IMPROVED METHOD FOR THE IDENTIFICATION AND CHARACTERIZATION OF INTERACTING MOLECULES USING AUTOMATION

Abstract: The present invention relates to an improved method for the identification and optionally the characterisation of interacting molecules designed to perform two-hybrid screening in a high throughput fashion. The method of the invention relies on a combination of automated steps used to generate and detect clones that express interacting molecules, and to separate positive from false positive clones. The present invention provides for high-throughput interaction screens for the reliable identification of interacting molecules, which in turn can lead to the identification of substances inhibiting said interactions. Such inhibitors can find their use in the formulation of a pharmaceutical composition.

Description: IMPROVED METHOD FOR THE IDENTIFICATION AND CHARACTERIZATION OF INTERACTING MOLECULES USING AUTOMATION The present invention relates to an improved method for the identification and optionally the characterisation of interacting molecules designed to perform two-hybrid screening in a high throughput fashion. The method of the invention relies on a combination of automated steps used to generate and detect clones that express interacting molecules, and to separate positive from false positive clones . The present invention further relates to an array of host cells, where said host cells express interacting or potentially interacting fusion proteins. The present invention further relates to a database containing a novel combination of data on clones that express interacting or potentially interacting molecules, and to the use of such a database in identifying pathways of or networks of protein- protein interactions from biological systems. The present invention further relates to arrays of clones useful for screening for interactions and/or inhibitors, mediators or agonists of such interactions . The present invention further relates to a computer readable memory comprising a data structure representative for information gained from large scale two-hybrid screens, which computer readable memory can be made useful in establishing pathways and/or networks of pathways of molecular interactions in biological systems . The present invention further relates to a kit useful for the investigation of protein-protein interactions, for example the search for an inhibitor of one or several interactions . The present invention provides for high-throughput interaction screens for the reliable identification of interacting molecules, which in turn can lead to the identification of substances inhibiting said interactions. Such inhibitors can find their use in the formulation of a pharmaceutical composition. Protein-protein interactions are essential for nearly all biological processes like replication, transcription, secretion, signal transduction and metabolism. Classical methods for identifying such interactions like co- immunoprecipitation or cross-linking are not available for all proteins or may not be sufficiently sensitive. Said methods further have the disadvantage that only by a great deal of energy, potentially interacting partners and corresponding nucleic acid fragments or sequences may be identified. Usually, this is effected by protein sequencing or production of antibodies, followed by the screening of an expression-library . An important development for the convenient identification of protein-protein interactions was the yeast two-hybrid (2H) system presented by Fields and Song (1989) . This genetic procedure not only allows the rapid demonstration of in vivo interactions, but also the simple isolation of corresponding nucleic acid sequences encoding for the interacting partners . The yeast 2H system makes use of the features of a wide variety of eukaryotic transcription factors which carry two separable functional domains : one DNA binding domain as well as a second domain which activates the RNA-polymerase complex (activation domain) . In the classical 2H system a so-called "bait" protein comprising of a DNA binding domain (GAL4bd or lex A) and a protein of interest "X" are expressed as a fusion protein in yeast ("bait hybrid") . The same yeast cell also simultaneously expresses a so called "fish" protein comprising of an activation domain (GAL4ad or VP16) and a protein "Y" ("fish hybrid") . Upon the interaction of a bait protein with a fish protein, the DNA binding and activation domains of the fusion proteins are brought into close proximity and the resulting protein complex triggers the expression of the reporter genes, e.g. HIS3 or lacZ . Said expression can be easily monitored by cultivation of the yeast cells on selective medium without histidine as well as upon the activation of the lacZ gene. The genetic sequence encoding, for example, an unknown fish protein, may easily be identified by isolating the corresponding plasmid and subsequent sequence analysis. Meanwhile, a number of variants of the 2H system have been developed. The most important of those are the "one hybrid" system for the identification of DNA-binding proteins, the "tri-hybrid" system for the identification of RNA-protein-interactions, the "reverse two hybrid" system, and some systems transferring the 2H approach to cellular systems other than yeast, namely bacterial and mammalian (Li and Hershowitz, 1993; SenGupta et al . , 1996; Putz et al., 1996; Vidal et al . , 1996; Dove et al . , 1997; Fearon et al . , 1992). The classical 2H system for the identification of protein- protein-interaction, has, until today, only been carried out on a laboratory scale. Although recent developments have taken on the challenges in large scale 2H screening (e.g. Bartel et al.,1996), a successful large scale search of interacting proteins, for example on the basis of a library vs. library screen, has not been reported. However, on the laboratory scale, it is only possible to screen for interactions between gene products which are known and/or which are suspected to interact, as the probability of finding an interaction by random chance is less than 10 The true power of the 2H system, namely finding previously unsuspected interactions, and even interactions between previously unknown proteins and protein families, in screening whole genomes, can only be brought forward in a large scale approach for example by whole genome screening. There are several difficulties that need to be overcome in order to effectively perform interaction screens using the 2H system on a large scale. First, when it is desired to search for all possible interactions within a given set of peptides or proteins, it is immanent to the 2H approach that the number of clones to be handled grows with one half of the square of the number of peptides or proteins that are to be investigated, taking duplicates into account. When trying to β -rl Φ H CQ β -. £ rH MH cn P d 0) g υ MH β Φ • H 4-1 , MH β CQ Λ O cd , φ CQ TJ cn g Φ in TJ φ -, f o η rH υ g rH β β β d H Φ β υ • H • Φ Oi CQ rH 0) o SH r-H SH rH Φ cd cd o β β rH -H 4-1 O Λ SH -H φ cd 4-1 A • -, ft ft 4-1 β o cd Oi Cn β » β Oi -H 4-1 -H β TJ CQ 4-1 -rl β Φ cd 4-1 -H SH β β A Φ ■ ri φ 4-1 g cn β β ■ H Φ Φ -H H SH Φ Φ ft & MH Φ 4-1 0 β SH Φ -rl A CQ 4-1 β cn O CQ -H Φ β β Φ -H O 4-1 H n -H O Φ 4-1 SH cn > U ft g ■ ri cd φ 4-> SH A 4-1 -H Φ υ CQ cn 4-1 - l > * -. o β A -H cd O •H •H -H 01 EH Φ g tn ■ ri A A i Φ cn J β TJ 4-1 CQ > g ft S cd CQ 4-1 -rl β B cn ft ■ ri & libraries, are fused to a DNA binding domain and an activation domain, respectively, false positives may arise by several different mechanisms: • A peptide or protein cloned into the bait hybrid might itself have activating properties, activating transcription of a reporter gene independent of an interaction with the fish hybrid (herein: "False Positives Class 1") . • A peptide or protein cloned into the fish hybrid might itself constitute a DNA binding domain, binding to the DNA binding site or to the basal portion of the promoter, activating transcription of a reporter gene independent of an interaction with the bait hybrid (herein: "False Positives Class 2") . • A peptide or protein cloned into the fish hybrid might specifically bind to the DNA binding domain of the bait hybrid, or, vice versa, a peptide or protein cloned into the bait hybrid might specifically bind to the activation domain of the fish hybrid, reconstituting activation of the reporter gene independent of an interaction between the bait and fish proteins. This may include binding to epitope tags fused to the DNA binding domain or activation domain (herein: "False Positives Class 3") . • Certain peptides or proteins are able to bind non- specifically to many different other structures (herein: "Sticky Proteins") . These will result in a large number of positives with one common genetic element. A number of strategies have been previously described which remove some of the above classes of false positives (Allen et al., 1995; Bartel et al . , 1993). • The use of two reporter genes (Bartel et al . , 1993) : One of these genes usually expresses a selectable marker (e.g. HIS3) and the other reporter gene a measurable marker activity (e.g. lacZ) , and the reporter gene promoters usually are different . By scoring positives according to activation of both reporter genes, this