Myc-D223A-PDK1), HA-PKBα was not activated significantly (Figure 14). In order to establish the mechanism by which overexpression of PDKl in 293 cells induced the activation of PKBα, the cells were incubated witii 32 P-phosphate, stimulated with buffer or IGFl and 32 P-labelled HA-PKBα was immunoprecipitated from the lysates. After digestion with trypsin, the resulting peptides were analysed by C 18 chromatography (Fig 15). As observed previously HA-PKBα is phosphorylated at Ser-124 and Thr-450 in unstimulated cells, and IGFl stimulation induces the phosphorylation of Thr308 and Ser473 (Fig 15 A and 15C). In contrast, when cotransfected with PDKl , HA-PKBα became partially phosphorylated at Thr308 in unstimulated 293 cells, to a level tiiat was 70% of that observed in IGFl -stimulated cells transfected witii HA-PKBα alone. This phosphorylation of Thr308 was increased a further 4-fold in response to IGFl (Fig 15). Importantly, cotransfection of Myc-PDKl with HA-PKBα did not induce phosphorylation of HA-PKBα at Ser473 in unstimulated cells, nor did it potentiate die level of Ser473 phosphorylation following IGFl stimulation (Fig 15). Role of the PH domain in the activation of PKBα by PDKl. A mutant GST-PKBα mutant lacking the PH domain (GST-ΔPH-PKBα, residues 118-479) possessed a 3-fold higher basal activity than that of full length wild-type GST-PKBα was activated (Fig 16 A) and phosphorylated (data not shown) by PDKl in a PtdIns(3,4,5)P3 independent manner. However, the rate of activation was reduced about 20-fold compared to wild-type GST-PKBα (Fig 16A). PDKl purified from rabbit skeletal muscle extracts also activated and phosphorylated GST-ΔPH-PKBα in a PtdIns(3,4,5)P3 independent manner (data not shown). A PDKl mutant lacking the putative C-terminal PH domain was expressed as a GST-fusion protein in 293 cells (GST-ΔPH-PDK1 , residues 1-450). We found that this form of PDKl was still able to activate GST-PKBα in a PtdIns(3,4,5)P3-dependent manner, but the rate of activation was reduced about 30-fold compared to full length wild-type GST-PDKl (Fig 16B). As observed with PDKl purified from rabbit skeletal muscle (see Example 1) or full length GST-PDKl (data not shown), GST-ΔPH-PDK1 was activated more effectively by the D-enantiomer of -sτt-1-stearoyl, 2- arachidonyl PtdIns(3,4,5)P3 than by the D-enantiomer of sn-1,2- dipalmitoyl D-PtdIns(3,4,5)P3, and no activation was induced by the L- enantiomer of -sn-1-stearoyl, 2-arachidonyl PtdIns(3,4,5)P3 (Fig 9B). In contrast sn-l ,2-dipalmitoyl D-PtdIns(3,4)P2 was very poor at inducing the activation of GST-PKBα by GST-ΔPH-PDK1 (Fig 9B) under conditions where this lipid was as effective as s«-l,2-dipalmitoyl D-PtdIns(3,4,5)P3 at stimulating GST-PKBα activation by either full length GST-PDKl (data not shown) or PDKl purified from rabbit skeletal muscle (see Example 1). PDKl is not activated or phosphorylated by IGFl. 293 cells were serum starved for 16h, stimulated witii IGFl lysed and the endogenous PDKl activity present in the cell lysates was determined after chromatography on heparin-Sepharose (see Methods). IGFl stimulation of cells for up to 10 min did not result in any activation or inhibition of PDKl activity (data not shown). In order to see if IGFl stimulation was inducing die phosphorylation of PDKl , 293 cells were transfected with Myc-PDKl (encoding residues 52 to 556), incubated with 32 P-phosphate, stimulated witii buffer or IGFl for 5 min and 32 P-labelled Myc-PDKl was immunoprecipitated from the lysates. After digestion with trypsin, the resulting peptides were analysed by C 18 chromatography. These experiments demonstrate that PDKl is phosphorylated at four tryptic peptides (only on serine residues) in unstimulated cells and that IGFl does not alter the phosphorylation of any of these peptides (data not shown). Treatment of PDKl purified from rabbit skeletal muscle with high concentrations of the serine/threonine- specific protein phosphatase 2 A and protein tyrosine phosphatase IB also had no effect on activity (data not shown). One of die