allows removal of a certain part of the False Positives Class 2 since an interaction with both of the different promoters is less likely to occur. • The use of selectable markers and preselection (Bartel et al . , 1996) : This method employs replica plating of clones that express one fusion protein from plates containing selective medium corresponding to the selectable marker introduced with the plasmid that encoded said one fusion protein to plates containing selective medium corresponding to a reporter gene product (e.g. LEU2 as selectable marker on plasmid, HIS3 as reporter gene) . Clones that showed growth on selective medium corresponding to the reporter gene product where identified as False Positives Class 1 or Class 2, respectively, and were subsequently not used for interaction mating. • The use of counterselectable genes and preselection (Vidal et al . , 1996a) : Two populations of mating competent yeast host cells of different mating type are provided that contain (a) the bait hybrid plasmid and one counterselectable reporter gene in the population of cells of the first mating type, and (b) the fish hybrid plasmid and another counterselectable reporter gene in the population of cells of the second mating type. When these first and second populations are kept individually under conditions such that expression of said counterselectable reporter gene inhibits the growth of said host cells, False Positives Class 1 and False Positives Class 2 are hypothetically removed. • The use of a second, different bait hybrid protein: Several approaches have been described, all of which are performed on positive clones after scoring of positives: . (a) curing of the bait hybrid plasmid, transfection with a second bait hybrid plasmid containing an unrelated bait protein fused to the same DNA binding domain as in the original bait hybrid plasmid; expression of the reporter gene(s) indicates False Positives Class 2 as well as a Sticky Protein or False Positive Class 3 being fused to the activation domain (Harper et al . , 1993); (b) curing of the bait hybrid plasmid, transfection with a second bait hybrid plasmid containing an unrelated bait protein fused to a different DNA binding domain that binds to a second DNA binding site controlling a second site comprising the β Ul Φ H CQ rH 0 o\ 4-1 4-1 Φ Φ O TJ id g β -H β td X! Φ Cn 0 o Φ 4-1 O SH Φ -H . 4-1 X! β CQ rH A β TJ cn rd LO -. Φ CQ ti β 4-1 td SH H 4J φ β < O > xi TJ Φ ft o MH . SH Φ cd Φ φ td td s XI -H O υ β SH SH 0 -H o MH CQ g SH ti P υ 4J 4-> •H Φ ft 0 SH 4 O > Φ i φ - U 4-1 o υ xi SH β φ MH ft td X! β 4-1 TJ 4-1 CQ CQ MH rd 4-1 rd ft £ . £ SH ft β 4-1 β -. 4-1 β cd φ β -. β 0 β rH β α cn o CQ td -i o SH SH β CQ Φ ι -H Xi rd g β -. Φ TJ β g β rd > -H Φ id β Φ -H β -H φ SH rd β 4-1 O td MH β O 0 X Φ -rH φ > • H 4-1 > SH •H Cn g U > cd 0) o -H O Ti O Φ TJ X! β 4-1 φ A φ 4-1 u Φ A SH -H φ -rl φ SH rd •rl £ 4 β O Φ 4-1 β CQ 4-1 4-1 υ φ •H -. cd r-i A MH & A 4-1 id 4-1 cn SH -. φ o SH id ft o r-i CQ H Φ MH o β id CQ Φ SH Φ o CQ g CQ SH TJ Φ cn tn Φ O Φ A r-i ■ ri β 4-1 rH Ti 4-1 CQ Φ -i ft β 4-1 SH β • β Φ O 4-1 Φ -H β A β Φ td β tn Ul tn id rd o • 0) O SH 4-1 β - • 4-1 Φ td td CQ SH 0 CN β CN β rH MH Φ • r- Φ Φ ω CQ o £_j A β SH rH 0 O - r-i β Φ O SH > -H SH O φ 4-1 MH φ fd o r-i -H Φ -rl cn SH CQ id o & Φ td • ft υ rd A > SH id > Xi CQ Φ O φ β r-i -. MH TJ A Ul cn ϊ SH φ CQ -H A MH β Φ 4-1 β β MH β β U Φ 0 cn SH ft φ SH 4-1 Φ MH O β 4-1 4-1 ■ ri O o SH MH φ o td r-i Φ O TJ Φ > rd • H A 4-1 φ β -rl r-i -rl ft 0) Cn CQ H g r-i td CQ cn rH 4-1 -rl SH rd 4-1 β Cn Φ cn SH 4-1 β O) 4-1 o rd u SH cd β β cn 4-1 A -Q -H o • Φ β SH ■ ri β SH r-i β cn Φ ϋ -rl o -rl ■ ri φ Φ r-i SH ft Ul Q Φ O l ■ ri O β MH A J 5 Oi CQ r-i Φ CQ 4-1 Φ Φ fd > g > MH β Ul CQ O Φ £s β -. β O β β O X 4-1 SH φ β β Ul Φ Φ Ti > Oi β i β -rl ft rd O rd SH ■ ri SH MH CQ >x β o X! CQ φ β SH SH Φ • H SH β β o H υ ft rH O H ti u U Φ ti Φ Φ 4-1 TJ td -1 cd -iH J Φ β MH Φ ft β fd fd rH SH r-i ft Oi 4-1 Q υ β rH Φ β 4-1 β CQ -H o A cn Φ Φ -H MH SH id xi td β X β {3 β ■ ri Oi Φ _ td cd rH β SH Φ A 4J 4-1 Φ o φ SH td β TJ rd SH Ti β A cd Oi -. - t O 4-1 -. •H 0 cn φ Φ 4-1 β β A td β φ -H MH SH β CQ Φ g fd 0 Φ •-i 4-1 r-i CQ 4-1 -rl o U β rH Φ CQ Q φ rd - l β 4-1 SH o Φ O Φ SH g rH υ rd 0 > *, £ u MH CQ β -H O X! MH ft β td X! Φ X! g β O o r-i Φ β r-i o 0 O CQ Φ Φ SH υ o φ Cn rH 4-1 O ft u id Φ CQ SH O cd u g φ Φ 4-1 ft β CQ β β A β r-i Φ β g A ti β Φ υ β β u SH O g β β CJ 1 i β Φ υ SH o CQ 0 φ > β td fd β 0 Φ O SH SH 0 -H φ cn -rl Φ υ β MH φ ri φ -H β CQ ft O CQ -H Φ CQ TJ Φ id & MH Φ id fd SH CQ φ - > 4-1 -H CQ 4-1 β Φ X! Φ Φ 4-1 o Xi Φ υ Φ υ Φ A CQ φ td Φ Φ X! Q CQ O O 4-1 4 MH H Φ 4-1 xi MH 4J CQ υ H Φ β SH i CQ Φ β Φ SH υ υ β υ A β 4-1 o g rd β SH O > Cn -rl O 4-1 • rl Tl -H SH ft Φ X! β td 0 MH Φ 4-1 a TJ cd 4-1 -H β g g MH -H rd ft id ft 4-1 4-1 U -H O MH CQ 4-1 CQ CN o -i 4-1 -H -H o 4J g X SH X ■ rl β CQ β 4-1 O -rl Ul SH β Φ -H 4-1 rH 4-1 MH ft O Φ O CQ Φ Φ A o U β Q -. β 01 ft ϋ SH CQ td Φ r-i O φ TJ Φ o -rl Φ o 01 cn 0 β rl fd 0 4-1 4-1 TJ ft Φ n φ SH SH 4-1 ft -H β r-i - -1 ft -H Φ β φ O) 4-1 Φ • A Φ U TJ υ CQ 4-1 -H id 4-1 4 fi >-ι SH n cn A Φ SH SH β β td T) β XI Q SH fd β rd TJ β β td H SH cd Φ Φ cn 4-1 SH rd rd φ -H > - l ■ ri Tl 4 -rl SH -rH > SH id 0 > O fd ft β CQ Φ Φ ft SH cn TJ • H 4-1 td H φ A X! Φ -H O Ti • H MH SH 0 r-i u SH A g A O β 4-1 ft g β Oi υ 4J 4-1 Φ 4-1 O φ rd 4 SH A CQ rH td Φ O β O ■ ri X! -H U Φ o 0 o β β Xi U Φ xi Φ U Φ -H H υ MH β MH -H O rH o A rd ft J & 4-1 CQ < -H 4-1 rd SH EH SH td ft r-i Φ • CQ β *, 0 td β Φ H Cn td cd TJ Ul 4-1 4-1 φ cd Φ SH r- β - O A td β υ β ti Φ SH A H -H i β O φ 4-1 υ ■ rl -. β id Φ ■ H 0 —0 TJ O 4-1 SH r- rH CQ 4-1 0 -. MH Os xi CQ CQ β o -. Q ti φ MH fd rd TJ cd cd MH -rl Φ CU & β CQ φ -H - CQ - £ rd 4-1 o MH β g O MH φ 4-1 SH TJ « O Φ Φ φ 4-1 cn β Φ Φ > U Φ 4-1 O υ td g O X! fd 0 Φ r*; • Oi υ SH id φ -H > g φ Φ rH O 4-1 ■ H cd β 01 4-1 υ s TJ Φ υ CQ • SH o o rH > Φ 0 i rd ft A TJ cn MH -. g o β β -H TJ O β Cu TJ TJ Φ rd SH CQ Φ β -H 4J A Φ 4-1 CQ td SH Φ -rl g • rl -rl O β MH Φ β O SH β Φ O H rH ft X! ft 4-1 O td X! β β rH SH id TJ tn H υ φ SH 4-1 rH -ri o -rl Xi rd β 4-1 rd g i A *. 4-1 -H -H SH 4-1 SH -H CQ td -H Oi SH J A Φ 4-1 O β TJ 4-1 4-> 4-1 φ CQ -rl 4-1 ■ ri rd SH SH β CQ ft TJ O -H CQ Φ fd td ft CQ Φ β υ cd β SH 4-1 g β 4-1 Φ l φ fd CQ rd 0 Φ MH MH φ β 4-1 Φ ti & MH o CQ *-, r-l > rd φ 4-1 Φ β CQ tn O o g Ul β A SH Φ g ft >, A o O ■ ri β Ti SH O ■ H CQ cd β X! ft rd TJ fe rd Φ SH xi φ 0 -H 4-1 A r-H X ■ ri Φ -H Φ fd A O H Φ -rl ■ H CQ Ti ■ ri MH rH MH 4-1 X! CQ & SH ■ ri A υ Φ u ti β > O 4-1 4-1 Φ 4-1 MH CQ ft X! TJ SH φ β • β 4-1 -ri g TJ β rH id -H CQ -H U o -H X! 0 IQ A -H Φ ft 4-1 ■ ri Φ 4 xi ■ ri φ ti CQ SH o TJ MH i -H φ MH β 4-1 H 4-1 CQ ■ ri 4-1 U SH A 4-1 -rl rd ti 4 β 4-1 X! O Φ O φ Φ 0 -. 4-1 u • Φ φ td Φ 4-1 ■ ri ft β Ti β 4-1 CQ A υ Φ Φ 4-1 MH rH MH r-i 4-1 cn 01 β CQ β MH TJ id Ul MH cn r-i φ ft rH φ TJ fd CQ CQ r-i β 0 cd cn φ SH β TJ A > T! φ TJ CQ o o β β rH β A ti X! A Φ £ A MH td O cn g r-i TJ β φ -rl o φ Cn >*-. β CQ -rl ft td Ul O ■ ri CQ υ id SH o id o 4-1 Φ Φ o φ O TI Φ SH rH *, A β cd β SH r-i -H φ & 4-1 g -H o S o -. ft r-i -H cd -i Oi Ul SH r-i β A ft β SH ■ ri cd Φ Φ cn r-i r-i ti fd Φ MH 4-1 o & φ r-i rH ) TJ o & β ■ ri J υ φ MH fd ti A 2 ro Φ 4-1 Φ Φ td ■ ri 4-1 CQ 4-1 MH 4-1 4-1 H Φ td Φ β g -rl •rl β SH 4-1 φ Φ SH V SH υ β . υ g β -rl SH CQ -H O) ft X! SH -rl MH β 4-1 φ β MH CQ SH CQ A Ul • n O fd O ^ -. g O * φ Ti β TJ 4-1 g 4-1 4-1 TJ O Oi X! O A Xi o β O fd β -H φ Φ cd cn cn SH r-i CQ 4-1 rn Φ -. > CQ -H Φ CQ td rd Ti SH β o cd O g rH TJ > ■ ri td rd O - — - cn g SH . — . Φ g β id oo X Cn Xi β O β -H φ SH β r-i cn -H r-i rd Φ -H TJ rH Φ X! Φ O CQ φ -i xi • rl Oi Φ φ β 4-1 id O O 4-1 4-1 Φ cd td ti 4-1 rd 4-1 Ti id *. 4-1 φ U > υ β β xi rd β β A rH 4-1 rd -rl ι -rl Φ CQ υ 4-1 υ ti φ υ rd td -i -rl g -H • rl Φ -H o r-i CQ SH TJ 4-1 SH -H cd φ β φ ,Q Φ MH TJ g β Ul CQ cn 4-1 SH 0) Φ β Φ -H O Φ υ Φ Φ o rH o CQ SH ti cn ■ H 4-1 > g ft O -rl β O Φ φ -rl Φ cn X! Φ 4-1 4-1 4-1 . 