in vivo phosphorylation sites on PDKl was identified as Ser-241 which lies in the equivalent position to Thr308 of PKB in the kinase domain. Discussion PDKl purified 500,000-fold from skeletal muscle [21] contains three proteins with apparent molecular masses of 85 kDa, 67-69 kDa and 45 kDa, and in this Example we established mat the 67-69 kDa component is PDKl, and is likely to be a monomeric protein since it migrates with an apparent molecular mass of 70 kDa on gel filtration (data not shown). When cloned and expressed in 293 cells, this protein activated PKBα and induced its phosphorylation at Thr308, activation and phosphorylation both being dependent on PtdIns(3,4,5)P 3 or PtdIns(3,4)P 2 . PDKl also activated PKBα in cotransfection experiments and potentiated the phosphorylation of Thr308 by IGFl . These observations and the finding that, like PKB, the mRNA encoding PDKl is expressed in every tissue examined (Table A) are consistent with the notion that PDKl lies "upstream" of PKB in vivo. PKBα becomes phosphorylated at Ser473 in vivo, as well as at Thr308, in response to insulin or IGFl . Moreover the phosphorylation of Ser473 is essential for the full activation of PKBα and, like die phosphorylation of Thr308, is prevented by worrmannin [20]. Importantiy, PKBα did not become phosphorylated at Ser473 when cotransfected witii PDKl, and nor did transfection with PDKl affect the level of Ser473 phosphorylation after stimulation by IGFl . These experiments demonstrate that the protein kinase which phosphorylaes PKBα at Ser473 is not activated by PDKl, that phosphorylation of T308 of PKBα in a cell does not cause PKBα to autophosphorylate at Ser-473, and that the requirement for PtdIns(3,4,5)P 3 /PtdIns(3,4)P 2 to trigger the phosphorylation of Ser473 is conferred by a different mechanism. It is of interest that PDKl lies in the same subfamily of protein kinase as PKB. Moreover, like PKB, it also contains a PH domain although, in contrast to PKB, this is located C-terminal to the catalytic domain [13] . The PH domain in PKB is capable of binding PtdIns(3,4,5)P 3 and PtdIns(3,4)P 2 at micromolar concentrations [27,28], which may facilitate its translocation to the plasma membrane that occurs in response to IGFl [29] or interleukin-2 stimulation of EL4-IL-2 cells [30] to form a signalling complex. However, the finding presented in this paper that PDKl is not activated by IGFl , and that a mutant of PKBα lacking the PH domain is activated and phosphorylated independently of PtdIns(3,4,5)P3 (Fig 16A), demonstrates mat the PtdIns(3,4,5)P3-induced activation of PKBα by PDKl is substrate directed, at least in part. It is possible that the binding of PtdIns(3,4,5)P3 to the PH domain of PKBα, alters the conformation of PKBα so that Thr308 becomes accessible for phosphorylation by PDKl . Consistent with this model, deletion of the PH domain of PDKl resulted in an enzyme that is still able to activate and phosphorylate PKBα in a PtdIns(3,4,5)P3 dependent manner (Fig 16B). However, the rate of activation of PKBα by PDKl is reduced 30-fold when the PH domain of PDKl is deleted. Thus it remains possible that the PH domain of PDKl binds PtdIns(3,4,5)P3 and tiiat this greatly enhances the rate of activation of PKBα. PtdIns(3,4,5)P3 can only stimulate the activation of PKBα by PDKl when it is presented in lipid vesicles containing phosphatidyl choline and phosphatidyl serine (Example 1), and a PDKl mutant lacking the PH domain may not be able to interact with lipids and hence be unable to penetrate these vesicles efficiently. This may account for the greatly reduced rate at which PDKl lacking the PH domain activates PKBα. PKBα lacking the PH domain is also presumably unable to penetrate lipid vesicles and this may explain why this mutant is phosphorylated at a 20-fold lower rate by GST-PDKl than fall length PKBα (Fig 16A). Although PKBα is activated by cotransfection with PDKl in 293 cells, the overexpression of PDKl does not potentiate the activation of PKBα by IGFl (Fig 14). The reason is that the activation of