4-1 Tl Xi MH SH X) td - td φ -H cd φ β cn MH φ O ft > > CQ 4-1 β SH 4-1 xi o td J id 4-1 Φ 4-1 MH CQ Ul β β 4-1 0 A Φ -H -H O MH O Φ & 4-1 SH MH xi -H S ti υ g φ β rH β -. Tl Φ Φ g β & o 4-1 - l β β > Φ 4-1 4-1 ft fd • H 4-1 4-> ft -H Φ -rl 4-1 Φ MH o β g - β o -rl g o Φ Φ CQ SH φ CQ U -rl 4-1 SH o . MH 4-1 0 g cn Φ O 4J β cn 0 υ O β cn 4-1 O) rH 4-1 4-1 r-i 4-1 SH rH Φ CQ Φ TJ υ O β Cn TJ -H in rH ■ ri O A id φ r-i ω υ o 4-1 SH rd X β β ft rd r-i O CQ Φ td ft β TJ ft r-i g CQ Tl g β υ T) CQ -ri β cn rd β Φ β O *, MH φ ft r-i 4-1 SH Φ IQ φ O 0 cn g Φ Φ Φ φ Φ Φ O β φ TJ 4-1 φ TJ rl β o r-i CQ l rd β Φ SH -H - — - O g Φ xi > ■ ri SH rH TJ rH MH fd SH -i cd g β rd Φ g β ti TJ H Φ MH -H 4-1 Φ tn O Cn td 4-> ti A -rl u 0 ft β υ φ td A g xi rd id id 0 rH β CQ O β Φ 4-1 CQ cn rH CN rH 4-1 β X! SH Φ O > -. X o -rl rH tn U 4-1 u H X! id o rH Φ ft -H Xi cn β fd H o φ MH ti o MH Φ Φ Φ X! MH Φ β β MH φ β 4-1 rd X! β 4-1 td O rd β 4-1 Φ Ti X! -. ft cn ft ti 0 4-1 4-1 CQ ■ ri O CQ 0 0 Oi 4-1 υ Φ MH β fe 4-1 -H Φ φ -H 0 β υ Φ 4-1 CQ o β ft id rd 4J 4-1 υ xi 4-1 β td -rH g 0 o ft Xi MH > * -* 4-1 xi • H ft SH r-i r-H SH td . rH cn 4-1 4-1 rd TJ β -H J Xi CQ xi i 4-1 -H , X! 4-1 O id 4-1 4-1 X! 4-1 td td rH ft SH cn rd o SH CQ cn Xi O Φ 4-1 4-1 4-1 i-H 4J SH Φ β 4-1 rH Oi Φ CQ Oi -rl td Cn CQ φ Φ 4-1 g u 4-1 Φ 4-1 xi TJ φ rH -H β td -. cd X! O © υ SH β A Oi β td -H £ rH β O Oi -. υ rH Φ -rl o β β 4-1 -H β rd & Φ u Φ β ft 4-1 -H Φ rd O β O 4-1 CQ o A Cn td Φ 4-1 β Φ g O O CQ Φ φ SH g -H 4-1 Φ 4-1 H rH SH *. -H -H -. cn 4-1 β SH Φ β MH υ -Q cn X! ti β -ri ■ ri Φ g Φ Oi Φ 0) Φ 4-1 0 Φ l MH td Φ β Xi r-i CQ 4-1 >i φ υ td X! MH SH •H o -rl >, υ O β 4-1 4-1 β H > β SH υ β SH -rl O β CQ υ 4-1 β ■ ri rd r-i > td SH 4-1 0 id β Oi 4J Ul Φ MH td rd 0 rd A φ o Φ -H -H rd υ -H -H 0 ti > r-i β SH 4-1 Φ CQ 0 o 4-1 Φ Φ > > r-i cd X! n rH β SH φ ω CQ Φ g • 4-1 ft ft -rl fd -H Φ 4-1 X! Φ 4-1 Φ Φ H β r-i ti Oi ■ H -rl O X! •H 4-1 rd O 1 & g - l β - l 0) SH ■ ri β g 4-1 β 4-1 CQ Oi ft fd SH ft o β r-i Φ Φ SH 4-1 4J O H MH Φ φ g rd in A o H • td r-i fd o u -H MH β o • rl A U -H rd Φ xi A rd U O MH β Φ *. o TJ SH ■ H ω CN EH β Φ φ ft Ul o υ rd fe O -H ft X! 4-1 4-1 CQ 4-1 A u υ EH 4-1 rH fd rd 0 CQ SH A positives. This method should, moreover, be suitable for large-scale library vs. library screens using a high- throughput approach. Preferably, this method would be applicable to a range of different host cell systems, such as yeast, bacterial, mammalian, plant and insect cells. Such method could routinely be applied to the identification of pathways of molecular interactions in cellular environments, and the interconnections between such pathways. Ultimately, the identification of molecules involved in interactions that form part of such pathways can be employed in order to pinpoint targets for pharmaceuticals, and very similar techniques can then be applied to the testing of compounds or compound libraries that potentially inhibit an interaction with relevance to a disease state. The solution to said technical problem is achieved by providing the embodiments characterised in the claims. Detailed description of the invention Accordingly, the present invention relates to a method for the identification of at least one member of a pair or complex of interacting molecules from a pool of potentially interacting molecules, comprising: (A) providing host cells containing at least two genetic elements with different selectable markers, said genetic elements each comprising genetic information specifying one of said potentially interacting molecules, said host cells further carrying a readout system that is activated upon the interaction of said molecules; (B) allowing at least one interaction, if any, to occur; (C) selecting for said interaction by transferring host cells or progeny of host cells to a selective medium that allows identification of said host cells upon activation of the readout system; (D) identifying host cells that contain molecules that activate said readout system on said selective medium; (E) identifying at least one member of said pair or complex of interacting molecules. wherein at least one of the steps (A) , (C) or (D) is effected or assisted by automation creating or analysing a regular grid pattern of host cells. Inclusion of an automation step as a feature of the invention has a number of significant advantages as compared to prior art methods that we addressed in more detail below. The terms "identification" and "identifying", as used in accordance with the present invention, relate to the ability of the person skilled in the art to detect positive clones that express interacting molecules from false positive clones due to the activation of the readout system on the selective media and optionally additionally to characterize at least one of said interacting molecules by one or a set of unambiguous features. Preferably, said molecules are characterized by the DNA sequence encoding them, upon nucleic acid hybridization or isolation and sequencing of the respective DNA molecules. Alternatively and less preferred, said molecules may be characterized by different features such as molecular weight, isoelectric point and, in the case of proteins, the N-terminal amino acid sequence etc. Methods for determining such parameters are well known in the art . The term "potentially interacting molecule (s) " , as used in accordance with the present invention, relates to nucleic acids, peptides, domains of proteins or proteins that can be formed upon the transcription and/or translation of genetic information, and which may but are not required to be able to interact with one or more other such nucleic acids, peptides or proteins, together forming a pair or complex of • g Φ 4-1 IQ *. CQ 4-1 β O TJ id φ SH Φ xi 4-1 Oi β ■ H > •ri SH TJ tQ Φ rH β υ Φ rl o g Φ xi 4-1 0 4-1 1 IQ -rl tf IQ - 4-1 Φ β H S Φ β P IQ U 1 Φ Φ SH rH S ft 0 tf g Φ -. X! Oi 4-1 β <j -rl p_j MH 4-1 1 0 o fd £ J SH tf o φ X! 4-> MH 4-1 β O φ -rl g O) MH β φ o •rl X! 4-1 • 4-1 X tn β φ • H o MH rH tn H O & β -> g O td 4-1 o o Oi β u H Φ ft -1 g SH β IQ -H o O Φ J SH > O SH Cn β Q -H rl g id Φ Φ ft X! SH 4-1 Φ T ) TJ J φ -H g β SH fd O β SH tn SH Φ MH Φ MH β o Φ O T β SH •rl φ fd ft 4-1 4-1 -1 β O IQ td Φ Φ > rl β β β Φ IQ H ■ rl • in Φ H β o φ rH 0 g β o -H in β MH φ IQ Φ X! 4-1 MH O , of readout systems is, in accordance with the present invention, also comprised by the term "readout system". Such a combination will provide an additional safe guard for the identification of clones containing interacting partners. In another preferred embodiment, said readout system additionally comprises at least one counterselectable gene. As the biological principle of counterselection is well known in the art, the person skilled in the art may chose from a variety of such counterselectable genes. Preferably, said genes are URA3 , LYS2 , sacB, CANl, CYH2 , rpsL, or lacY. The person skilled in the art will be able to chose the appropriate marker for a given cell system, e.g. URA3 in a yeast 2H system or sacB in a bacterial system. In accordance with the present invention, it is additionally preferred prior to step (A) that a preselection against clones that express a single molecule able to activate the readout system is carried out in or on culture media comprising a counterselective compound, for example 5-fluoro orotic acid, canavanine, cycloheximide, streptomycin or sucrose. It is highly desirable to remove as many False Positives Class 1 and Class 2 as referred to above even before step (A) in order to reduce the total number of false positives that need to be handled in further steps. This can be achieved by counterselection of host cells comprising potentially interacting molecules able to activate a readout system comprising a counterselectable reporter gene as previously described in WO96/32503. In contrast to WO96/32503, however, it has surprisingly been found that when employing the method according to the present invention, it suffices to carry out a single counterselection step against False Positives Class 1. 4-1 TJ β β β TJ O td o Φ TJ -rl to rd rd 4-1 4-1 -rl φ β u H SH -. φ φ fd rd u 4-1 • H Φ SH in φ υ i Φ φ T! Φ 4-1 g β ft rd •rl u IQ H O g ■ H O β SH ti rd rl 4-> o Φ Φ 4-1 Φ ti g 10 id 4-1 O -H ti 4-1 td MH SH Φ tQ SH β β 0 Φ O β β ft r-i rH rd O SH A o u ri O td υ IQ 4-1 U 4-1 rd β ■ H Φ TJ > ■ ri β X! φ H tn IQ 4-1 *. td U td tn id Xi rd g -H g 1 SH Φ IQ 4-1 SH Φ i β td O 4-1 4-1 td X! β Φ 4-1 » H g β Q B> o id o 0 rl SH • rl u β rd Φ 4-1 o β g υ Oi H 10 id Φ β 4-1 ■ H O 4-1 -H rd > φ TJ SH P J β Φ A U H J O J 4-1 O rl β β β CQ CO Φ Φ -rl β > υ O • •H to IQ U g 4-1 Φ g φ •H SH φ g 4-1 tn 0 4-1 0 IQ β β to ^1 >- φ H >x H Ul tn MH l fluorescent, luminescent or colourimetric plate readers such as the Victor II system from Wallace (Finland) . Preselection employing one or more counterselective reporter genes or, alternatively, by visually detecting host cell expressing a single fusion protein able to activate the readout system, can equally be used to remove false positive clones in the 2H system. Using a counterselective reporter gene, however, is in some cases unsatisfactory for a number of reasons, particularly when applied to a large-scale library vs. library screen with the aim of generating protein interaction networks of a eukaryotic system. First, it is known that during counterselection using media containing counterselective compounds such as such as 5-FOA, many yeast cells that express the counterselective marker may not be killed, but rather remain dormant and become viable when transferred to medium free from counterselection. This effect can lead to a "leaky' genetic preselection system which may lead to significant false-positive colonies being found in an interaction library. This is particularly so when a library vs. library screen is conducted, as even a small number of, e.g. false Positives class 1, each of which will activate the readout system regardless of its partner protein, will make the task of finding a small number of true positives next to impossible. Second, because many yeast colonies from a library of cells are of different sizes, each containing a different number of cells, collecting surviving cells by scraping or washing of colonies from a counterselective plate will skew the representation of particular inserts from a cloned and plated library. Third, for many host-cell types including mammalian systems, counterselective genes are not available or are difficult to enable. Finally, the sensitivity of a counterselective approach is low since fusion proteins that are weak auto-activators of the readout system will cause insufficient reporter gene transcription to cause cell death through counterselection. In contrast, the readout system commonly used to finally assay any protein- protein interaction between two fusion proteins in the 2H -1 td ! -1 IQ β 0 l -1 U td SH φ -1 β H β H -1 H 1 l -1 H -1 H H H l ) H x -1 H d -1 «Λ 4-1 TJ 4-1 Φ 4-1 S-i rH If) IQ β SH 4-1 tQ SH . a - 10 o cd - f- MH u rd to © rd φ O to MH β rd 4-1 g *. 