PKBα also requires phosphorylation of Ser473, and phosphorylation of Thr308 and Ser473 have synergistic effects on activity (Alessi et al (1996) EMBO J. 15, 6541- 6551). An important finding made in the present smdy is tiiat PKBα does not become phosphorylated at Ser473 when cotransfected with PDKl , and nor does transfection with PDKl affect the level of Ser473 phosphorylation attained after stimulation with IFG1. These experiments demonstrate that the protein kinase which phosphorylates PKBα at Ser473 is not activated by PDKl , and that phosphorylation of PKBα at Thr308 in a cellular context does not cause PKBα to autophosphorylate at Ser473. Like the phosphorylation of Thr308, Ser473 phosphorylation is prevented by incubating cells with wortmannin prior to stimulation with insulin or IGFl . It will be interesting to know whether the Ser473 kinase is activated by PtdIns(3,4,5)P3 or whether the binding of PtdIns(3,4,5)P3 to PKBα alters its conformation to permit phosphorylation by the Ser473 kinase. PDKl was found to be homologous to DSTPK61 a Drosophilia protein kinase which is involved in the regulation of sex differentiation, oogenesis and spermatogenesis of the fruit fly [22] . The identity between PDKl and DSTPK1 was 54% in the catalytic domain, but even greater (61 % identity) in the putative PH domain (Fig 11), further suggesting an important functional role for the PH domain of PDKl . DSTPK61 expressed in E. coli also activated human PKBα and phosphorylated it specifically at Thr308 in a PtdIns(3,4,5)P 3 /PtdIns(3,4)P 2 -dependent manner (Fig 12). These findings indicate that DSTPK61 is a Drosophila homologue of PDKl and suggest that one of its roles may be to activate the Drosophila homologue of PKB (termed DPKB) that was identified several years agao [31 ,32] . Although it is not yet known what the physiological roles of DSTPK1 are in flies the findings presented in this paper suggest that DPKB may lie downstream of DSTPK in signalling pathways regulating sex differentiation and oogenesis [22] . Since Ptdlns 3-kinases are known to play a major role in the activation of PKB in mammalian cells [4-6 and 13] it is likely that a Drosophila phosphomositide 3-kinase (Ptdlns 3- kinase) also plays an important role in the activation of DPKB. Again very little is known about the role of Ptdlns 3 kinase in flies [33] . Only one smdy has been published to date to address this issue in which a Drosophila Ptdlns 3-kinase catalytic subunit termed Dpi 10 has been overexpressed in the wing and eye imaginal dises of Drosophila, in a normal, a constitutively active and a dominant negative form [34]. The results of these studies showed that Ptdlns 3-kinase is likely to play a role in regulating cell growth [34]. Interestingly, loss of function mutations in the Drosophila homologue of the insulin receptor, Inr also inhibited cell growth in imaginal discs and resulted in much smaller than wild type flies [35]. Taken together these results suggest that Drosophila Ptdlns 3- kinases might be important targets of the insulin receptor, perhaps by acting through DPKB may regulate cell growth. The DSTPK61 gene is differentially spliced in male and female Drosophila [22] . This generates many different transcripts that all have the same open reading frame, and therefore produce the same protein, but differ significantly in their 5' and 3' untranslated regions. This is likely to result in different levels of expression of the DSTPK61 protein in male and female Drosophila [22] . In view of the role of PKB in regulating apoptosis in mammalian cells (see introduction) it is possible that the function of DSTPK61 during oogenesis, spermatogenesis and in female adults in relation to sex-determinants might be related to cell survival or cell death decisions. One could imagine the low level of the non-sex specific transcript of DSTPK61 being responsible for general growth function consistent with the role of overexpression of Dpi 10 in cells [34] and the specifically spliced forms seen in female carcasses and ovaries and male testes being controlled translationally leading to die generation of high levels of protein at specific times. It should be remembered that the extent and duration of activation of the MAP kinase cascade is critical in detei-rnining whether a signal induces the proliferation of PC 12 cells or their differentiation to a sympathetic neurone like phenotype [36,37]. Similarly, different levels of expression of DSTPK611 are likely to affect the extent and duration of activation of PKB in vivo and hence may determine the precise fanction of this kinase cascade. There are two signalling pathways involved in sex differentiation where such a situation may operate. The first involves the development of a specific adult male muscle in the abdomen required for holding the female fly during mating [38]. This muscle only develops in males in response to an unknown signal generated by adjacent nerve cells. It is likely that a signalling pathway which causes muscle cells in that region of the female fly to apoptose, whereas in male flies the growth of these muscle cells is promoted [38]. The second pathway involves an unknown signalling mechanism that operates between the somatic cells and germ cells in the male and female gonads in which a signal derived from the somatic cells initiates a signalling pathway that promotes cell survival of germ-line cells and induces these to differentiate into sperm and oocytes [39,40]. The mediators of both of these signalling pathways are at present unknown but, in light of the findings presented in this paper it is possible that a signalling pathway may operate that the unknown signals lead to the activation of Ptdlns 3-kinase, DSTPK and then DPKB and the role of this pathway could be to mediate cell survival by inhibiting apoptosis. To understand the function of these signalling pathways future work will have to concentrate in obtaining mutants of the Drosophila DSTPK61 , PKB and Ptdlns 3-kinase genes, as well as identifying the specific signals that switch on these pathways. It would be of considerable interest to compare the effects of expressing constitutively active and domainant negative forms of Inr, Dpi 10, DSTPK61 and DPKB during oogenesis, spermatogenesis and sex-specific muscle differentiation. Summary Background. The activation of protein kinase B (PKB, also known as c- Akt) is triggered within minutes of cells being stimulated with insulin or growth factors and results from its phosphorylation at Thr308 and Ser473. The activation of PKB and its phosphorylation at both residues are prevented by inhibitors of phosphomositide 3-kinase, and we recently identified and purified a protein kinase that phosphorylates PKB at Thr308. This enzyme only phosphorylated PKB in the presence of lipid vesicles containing phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P 3 ] or phosphatidylinositol 3,4-bisphosphate [PtdIns(3,4)P 2 ] and was therefore termed PtdIns(3,4,5)P 3 -dependent protein kinase-1 (PDKl). Results. We have cloned and sequenced human PDKl. The 556 residue, 63.1 kDa enzyme comprises a catalytic domain (residues 83-344) that is most similar to the subfamily of protein kinases that include PKA, PKB and PKC, and possesses a C-terminal pleckstri homology (PH) domain (residues 450-550). The gene encoding PDKl is located on human chromosome 16p 13.3 and is ubiquitously expressed in human tissues. Human PDKl is highly homologous to the Drosophila protein kinase DSTPK61 , which has been implicated in the regulation of sex differentiation, oogenesis and spermatogenesis in the fly, with 54% identity between the catalytic domains and 61 % identity between die PH domains. GST-PDKl expressed in 293 cells and GST-DSTPK61 expressed in E. coli were purified to homogeneity by chromatography on glutathione-Sepharose and their properties were found to be indistinguishable from PDKl isolated from rabbit skeletal muscle. In the presence of lipid vesicles containing PtdIns(3,4,5)P 3 or PtdIns(3,4)P 2 , but not PtdIns(4,5)P 2 or PtdIns(3)P, GST-PDKl and GST-DSTPK61 both phosphorylated