10 O φ 0 β O φ g 0 O •rl Φ β H a td -H Φ φ Φ 4-1 rH g rl β 4-1 υ CQ rH i-H φ 4-> 00 Ox 4-1 -H H SH φ Ol φ Φ Φ β •H 4-1 r-H cd Cn SH •H -H H A tα td 4-1 O Φ id o TJ β - SH A fd Φ SH to H 1 Φ β β 4-1 td 4-1 > Φ cd β 10 TJ ω 4-1 , rl 4-1 g MH -H . U EH o > td *. i-H o υ -rl CQ -rl β 0 U -H SH , Φ id Φ SH td O 10 to υ SH β tα -H > to Φ Φ to XI Φ i Φ 1 in Φ 0 IQ to υ -H td TJ β SH 4-1 β ■ H O td • 4 4-1 υ 4-1 MH -. XI i SH CQ 4-> β 4-1 MH β β a. S4 X β o a MH fd o rH g β to IQ fd -H id id id 1 O Φ -H l ^ 4-1 cd β β CQ -H O 4-1 •H id -. β rd -H O X! -rl a u -rl β Φ Xi to 4-1 φ s SH β g X o O φ ti φ β φ > Φ Φ 4-1 β 4-1 4-1 to -rl SH 0 a 4-1 o β xi β 10 rH 10 O -H φ β 0 -H O X! 4-1 ft 4-1 0 A to H β 0 o 4-1 Φ 4-1 -H -. a -H u -H 0 id Φ 4 to to 4-1 -rl ti 4-1 4-1 O fd TJ φ rd θ* SH SH φ -H SH β td O > to 4-1 4-1 g β X! u a Φ to IQ ft β 4-1 SH Φ •H cd β β g Φ O > to 4-1 fd SH z, , o ■ ri u Φ Φ 10 tα TJ 10 *. rl TJ Φ -. TJ Φ Φ CQ ft rH SH φ cd o 4-1 td > 4-1 β β β xi Φ ti u X rd 4-1 4-1 to β φ Φ 1 4-1 H ti to φ cd > rH β XI ft SH υ H id X 0 rd o MH φ 4-1 4-1 g td β Φ SH 10 10 rl Φ MH 4-1 X! φ Φ , — . a rl β XI -H β cd O O xi φ SH u β X β φ 0 *-. fd Φ -H υ 4-1 0) H u cd X 4-1 rl Φ ■ H cd cd O 4-1 SH Φ TJ 4-1 tn O MH φ SH -H tn 0 4 4-1 X! to MH SH β SH rl vo Φ β -rl rl SH Cn -H υ ft X! o Φ ti φ XI φ O X! Φ rd ti o td β υ φ TJ MH cd cd φ (Tx O X ft MH Φ cd in Φ ft 4-1 xi > ** , o 0) rd X 4-1 -H β a 4-1 X! -ri MH J TJ to Cn β O rl β cn to Tl Ul g O MH β 4-1 td 4-1 -H rH fe td rl -H β tα •H xi 4-1 O -ri β fd o o o H rH cd cd φ 4-1 MH φ MH φ 4-1 Φ 4-1 rH O TJ td Φ Ό β SH SH id Φ 4-1 o IQ 4-> 4-1 — rl φ β X TJ SH u TJ Φ O g -H X • β - β • rl β φ 4-1 β -H Φ IQ SH , XI to β 10 υ Φ SH o Φ O ft φ Φ SH tQ -rl TJ td υ β 4 id O tn TJ β fd 4-1 -. to Φ id 10 Φ β Φ rl rH O IQ Xi H rH Cn td 4-1 TJ o r-i Φ > -rl ιd *. SH φ SH 0 SH Φ i φ X! > td r-i TJ rH β cd Φ SH SH 4-1 CQ Φ Oi β SH β ft TJ 4-1 -. to to i-H a tn rl 0 -H A -rH 1 β 4-1 TJ & TJ β X! O 4-1 A Φ O Φ -H CQ β -H 4-1 cd cd Ul o id φ • rl r-H rl 1 β A 4-1 ■ ri SH O o id SH o cd 4-1 to 4-1 -H to td ft rd r-i Oi SH a MH g φ φ -H rH β rl rH rl fd β o td β U H td υ u to Φ β 4-1 SH tQ & X! φ IQ - 9< β φ rl id Φ υ •H • rl rl -H td > 4-1 υ β 4-1 0 0) -H TJ • rl φ cd β Φ -H ft 4-1 Φ SH rH 4-1 g -H Oi td υ U -rl Φ 4-1 • rl ti • -H id Φ o r-H SH rl cd 4-1 -H Xi 4-1 • β β id ^ -H φ id β o £ 4-1 td td - Φ 10 rd J MH 4-1 φ TJ SH 4-1 a cd cd Oi cd & EH & 0 10 g Φ O TJ MH 4-1 MH 0 rl υ O u > φ 4-1 > Φ o υ SH φ a & TJ cd > o β o 4-> β φ in φ » φ SH o ■ H -H 4-1 SH -rl fd SH β β > β Oi β SH 10 id O -H -H X! O • X! -H 4-1 td CO u 4-1 CQ A φ 4 ti 4-1 a MH O -ri >*, -rl o 10 TJ o Φ TJ 4-> > 4-1 4-1 ■ rl g TJ cd 10 TJ cd o to g u φ • H rd o tn -H 4-1 MH SH SH SH β MH -H β O Φ o υ O 4-1 Φ CO o Oi > * . -H SH β Φ o IQ TJ φ >> -H Φ TJ o Φ β td TJ & Φ o O 4-1 β Xi XI TJ _ φ cd 4-1 υ 4-1 φ X! id IQ CQ to ft -H 4-1 4-1 Φ td TJ rH ti g o β SH -rl SH φ g Q υ υ fd 4-1 φ Φ r-H φ CQ O 4-1 o φ id CQ > φ << υ td rl o g Φ Φ XI 4-1 -H g Φ β g Φ o SH rl φ o CQ rl > * ". 0 φ β 4-1 4-> δ SH Oi φ id β X rl to φ Xi 4-1 -H υ β Φ A β g 4-1 cd a CO 4-1 cd Φ CQ rH g O β U td td CQ > X! φ • β 0 Φ rl SH EH 0 rl β β β rl MH SH Φ g φ Ul U -H o td 4-1 rl td A CQ ti υ - td rd SH TJ td -H TJ rd SH g Cn cd SH φ TJ φ TJ CO id 4-1 J rl 1 ■ ri φ rl xi tn 4-1 Φ - a SH β • a -. β Φ X! H 4-1 rl Φ -H X a rH Φ ti -H -H u cd id 4-1 B 4 id g SH 10 φ Φ o 4-> to o g Cn £ β id -rl X! cd φ XI TJ ft S-I J CQ φ Φ Cn tn • H td υ rl φ O β g SH A > -rl id rl β g υ o SH O Xi g 4-1 H rl O cd -H XI id rl SH 1 O CQ -H -H rl 4-1 β TJ φ o 4-1 Φ 4-1 xi φ -H φ SH id TJ & 4-1 -H o υ rl SH 4-1 > CO t 1 β φ eq X! 4-1 Oi -rl in -H Φ 4-1 MH £ id 4-1 > φ 4-1 Φ MH r-H φ to cd 0 IQ o -rl X! ■ ri β l Φ *. β o & , Ti υ IQ o O H -rl 4-1 tn XI 4-1 4-1 Φ X! 10 υ fe TJ β SH X! 1 Φ O φ xi SH MH rH Φ H in β 0 4-1 4-1 in in β 4-1 o . 4-1 Φ id -i , Ol β -H o -H a 4-1 O SH -H ti 4-1 o O rl SH 0 CQ rl SH Ul β β β o o SH tn o -H xi SH A rl β φ a • X! φ £ Φ 4-1 ft td Φ -rl g u υ a fd -H • rd ■ ri φ ±j MH 4-1 φ • rd rH 0 φ 4-> 4-1 4-1 CQ 4-1 4-1 Xi id φ ft Φ •H MH Ox A Φ -H β Ti > rH SH 4-1 a a rl Φ β 10 rH td X! SH 4-1 to Φ O -H υ •H Oi 4-1 fe Cn 4-1 MH O If) 4-1 4-1 ■ ri TJ • rl φ in rH 4-1 rd to -. td Ti β X! Φ φ -ri -H 4-1 υ cd g ti β β TJ 4-1 β cd O β β -H β IQ o Φ SH rl Φ Φ 1 rl φ 4-1 υ Φ Φ 4-1 Cn id 4-1 rH to Φ Φ a β TJ cd φ β -H > cd fd TJ fO -H Ul 4-1 X! φ r-H υ 4-1 >s SH IQ ■ rl Φ XI -H & > β < SH *. υ 0 β -H X! φ l -H l SH 4-1 β\ in ti a id , ti β 10 to O 0) β & to 4-1 rd id TJ cd -H β -rl 0 rH -H SH Ul 4-1 cd 10 rl Ov 4-1 td φ g A ti u 4-1 0 0 to g 0 TJ Φ 1 4-1 • -rl 10 4-1 0 4-> υ cd ti φ φ υ TJ A td O CQ 4-1 X 4-1 O 1 -rl φ to a υ rH rH rl H r-i β 4-1 Φ to TJ SH φ φ -rl β g Ό MH ti cd i cd β β -rl in 0 to 4-1 0 i-H rd *. rl 4-1 O rl β td o 10 SH XI φ X! φ IQ β IQ rH g Ul MH ft o 0 10 IQ X O SH β & CQ o φ β rl Φ 0 -rl -H 0 Φ H 0 Φ β to *. X! cd φ β 0 cd cd φ -rl X 0 β SH -H Φ xi ft to td 4-1 -rl g *. o Ol u β X! 5 £ J O X! & CO β Xi 4-1 u Cn MH CQ g g TJ TJ φ 4-1 CO Xi td > variety of host-types. Most preferably, this said visual differentiation is effected or assisted by automated systems. Of course, the genetic elements may be engineered and prepared in one host organism and then, e.g. by employing shuttle vectors, be transferred to a different host organism where it is employed in the method of the invention. In another preferred embodiment, the method of the present invention comprises transforming, infecting or transfecting at least one set of host cells of said sets of host cells with said genetic element or genetic elements prior to step (A) . Whereas the person skilled in the art may initiate the identification method of the invention starting from fully transformed or transfected host cells, he may wish to first generate such host cells in accordance with the aim of his research or commercial interest. For example, he may wish to generate a certain type of library first that he intends to screen against a second library already present in said host cells. Alternatively, he may have in mind to generate two or more different libraries that he wants to screen against each other. In this case, he would need to first transform said host cells, simultaneously or successively, with both or all types of genetic elements. In another preferred embodiment, the method of the present invention comprises transforming, infecting or transfecting one set of host cells of said sets of host cells with at least one genetic element prior to step (A) , selecting against host cells in said one set of host cells expressing a molecule able to auto-activate said readout system and transforming, infecting or transfecting said set of host cells with at least one further genetic element prior to step (A) . © TJ • H 0- td - w CQ Ol β υ X! -H 4-1 4-1 -H υ s β SH CQ 4-1 rl 10 H XI Φ O V - tα 4-1 4J 10 β O cd X! B H TJ 0 -H MH td to tα β td - SH 4-1 M β Φ β g 0 -rl β TJ 0 MH η 0 Φ β & Ti td Φ H SH SH φ Φ β MH σ Φ id SH ft ft o σv SH β © If) Φ cd X! •5 4-1 β O - 0 β O td & 0 β SH H Ol ) 00 cd Cu SH • *-- O . υ fe oo 0 H • & 'J* £ 4-1 CD 0 H MH SH 0 0 CQ • H β β φ -H Ol φ O β ti υ & g ■ 4-1 O O cd SH g β -> o ft β -H o 4-1 - -H U β 4-1 id -rl u SH U s Φ 4-1 g* Φ β 0 4-1 -H SH β 0) -H Φ * . β A MH O O H - U β CQ -H β • υ o CQ -rl ■ > g 4-1 o cd Φ Φ β β β -H o η rl «. g υ A O l υ ft o -H SH Φ 4-1 ro H td - σv X! g β σv -H φ H O CQ 4-1 υ CQ CQ 0 O Φ ft O N . • g Φ 4-1 to ι 10 4-1 β o TJ fd Φ SH β -H to β o φ Cn cd β cd > TJ cd φ SH cd Φ -H -H β Φ TJ Ol β • H o a tα SH Φ X! Oi • H X! -. H cd SH Φ β Φ Ol β large scale screening and, hence, preferred. As the person skilled in the art will realise, the choice of said carrier will largely depend on the host cell system under investigation . The selective media used for growth of appropriate clones may be in liquid or in solid form. Preferably, said selective media when used in conjunction with a spotting robot and membranes as planar carriers are solidified with agar on which said spotted membranes are subsequently placed. Alternatively, and also preferably, said selective media when in liquid form are held within microtiter plates and said transfer is made by replication. Referring now to step (D) of the method of the invention, the activation state of the readout system can be analysed by a variety of means. For example, it can be analysed by visual inspection, radioactive, chemiluminescent, fluorescent, photometric, spectrometric, infrared, colourimetric or resonant detection. Preferably, said identification in step (D) of host cells that express interacting fusion proteins from consideration of the activation state of said readout system of host cells grown on the selective medium as specified in step (C) is effected or assisted by automation using visual means . Also preferably, said identification of host cells that express interacting fusion proteins in step (D) from consideration of the activation state of said readout system is effected or assisted by automated digital image capture, storage, analysis or processing. Here, automation includes the use of electronic devices such as computers in conjunction with complex instruction sets such as software, commercially available or self devised, which performs or assists in performing large numbers of calculations on images converted to a digital format. In this embodiment, positive clones which are preferably arrayed on a planar carrier such said nucleic acids are amplified by PCR prior to transfer to the planar carrier. Most preferably said nucleic acid is affixed in a regular grid pattern in parallel with additional nucleic acids representing different genetic elements encoding interacting molecules. As is well known in the art, such regular grid patterns may be at densities of between 1 and 50 000 elements per square centimeter and can be made by a variety of methods. Preferably, said regular patterns are constructed using automation or a spotting robot such as described in Lehrach et al . (1997) and Maier et al . (1997) and furnished with defined spotting patterns, barcode reading and data recording abilities. Thus it is possible to correctly and unambiguously return to stored host cells containing said nucleic acid from a given spotted position on the planar carrier. Also preferably, said regular grid patterns may be made by pipetting systems, or by microarraying technologies as described by Shalon et al . (1996), Schober et al (1993) or ockart et al . (1996). Identification is, again, advantageously effected by nucleic acid hybridisation. Once produced, nucleic acids carried on these arrays can be detected using a variety of methods. Preferably, this method is hybridisation using labelled hybridisation probes . However, other detection methods such as mass-spectrometry may be employed. Said labelled hybridisation probes can be labelled with any detectable moiety including radioactive elements, fluorescent and chemiluminescent molecules, or molecules that can be detected via secondary enzymatic or binding assays. Said hybridisation probe can comprise DNA, RNA or PNA molecules, and may consist of one class of molecule, for example a short oligonucleotide, gene fragment, cDNA clone, genomic fragment or YAC. Also, said hybridisation probe may be a complex mixture of nucleic acids representing the gene-expression state of a given tissue, cell type, or developmental or disease state. Two said complex mixtures of nucleic acids may be used in two separate hybridisation experiments with replica nucleic acid arrays to identify — φ X) H β 0 TJ H β O & IQ td & X! 4-1 fd a β 0 -H 4-1 0 rd SH Φ 4-1 β -H β Φ 4-1 O SH 1 β -H Φ 4-1 O SH , β td interaction library. Finally, if both members of a given interaction have been identified, then it may be that the investigator does not wish to waste further resources on re- isolating the same interaction. Identifying those clones from the interaction library that are hybridisation-positive for both members of a previously identified interaction will enable the investigator to ignore these clones for further work. These embodiments have the advantage of saving the investigator both cost and time. The focused hybridisation approach to identifying interactions based on hybridisation will rapidly identify many interactions making up a protein-protein interaction pathway. Indeed, by identifying most interactions that make up several different protein-protein interaction pathways, it will be extremely probable that two or more pathways will be found to have a particular protein in common. Such pathways can then be combined and hence form part of a network of protein-protein interactions. Therefore, because this approach can efficiently investigate several different protein-protein pathways in parallel, it is highly suitable to the generation of a network of protein-protein interactions . In a further preferred embodiment, the present invention provides for a method further comprising: (F) providing at least one of said genetic elements in step (A) , which additionally comprises or comprise a counterselectable marker, wherein said counterselectable markers are different for each type of genetic element; (G) selecting for interaction by transferring host cells or progeny of host cells, which transfer is optionally effected or assisted by automation in a regular grid pattern, in step (C) to (i) at least one selective medium that allows growth of host cells only in the absence of a counterselectable marker specified in (F) and in the presence of a selectable marker; and (ii) further selective medium that allows identification of host cells upon activation of the readout system; (H) identifying host cells in step (D) that contain interacting molecules that: (iii) do not activate said readout system on said at least one selective medium specified in (i) , and (iv) activate said readout system on said selective medium specified in (ii) ; In a more preferred embodiment, said genetic element that additionally comprises a counterselectable marker further specifies an activation domain fusion protein. As referred to above, false positive clones have proven to dramatically reduce the overall usefulness of the 2H system. For example, by inclusion of a marker counterselecting for the absence of a genetic element that specifies one of a pair of the potentially interacting partners, clones that will grow and therefore only carry the second genetic element specifying the second partner can now be tested for the activation of the readout system. If the clone containing only the fusion protein encoded by the second genetic element activates the readout system in the absence of the other genetic element, then it will be classified as a false positive. Thus, only clones that activate the readout system in the presence of both or all genetic elements, but do not activate the read out system when one of the genetic elements is lost are classified as positives. In order to save time and effort, preferably only the plasmid encoding the activation domain is removed, as the fusion protein comprising the DNA binding domain is more likely to have auto-activating properties. In a further preferred embodiment, the present invention provides for a method further comprising: (I) providing at least two of said genetic elements in step (A) , which additionally comprise different counterselectable markers; (J) selecting for interaction by transferring host cells or progeny of host cells, which transfer is optionally effected or assisted by automation in a regular grid pattern, in step (C) to (v) at least one selective medium, wherein said selective medium allows growth of said host cells only in the absence of the first counterselectable marker of said counterselectable markers as specified in (I) and in the presence of a first selectable marker; (vi) at least one selective medium, wherein said selective medium allows growth of said host cells only in the absence of the second counterselectable marker of said counterselectable markers as specified in (I) and in the presence of a second selectable marker; (vii) a further selective medium that allows identification of said host cells upon activation of the readout system; and (K) identifying host cells in step (D) that contain interacting molecules that : (viii) do not activate said readout system on said at least one selective medium specified in (v) ; and (ix) do not activate said readout system on said at least one selective medium specified in (vi) ; and (x) activate said readout system on said selective medium specified in (vii) In a more preferred embodiment, said at least two genetic elements that additionally comprise a counterselectable marker further specify a DNA binding domain fusion protein and an activation domain fusion protein, respectively. Yet more preferably, said counterselectable marker or counterselectable markers of step (F) or (I) are selected from the group of URA3, LYS2, sacB, CANl, CYH2 , rpsL, lacY, D mu or cytosine deaminase. In a preferred embodiment of the present invention the same test is also applied to the first genetic element, counterselecting for the absence of the second genetic element . When employing the present invention according to this embodiment, only clones that activate the readout system in the presence of both or all genetic elements, but do not activate the read out system when either of the genetic elements is lost are classified as positives. By removing both genetic elements, a maximum number of false positives can be identified. This becomes particularly useful with growing total numbers of clones . The use of the counterselectable system described in this invention compared to the prior art has the advantage that only one strain which expresses the potentially interacting fusion proteins is generated and must be analysed. In contrast, to detect false positive clones using the state of the art yeast 2H system, plasmids that encode fish proteins usually need to be isolated and retransformed into yeast cells harboring plasmids that encode unrelated bait proteins . Further, the enormous number of false positive clones that would be isolated when using the classical 2H system on a large scale, yet are discriminated by the method of this invention no