GST-PKBα stoichiometrically at Thr308 and increased its activity 35-fold in vitro. Myc-epitope-tagged human PDKl also activated HA-tagged PKBα 20-fold in cotransfection experiments in 293 cells, and potentiated the IGFl -induced phoshorylation of HA-tagged PKBα at Thr308. Overexpression of PDKl in unstimulated 293 cells resulted in a 20-fold activation of PKBα, and potentiated the IGFl -induced phosphorylation of PKBα at Thr308. Experiments in which the PH domains of either PDKl or PKBα were deleted indicated that the binding of PtdIns(3,4,5)P3 or PtdIns(3,4)P2 to PKBα is required for phosphorylation and activation by PDKl . IGFl stimulation of 293 cells did not affect the activity or phosphorylation state of PDKl . Conclusions. PDKl is likely to mediate die activation of PKB by insulin or growth factors. DSTPK61 is a Drosophila homologue of PDKl , suggesting that PtdIns(3,4,5)P 3 and/or PtdIns(3,4)P 2 are likely to play as yet unidentified roles in sex differentiation in this organism. The effect of PtdIns(3,4,5)P3/PtdIns(3,4)P2 in the activation of PKBα is at least partly substrate directed. References for Examples 2 and 5 and Figures 11 to 15 1. Coffer, P. J. and Woodgett, J.R. (1991) Eur. J. Biochem. 201, 475- 481. 2. Jones, P.F. et al (1991) Proc. Natl. Acad. Sci. USA 88, 4171- 4175. 3. Belacossa, A. et al (1991) Science 254, 244-247. 4. Franke, T.F. et al (1995) Cell 81, 727-736. 5. Burgering, B.M.T. and Coffer, P.J. (1995) Nature 376, 599-602. 6. Kohn, A.D. et al (1995) EMBO, J. 14, 4288-4295. 7. Cheng, J.Q. et al (1992) Proc. Natl. Acad. Sci. USA 89, 9267- 9271. 8. Cheng, J.Q. et al (1996) Proc. Natl. Acad. Sci. USA 93, 3636- 3641. 9. Kulik, G. et al (1997) Mol. Cell. Biol. 17, 1595-1606. 10. Dudek, H. et al (1997) Science 275, 661-665. 11. Kauffmann-Zeh et al (1997) Nature 385, 544-548. 12. Khwaja, A. et al EMBO, J. 16, 2783-2793. 13. Marte, B.M. and Downward, J. (1997) Trends Biochem. Sci. (In press). 14. Cross, D.A.E. et al (1995) Nature 378, 785-789. 15. Welsh, G.I. et al (1994) Biochem. J. 303, 15-20. 16. Cohen, P. et al FEBS Lett. (In press). 17. Lefebvre, V. et al (1996) J. Biol. Chem. 271, 22289-22292. 18. Deprez, J. et al (1997) J. Biol. Chem. (In press). 19. Kohn, A.D. et al (1996) J. Biol. Chem. Ill, 31372-31378. 20. Alessi, D.R. et al (1996a) EMBO, J. 15, 6541-6551. 21. Alessi, D.R. et al (1997) Curr. Biol. 7, 261-269. 22. MacDougall, C.N. et al (1997) "A novel serine/threonine kinase gene (dstpkόl) encoding sex-specific transcripts in Drosophila melanogaster" (Submitted). 23. Burn, T.C. et al (1996) Genome Res. 6, 525-537. 24. Hanks, S.K. et al (1988) Science 241, 42-52. 25. Gibson, T.J. et al (1994) Trends Biochem. Sci. 19, 349-353. 26. Shaw, G. (1996) Bioessays 18, 35-46. 27. James, S.R. et al (1996) Biochem. J. 315, 709-713. 28. Freeh, M. et al (1996) J. Biol. Chem. 272, 8474-8478. 29. Ahmed, N.N. et al (1997) Proc. Natl. Acad. Sci. USA 94, 3627- 3632. 30. Andjelkovic, M. et al (1997) "Membrane targeting activates protein kinase B through a phosphomositide 3-kinase phosphorylation on Thr308 and Ser473" (Manuscript submitted). 31. Franke, T.F. et al (1994) Oncogene 9, 141-148. 32. Andjelkovic, M. et al (1995) J. Biol. Chem. 270, 4066-4075. 33. Vanhaesbroeck, B. et al (1997) Trends Biochem. Sci. (In press). 34. Leevers, S.J. et al (1996) EMBO, J. 6584-6594. 35. Chen, C. et al (1996) Endocrinology 137, 846-856. 36. Traverse, S. et al (1994) Biochem. J. 288, 351-355. 37. Marshall, C.J. (1995) "Specificity of receptor tyrosine kinase signalling-transient versus sustained extracellular signal-regulated kinase activation" 80, 179-185. 38. Lawrence, P. A and Johnston, P. (1986) Cell 45, 505-513. 39. Nothiger, R. et al (1989) Development 107, 505-518. 40. Steinmann-Zwicky, M. (1992) Bioessays 14, 513-518. 41. Cuenda, A. et al (1996) EMBO, J. 15, 4156-4164. 42. Lennon, G.G. et al (1996) Genomics 33, 151-152. 43. Sanchez , 1. et al (l 994) Nature 372 , 794-798. 44. Andersson, S. et al (1989) J. Biol. Chem. 264, 8222-8229. 45. Alessi, D.R. et al (1996b) FEBS Lett. 399, 333-338. 