longer precludes an effective high through-put analysis of clones. In the long run, it is expected that the method of the present invention is especially advantageous for a high throughput analysis of a large number of clones containing interacting molecules since many specific interactions and the individual members of these interactions can be identified in a parallel and automated approach. In a further embodiment, the invention provides an array of clones on a produced by automation at a density greater than 5, wherein each clone comprises: (L) a readout system or part of a readout system; and (M) one genetic element or a combination of more than one genetic elements, said genetic element or elements each comprising a selectable marker and genetic information comprising one part of a multipart functional entity fused to one potentially interacting molecule; According to the present invention, such an array may comprise genetic elements specifying known potentially interacting molecules and could be used for screening libraries for interactions with these molecules,- equally, it might comprise genetic elements specifying molecules known to interact with DNA and might be used to screen for inhibitors of these interactions; finally, it might comprise genetic elements specifying a library or libraries of unknown potentially interacting molecules, which could be used to perform 2H screens for interacting molecules. In a further embodiment, the invention provides an array of clones on a carrier not derived from yeast or bacterial cells, wherein each clone comprises: (N) a readout system or part of a readout system,- and (0) one genetic element or a combination of more than one genetic elements, said genetic element or elements each comprising a selectable marker and genetic information comprising one part of a multipart functional entity fused to one potentially interacting molecule. According to the present invention, such an array may comprise genetic elements specifying at least two libraries of unknown potentially interacting molecules and could be used for screening libraries of compounds for inhibition of previously uncharacterised interactions; finally, it might comprise genetic elements specifying a library or libraries of known or unknown potentially interacting molecules, which could be used to perform screens for compounds mediating an interaction between molecules that do not interact in the absence of such compound. Preferably, said arrays of clones comprise genetic elements or combinations of genetic elements which are identical in not more than 10 %, more preferably not more than 5 %, yet more preferably not more than 2 %, most preferably not more than 1 % of clones in the array. In a further preferred embodiment, said arrays of clones comprise genetic elements or at least one of said combination of genetic elements further comprises a counterselectable marker. In a further preferred embodiment, said arrays of clones comprise genetic elements in which at least one part of the multipart functional entity is a transactivating or DNA binding domain. In a further preferred embodiment, said arrays of clones are produced by a picking robot, spotting robot, pipetting system, micropipetting system or fluorescent assisted cell sorting (FACS) system. In a further preferred embodiment, the carrier on which said array of clones is affixed is at least one microtiter plate, porous or non-porous support . In a further preferred embodiment, the at least one microtiter plate containins 96, 384, 846 or 1536 wells. In a further preferred embodiment, the number of different clones in said array is greater than 10000. In a further preferred embodiment, the clones in said arrays of clones are mammalian cells or insect cells or plant cells. In a further preferred embodiment, the invention relates to an array of clones on a carrier, wherein each clone comprises : (P) a readout system; and (Q) at least two genetic elements each encoding a fusion protein comprising one part of a multipart functional entity fused to one interacting molecule, wherein the interaction between the at least two interacting molecules reconstitutes the multipart functional entity, which in turn is able to activate the readout system. According to the present invention, such an array may comprise genetic elements specifying known interacting molecules and could be used for screening compounds or preferably libraries of compounds for inhibitions of interactions known to be represented in the array; equally, it could be used to screen for compounds that strengthen or potentiate an interaction. It is preferable to generate a second re-arrayed regular grid pattern of positive clones after step (E) . The process of re- arraying would be most advantageously done by an automated H td 0 Pi Φ T) td SH 4-1 β -H SH o H rd υ -H ft O 4-1 - ti td rl β υ 10 β g td SH 4-> β -H - CO β o φ β rd 4-1 β u XI β to * corresponding to the URA3 system may be devised by the person skilled in the art on the basis of the teachings of the present invention and are also comprised thereby. Also, the present invention relates to a method for the production of a pharmaceutical composition comprising identifying a further molecule in a cascade of interacting molecules, of which the at least one member of interacting molecules identified by any of the above methods is a part of or identifying an inhibitor of said further molecule. Once at least one member of the interacting molecules has been identified, it is reasonable to expect that said member is a part of a biological cascade. Identification of additional members of said cascade can be effected either by applying the method of the present invention or by applying conventional methods. Also, inhibitors of said further members can be identified and can be formulated into pharmaceutical compositions. In a further embodiment, the invention relates to a Kit comprising at least one of the following: (R) A carrier comprising an array of clones as defined above,- and/or (S) a device allowing access to information on the computer readable memory described above characterising the clones in or on said carrier. Such kit could be used, for example, for the rapid identification of inhibitors of interactions or pathways of interactions, for the identification of pathways that toxic substances act on, or, concomitantly, detoxifying agents and for the identification of interaction pathways. In another embodiment of the present invention, said kit is used to identify interactions that are inhibited by a substance under investigation. Advantageously, those molecules identified by the method of the present invention as interacting with many different molecules can be recorded. This information can reduce the work needed to further characterise particular interactions since those interactions comprising of a molecule found to interact with many other molecules within a 2H system may be suspected of being artifactual (Bartel et al . , 1993). Preferably, the data obtained by using the method of the present invention can be accessed through the use of software tools or graphical interfaces that enable to easily query the established interaction network with a biological question or to develop the established network by the addition of further data. Accordingly, the present invention further relates to a computer implemented method for, storing and analysing data relating to potential members of at least one pair or complex of interacting molecules encoded by nucleic acids originating from biological samples, said methods comprising,- (Y) retrieving from a first data-table information for a first nucleic acid, wherein said information comprises,- (xv) a first combination of letters and/or numbers uniquely identifying the nucleic acid, and (xvi) the type of genetic element comprising said nucleic acid and (xvii) a second combination of letters and/or numbers uniquely identifying a clone in which a potential member encoded by said nucleic acid was tested for interaction with at least one other potential member of a pair or complex of interacting molecules (Z) using said second combination of letters and/or numbers to retrieve from said first data-table or optionally further data-tables, information identifying additional nucleic acids encoding for said at least one other potential member in step (xviii) . A preferred embodiment of said method further comprises :using said second combination of letters and/or numbers in step (xvii) to retrieve from a second data-table further information, where said further information at least comprises the interaction class of said clone, and optionally additional information comprising, (AA) the physical location of the clone; and (BB) predetermined experimental details pertaining to creation of said clone, including at least one of: (xvii) tissue, disease-state or cell source of the nucleic acid; (xviii) cloning details,- and (xix) membership of a library of other clones . It is additionally preferred, that said method comprises using said information of step (Y) on said first and/or of step (Z) on additional nucleic acids to relate to a third data-table further characterising said first and/or additional nucleic acids, where said further characterising comprises at least one of (CC) hybridization