46. Thompson, J.D. et al (1994) Nuc. Acid Res. 22, 4673-4680 Example 6: Assay for compounds which activate PDKl An assay is set up with PDKl , GST-PKBα and the PKBα substrate, RPRAATF (SEQ ID No 1), (as described in Example 1) but with no 3- phosphoinositide. No activation of PKBα is observed. Compounds are tested in the assay and those that give rise to activation of PKBα via PDKl are selected for further smdy. Phosphatidylinositol-3,4,5- trisphosphate is used as a positive control. Example 7: Assay for compounds which inactivate PDKl An assay is set up as above except tiiat it includes phosphatidyl-3,4,5- trisphosphate and therefore PDKl is active with respect to phosphorylating PKBα. Compounds are tested in the assay and those that lead to inactivation of PKBα via PDKl are selected for further study. Example 8 The assay is the same as Example 6 except that PKBα is replaced by PKB 3. Example 9 The assay is the same as Example 6 except that PKBα is replaced by PKB7. Example 10 The assay is the same as Example 7 except that PKBα is replaced by PKBβ. Example 11 The assay is the same as Example 7 except that PKBα is replaced by PKBγ. Example 12: Assay for compounds which compete for phosphatidylinositol-3,4.5-trisphosphate-binding of PDKl PDKl is incubated witii radiolabelled phosphatidylinositol-3,4,5- trisphosphate in the presence of a test compound. Binding of the phospholipid to PDKl in the presence of the test compound is compared to die binding in its absence. Compounds which reduce or enhance the binding are selected for further smdy. The assay may also be carried out with non-radiolabelled PtdIns(3,4,5)P3. Example 13: Assay for compounds which activate PDKl An assay is set up with PDKl and p70 S6 kinase. No 3-phosphoinositide need be present. Compounds are tested in the assay and those that activate PDKl (and lead to increased phosphorylation of p70 S6 kinase) are selected. Example 14: Assay for compounds which activate PDKl An assay is set up with PDKl and a PKBα lacking a functional PH domain. No 3 -phosphomositide need be present. Compounds are tested and those that activate PDKl (and lead to increased phosphorylation of PKBα lacking a functional PH domain) are selected. References 1. Coffer, P.J. and Woodgett, J.R. (1991) "Molecular-cloning and characterization of a novel putative protein-serine kinase related to die camp-dependent and protein-kinase-C families" Eur. J. Biochem. 201, 475-481. 2. Jones, P.F. et al (1991) "Molecular-cloning and identification of a serine threonine protein-kinase of the 2nd-messenger subfamily" Proc. Natl. Acad. Sci USA 88, 4171-4175. 3. Belacossa, A. et al (1991) "A retroviral oncogene, AKT, encoding a serine-threonine kinase containing an SH2-like region" Science 254, 244-247. 4. Franke, T.F. et al (1995) "The protein-kinase encoded by die AKT protooncogene is a target of the PDGF-activated phosphatidylinositol 3-kinase" Cell 81, 727-736. 5. Burgering, B.M.T. and Coffer, P.J. (1995) "Protein-kinase-B (C- AKT) in phosphatidylinositol-3-OH kinase signal-transduction" Nature 376, 599-602. 6. Kohn, A.D. et al (1995) "Insulin stimulates the kinase-activity of RAC-PK, a pleckstrin homology domam-containing SER/THR kinase" EMBO J. 14, 4288-4295. 7. Cheng, J.Q. et al (1992) "AKT2, a putative oncogene encoding a member of a subfamily of protein-serine threonine kinases, is amplified in human ovarian carcinomas" Proc. Natl. Acad. Sci. USA 89, 9267-9271. 8. Cheng, J.Q. et al (1996) "Amplification of AKT2 in human pancreatic-cancer cells and inhibition of AKT2 expression and tumorigenicity by antisense RNA" Proc. Natl. Acad. Sci. USA 93, 3636-3641. 9. Cross, D. A.E. et al (1995) "Inhibition of glycogen-synfhase kinase- 3 by insulin-mediated by protein-kinase-B" Nature, 378, 785-789. 10. Welsh, G.I. et al (1994) "Wortmannin inhibits the effects of insulin and serum on the activities of glycogen-synthase kinase-3 and die mitogen-activated protein-kinase" Biochem J. 303, 15-20. 11. Kohn, A.D. et al (1996) "Expression of a constitutively active AKT SER/THR kinase in 3T3-L1 adipocytes stimulates glucose- uptake and glucose-transporter-4 translocation" J. Biol. Chem. 271, 31372-31378. 