data, (DD) oligonucleotide fingerprint data, (EE) nucleotide sequence, (FF) in-frame translation of the said nucleic acids, and (GG) tissue, disease-state or cell source gene expression data; and optionally identifying the protein domain encoded by said first or additional nucleic acids. Preferably also said method comprises identifying whether said potential members encoded by the nucleic acids interact, by considering said interaction class of said clone in which nucleic acids were tested for said interaction in step (xvii) . More preferably, said data relates to one or more of 10 to 100 potential members, yet more preferably 100 to 1000 potential members, yet more preferably, 1000 to 10000 potential members and most preferably more than 10,000 potential members . In a preferred embodiment, said data was generated by the aforementioned method for identifying members of a pair or complex of interacting molecules. In a further preferred embodiment, said interaction class comprises one of the following: Positive, or Negative, or False Positive. It is further preferred, that sticky proteins are identified by consideration of the number of occurrences a given member is identified to interact with many different members in different clones of said positive interaction class. More preferably, said first data-table forms part of a first database, and said second and third data tables form part of at least a second database. Yet more preferably, said second database is held on a computer readable memory separate from the computer readable memory holding said first database, and said database is accessed via a data exchange network. It is further preferred, that said second database comprises nucleic acid or protein sequence, secondary or tertiary structure, biochemical, biographical or gene expression information. In a particularly preferred embodiment, data entry to said first, second or further data tables is controlled automatically from said first data base by access to other computer data, programs or computer controlled robots. It is yet more preferred, that at least one workflow management system is built around particular data sets to assist in the progress of the aforementioned method for identifying members of a pair or complex of interacting molecules. Most preferably, said workflow management system is software to assist in the progress of the identification of members of a pair or complex of interacting molecules using the aforementioned method of hybridization of nucleic acids . In another preferred embodiment, said data are investigated by queries of interest to an investigator. More preferably, said queries include at least one of (HH) identifying the interaction or interaction pathway between a first and second member of an interaction network (II) identifying the interaction pathway between a first and second member of an interaction network and through at least one further member, (JJ) identifying the interaction or interaction pathway between at least two members characterised by nucleotide acid or protein sequences, secondary or tertiary structures, and (KK) identifying interactions or interaction pathways that are different for said different tissue, disease-state or cell source. Yet more preferably, parts of said information are stored in a controlled format to assist data query procedures. Even more preferred is a method, wherein the results of said queries are displayed to the investigator in a graphical manner . Yet more advantageous is the method, wherein a sub-set of data comprising data characterising nucleic acids identified as encoding members of a pair or complex of interacting molecules is stored in a further data-table or data base. Yet more preferably, consideration of the number of occurrences a given member is identified to interact with a second or further member is used to decide if said data characterising nucleic acids form part of said sub-set of data. Even more preferred is the method, wherein additional information or experimental data is used to select those data to form part of said subset. Most preferably, to speed certain data query procedures, the structure in which the data is stored in the computer readable memory is modified. In another preferred embodiment, the data is held in relational or object oriented data bases. The invention further relates to a data storage scheme comprising a data table comprising a data table that holds information on each member of an interaction, where a record in said table represents each member of an interaction, and in which members are indicated to form interactions by sharing a common name . Preferably, in said data storage scheme said common name is a clone name or unique combination of letters and/or numbers comprising said clone name. A computer-implemented method for handling of data gathered provides a robust and efficient solution for handling the large amount of protein-protein interaction data produced by the method of the invention. It provides the ability to communicate with and utilise different data-bases and/or other data storage systems across intra or internets, interfaces to allow querying of the data-base by an investigator and visual display of the results of the query. Relational or object orientated data-bases, with data-parsing and display programs supporting said data-base secures ease of use. By way of example, Figure 2 displays a scheme and features for a set of data-tables suitable for managing such interaction data. The primary links between table-keys are indicated, as are the entry fields or elements to be held within each table. If desired, elements of a table may be expanded into an additional table holding further data. Likewise, certain tables may be expanded into an additional data-base to hold and manage further data. Said additional data-base may be stored on the same or on remote computers. Elements of the table can be recorded in numerical, descriptive or fixed format, whatever is most appropriate for the respective data. To provide efficient querying, where appropriate, elements are recorded in controlled vocabulary. Figure 3 displays in what part of the work process during an interaction experiment each table is most relevant and where it forms the underlying data-set from which work-flow management software for that part of the process is based. . H CO β O -H > Φ SH ft MH O β O 4-1 cd tα -H r-i td u 0 H TJ β fd β o -H 4-1 O β β MH Φ XI 4-> » ! o X! 4-1 φ g to -H X! 4-1 unknown proteins can be predicted by determining their interaction partners. It also can be used to predict the response of a cell to changes in the expression of particular members of the networks. Finally, these data can be used to identify proteins or interactions between proteins within a medically relevant pathway which are suitable for therapeutic intervention, diagnosis or the treatment of a disease. The invention further relates to a method for the identification of at least one member of a pair or complex of interacting molecules, comprising: (T) providing host cells containing at least two genetic elements with different selectable markers, said genetic elements each comprising genetic information specifying one of said members, sat least one of said genetic elements that further specifies an activation domain fusion protein additionally comprising a counterselectable marker, said host cells further carrying a readout system that is activated upon the interaction of said molecules; (U) allowing at least one interaction, if any, to occur; (V) selecting for said interaction by transferring progeny in a regular grid pattern effected by automation to: (xi) at least one selective medium, wherein said selective medium allows growth of said host cells only in the absence of said counterselectable marker and in the presence of a selectable marker; and/or (xii) a further selective medium that allows identification of said host cells only on the activation of said readout system,- (W) identifying host cells containing interacting molecules that: (xiii) do not activate said readout system on any of said selective media specified in (xi) ; and (xiv) activate the readout system on said selective medium specified in (xii) ; and (X) identifying at least one member of said pair or complex of interacting molecules. The figures show: Figure 1 The applications of an established and exhaustive network of protein-protein interactions. The identity of positive clones and the identity of the members comprising the interactions for the entire interaction library are stored in a database. These data are used to establish a network of protein-protein interactions which can be used for a variety of purposes. For example, to predict the existence of new biological interactions or pathways, or to determine links between biological networks. Furthermore with this method, the function and localisation of previously unknown proteins can be predicted by determining their interaction partners . It also can be used to predict the response of a cell to changes in the expression of particular members of the networks. Finally, these data can be used to identify proteins within a medically relevant pathway which are suitable for therapeutic, diagnosis intervention and for the treatment of disease. Figure 2 A scheme and features