12. Dudek, H. et al (1997) "Regulation of neuronal survival by the Serine-Threonine protein kinase AKT" Science 275, 661-665. 13. 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Claims: CLAIMS 1. A substantially pure 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα. 2. A substantially pure phosphatidylinositol-3,4,5-trisphosphate- dependent protein kinase according to Claim 1. 3. A protein kinase according to Claim 1 or 2 that phosphorylates protein kinase Bα at Thr-308. 4. A protein kinase according to Claim 1 which activates PKB substantially in the presence of the D-enantiomer of s/2-l-stearoyl-2- arachidonyl phosphatidylinositol 3,4,5-trisphosphate but is not activated substantially in the presence of the L-enantiomer of the said phosphatidylinositol 3,4,5-trisphosphate. 5. A protein kinase according to Claim 1 which is substantially activated by the D-enantiomer of sn-l ,2-dipalmitoyl phosphatidylinositol 3,4,5-trisphosphate or -s?z-l,2-dipalmitoyl phosphatidylinositol 3,4-bisphosphate but is not substantially activated by d e L-enantiomers of the said phosphatidyl inositol phosphates. 6. A protein kinase according to any one of the preceding claims which is not substantially activated by phosphatidylinositol 3,5- bisphosphate or phosphatidylinositol 4,5-bisphosphate or phosphatidylinositol 4-phosphate or phosphatidylinositol 3- phosphate or inositol 1,3,4,5-tettakisphosphate. 7. A protein kinase according to any one of the preceding claims whose activity is substantially unaffected by worrmannin. 8. A protein kinase according to any one of the preceding claims isolatable from rabbit skeletal muscle. 9. A protein kinase according to any one of the preceding claims comprising the peptide sequence ANSFVGT AQ YVSPELL (SEQ ID No 4) or AGNEYLIFQK (SEQ ID No 5) or LDHPFFVK (SEQ ID No 6) or two or more of these sequences or peptide sequences with from 1 to 4 conservative substimtions thereof. 10. A recombinant polynucleotide encoding a protein kinase as defined in any one of Claims 1 to 9, or encoding a variant or fragment or derivative or a fusion of said kinase or a fusion of a said variant or fragment or derivative, provided that the recombinant polynucleotide is not the DNA corresponding to IMAGE clone 526583 or IMAGE clone 626511. 11. A polynucleotide according to Claim 11 which contains no introns. 12. A replicable vector comprising a polynucleotide as defined in Claim 10 or 11. 13. A host cell comprising a recombinant polynucleotide or a replicable vector as defined in any one of Claims 10 to 12. 14. A polynucleotide comprising a fragment of the recombinant polynucleotide of Claim 10. 15. A method of making a 3 -phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα or a variant or fragment or derivative or a fusion of said kinase or a fusion of a said variant the method comprising culturing a host cell as defined in Claim 13 which expresses said 3-phosphoinositide-dependent protein kinase and isolating said 3-phosphoinositide-dependent protein kinase from said host cell culture. 16. A method of isolating a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα the method comprising the steps of (a) obtaining material that contains said 3-phosphoinositide-dependent kinase, (b) obtaining cell free extracts from said tissue which contain said 3-phosphoinositide- dependent protein kinase, (c) fractionating said cell free extract and (d) selecting a fraction from step (c) which is capable of phosphorylating and activating protein kinase Bα in the presence of a 3-phosphoinositide. 17. A 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα or a variant or fragment or derivative or fusion of said kinase or a fusion of said variant or fragment or derivative obtainable by the method of Claim 15 or Claim 16. 18. An antibody reactive towards a protein kinase as defined in any one of Claims 1 to 10 and 17. 19. An antibody according to Claim 18 reactive towards any of the peptides ANSFVGTAQYVSPELL (SEQ ID No 4) or AGNEYLIFQK (SEQ ID No 5) or LDHPFFVK (SEQ ID No 6). 20. A method of identifying a compound that modulates the activity of a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα, the method comprising contacting a compound witii the said 3-phosphoinositide-dependent protein kinase or a variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative thereof and determining whether, in the presence of said compound, phosphorylation and activation of a protein kinase B or phosphorylation of a suitable substrate is changed compared to the activity of said 3- phosphoinositide-dependent protein kinase or said variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative thereof in the absence of said compound. 21. A method according to Claim 20 wherein the compound decreases the activity of the 3 -phosphoinositide-dependent protein kinase. 22. A method according to Claim 20 wherein the compound increases the activity of the 3-phosphoinositide-dependent protein kinase. 23. A method according to any one of Claims 20 to 22 wherein the compound competes with the 3-phosphoinositide. 24. A method according to Claim 23 wherein the compound substantially prevents activation by phosphatidylinositol-3,4,5- trisphosphate or phosphatidylinositol-3,4-bisphosphate. 25. A method according to any one of Claims 20 to 24 wherein the compound binds to a protein kinase B. 26. A method of identifying a compound that mimics the effect of a 3- phosphomositide on a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα, the method comprising determining whether said compound activates a said 3- phosphoinositide-dependent protein kinase or a suitable variant, fragment, derivative or fusion thereof of a fusion of a variant, fragment or derivative so that it can phosphorylate and activate a protein kinase B or phosphorylate a suitable substrate, the activation by said compound being in the absence of a 3- phosphoinositide. 27. A metiiod according to Claim 26 wherein the 3-phosphoinositide is phosphatidylinositol-3,4,5-trisphosphate or phosphatidyl-inositol- 3,4-bisphosphate. 28. A compound identifiable by die method of any one of Claims 20 to 27. 29. A compound according to Claim 28 for use in medicine. 30. A method of modulating in a cell tiie activity of 3 -phosphoinositide- dependent protein kinase that phosphorylates and activates protein kinase Bα or its interactions with a 3-phosphoinositide or with protein kinase B, the method comprising introducing into the cell a compound according to Claim 28. 31. Use of a 3-phosphoinositide-dependent protein kinase tiiat phosphorylates and activates protein kinase Bα, or a variant, fragment, derivative or fusion thereof or fusions of said variants, derivatives or fragments in a screening assay for compounds which modulate d e activity of said protein kinase, or its interactions with a 3-phosphoinositide or with protein kinase B. 32. Use of a 3-phosphoinositide-dependent protein kinase as defined in any one of Claims 1 to 9 for activating a protein kinase B. 33. A method of activating protein kinase B the method comprising contacting said protein kinase B witii a 3-phosphoinositide- dependent protein kinase as defined in any one of Claims 1 to 9. 34. A kit of parts comprising a 3-phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα or a variant, fragment, derivative or fusion thereof or a fusion of said variants, derivatives or fragments and a means for carrying out the method as defined in any of Claims 20 to 27. 35. Any novel 3 -phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα as herein disclosed. 36. Any novel recombinant polynucleotide encoding a 3- phosphoinositide-dependent protein kinase that phosphorylates and activates protein kinase Bα, or a variant, fragment, derivative or fusion thereof or a fusion of a variant, fragment or derivative.

Inventors: ALESSI DARIO RENATO, ALESSI, DARIO, RENATO
Applicants: MEDICAL RES COUNCIL, MEDICAL RESEARCH COUNCIL
Application year: 1998
Main classification: C12N15
IPC codes: C07K16, C12N1, C12N5, C12N9, C12N15, C12Q1