for a set of data-tables suitable for storing, managing and retrieving data from a large-scale protein-protein interaction screen. The scheme could be implemented in either relational or object-orientated data- bases. The primary links between table-keys are indicated, as are the suggested fields or elements to be held within each table. Figure 3 A process flow representing the experimental and informatic flow during a large-scale protein-protein interaction screen. The figure displays in which part of the experimental steps each table from a the data-base described above is most applicable. Each table forms the underlying data-set from which work-flow management software for that part of the process is based. Figure 4 Plasmids constructed for the improved 2-hybrid system. The plasmid maps of the pBTMllδa, b and c DNA binding domain vector series and the pGAD428a, b and c activation domain vector series . Both plasmids contain the unique restriction enzyme sites for Sal I and Not I which can be used to clone a genetic fragment into the multiple cloning site. The plasmids are maintained in yeast cells by the selectable markers TRPl and LEU2 respectively. The loss of the plasmids can be selected for by the counterselective markers CANl and CYH2 respectively. Polylinkers used within the multiple cloning site to provide expression of the genetic fragment in one of the three reading frames . Figure 5 The structure of the URA3 readout system carried by the plasmid pLUA. Important features of pLUA include the URA3 gene which is under the transcriptional control of the lexAop-GALl promoter, the ADE2 selectable marker that allows yeast ade2-auxotrophs to grow on selective media lacking adenine and the β-lactamase gene (bla) which confers ampicilin resistance in E. coli . The pLUA plasmid replicates autonomously both in yeast using the 2μ replication origin and in E. coli using the ColEl origin of replication. Figure 6 A schematic overview of one embodiment of the method of the invention. For the parallel analysis of a network of protein- protein interactions using the method of the invention, a library of plasmid constructs that express DNA binding domain and activation domain fusion proteins is provided. These libraries may consist of specific DNA fragments or a multitude of unknown DNA fragments ligated into the improved binding domain and activating domain plasmids of the invention which contain different selectable and counterselectable markers. Both libraries are combined within yeast cells by transformation or interaction mating, and yeast strains that express potentially interacting proteins are selected on selective medium lacking histidine. The selective markers TRP1 and LEU2 maintain the plasmids in the yeast strains grown on selective media, whereas CANl and CYH2 specify the counter-selectable markers that select for the loss of each plasmid. HIS3 and lacZ represent selectable markers in the yeast genome, which are expressed upon activation by interacting fusion proteins . The readout system is, in the present case, both growth on medium lacking histidine and the enzymatic activity of β-galactosidase which can be subsequently screened. A colony picking robot is used to pick the resulting yeast colonies into individual wells of 384-well microtiter plates, and the resulting plates are incubated at 30°C to allow cell growth. The interaction library held in the microtiter plates optionally may be replicated and stored. The interaction library is investigated to detect positive clones that express interacting fusion proteins and discriminate them from false positive clones using the method of the invention. Using a spotting robot, cells are transferred to replica membranes which are subsequently placed onto one of each of the selective media SD-leu-trp-his, SD-leu+CAN and SD-trp+CHX. After incubation on the selective plates, the clones which 4-1 Φ TJ o 03 Xi CΛ to Φ • r * - rt 4-1 4-1 e-3 tα rt EH IS] Φ SH +-) φ β . 03 . — . φ CU H β to φ o as φ u Xi MH . Φ o g . in σv SH •5 H O rt SH as φ Φ . as EH O TJ 4-1 id -H β H co CU as ^ J Oi rt Φ • td >< SH X! H β H g β -H -H rl fd as -H rt cn β o β g β >, TJ Cn β rd a TJ -H -H • β -H O 4-1 a O υ TJ β H S Ul id O as -H tα -H φ β 03 β -H 4-1 -H TJ υ TJ Φ 03 -H 0 H o td Oi -H Φ rt — * υ Oi Oi H ti 4-1 td φ -H td Φ -H XI < -J8 0 Φ rt CQ β SH β TJ -H a a SH Oi SH β H g β β Oi ■≥ 1 A 4-1 ti SH β H g β 4-1 J O Si H 4-1 SH TJ cd as •H Φ > -H U β Φ -H ft Φ φ X! -H β £ Φ Φ φ 4-1 0 a 0 td φ • fe a υ β -H Φ g -H Φ TJ -H 4-1 03 Φ XJ X! SH 4-1 TJ 4-1 -H A ft MH to a MH H g IQ -— . 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Φ υ -H 4-1 ro • H SH υ g , O , MH β SH QJ -H O *, g Ol 4-1 υ & rt £ SH 4-1 Ul 0 Φ -H 10 β -H a β Cn H Ti rt -H SH SH SH 4-1 cd Φ > a rd -H H tα φ SH a O ti SH 4-1 -H J -H β H H φ as -H ft Φ Φ 03 4-1 SH -H MH a g J β β Φ SH Φ Φ X Φ Φ Ol SH υ TJ 5 td id -. X! ft > r > ft X! ft rt Cn H Φ TJ 0 o SH to TJ 0) TJ Φ H -* O as g • H β CO β β U Φ -H β -H as 4-1 φ β A β to 0 Φ φ β id Φ SH 03 a φ 4-1 Φ o Φ -H TJ O O -H SH Oi 4-1 -H 0 -H β Φ β X! > SH tα -H g CQ cd β Φ β 4-1 10 IQ H cd Φ -H X! X! O Φ υ Ul β H to • A & XJ -H O id as as g -H SH o 03 as o β 4-1 O 5 - Φ SH as σv TJ -H 4-1 ■ 3 β ^ ~. Ό MH td 4-1 id . Φ A TJ CO A β rt *, XJ TJ o O β fd ft SH >-. H o β 4-1 r- CO O H SH pq TJ XJ *. 4-1 β -H 4-1 O Φ SH TJ to • H H O X! 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O g β to SH g H β β Φ 0 J H Φ H β υ aS 4-1 o 4-1 4-1 rl Φ Φ φ X Φ as aS 0 φ rl SH ft Φ ft o Φ 0 rt ft to rt g c to > & U υ -H O CD 03 a tn CO a IQ , SH φ ti H 0) g ft as rl CQ g O υ SH MH • ,— , m oo cn H — J 4-1 ^ g to rt £ T) β cd o H β Φ <D T) SH φ β φ Oi SH -rl pq fe Digital images of the β-gal assays made from the replica Nylon membranes containing the defined interaction library obtained from the selective media (a) SD-leu-trp-his, (b) SD- trp+CHX and (c) SD-leu+CAN. In each case, The left hand side of each membrane contains control clones and clones from the defined interaction library, and the right hand side contains only clones from the defined interaction library. The two regions marked on the first membrane represent those clones magnified in Figure 11. The overall size of each membrane is 22 x 8 cm and contains 6912 spot locations at a spotting pitch of 1.4 mm. Figure 11 Magnification of clones from the interaction library taken from the same region of three membranes obtained from the selective media SD-leu-trp-his, SD-trp+CHX and SD-leu+CAN assayed for β-gal activity: Clones imaged from a region of the right hand side of the membrane containing the defined interaction library. Clones from the defined interaction library that express interacting proteins are ringed and correspond to the microtiter plate addresses 06L22 and 08N24. Clones imaged from a region of the left hand side of the same membranes containing control clones and clones from the interaction library, where clones around each ink guide-spot are arranged as shown and correspond to: 00 Ink guide spot; 01 False positive control clone that expresses the fusion protein GAL4ad-LexA; 02 False positive clone expressing the fusion protein LexA-HIPl; 03 Positive control clone expressing the interacting fusion proteins LexA-SIMl & GAL4ad-ARNT; 04 Clone from the defined interaction library. The positive control clone (spot position 03) is ringed. Figure 12 A subset of the list of clones identified by computer query of data produced by automated image analysis and Φ > -H 4-1 U Φ ft 03 Φ SH H £ tf 1 r- tf C §D ft Tt β as Figure 15 Readout system ativation for clones in a regular grid pattern from an interaction library. 23 384-well microtiter plates of the sea urchin interaction library were spotted in a "3x3 duplicate' regular grid pattern around an ink guide-spot on a 222 x 222 mm porous membrane (Hybond N+, Amersham, UK) using a spotting robot. The membrane was incubated in SD-leu-trp- his medium for 3 days, assayed for lacZ expression using the β-gal assay as described by Breeden & Nasmyth (1985) and air dried overnight. A digital image was captured using a standard A3 computer scanner. Figure 16 Hybridisation of a gene fragment (Probe A) encoding for Protein A to an array of DNA from an interaction library. The probe was labelled radioactively by standard protocols, and hybridisation-positive clones from the interaction library are identified by the automated image analysis system. The position of clone 5K20, from which the gene fragment was isolated, is indicted. Other hybridisation-positive clones also carry this gene-fragment, and by recovery of interacting members from these clones, a protein-protein interaction pathway for Protein A can be uncovered. Figure 17 A graphical representation of the hybridisation-positive clones generated by hybridisation of Probe A to a DNA array representing the interaction library. Figure 18 A graphical representation of hybridisation- and interaction- positive clones generated by a subsequent hybridisation with probe B (isolated from the clone marked in a grey box) . Also shown, are the positions of the hybridisation-positive clones from probe A. Interaction-positive clones that carry both gene fragments are identified as hybridising with both probes . 03 H H Φ υ Tt Φ β -H aS 4-1 β 0 υ *. J rt φ SH rl as A U -H XJ & ] T! β aS H 03 β o -H 4-1 -H to O ft β o TJ φ 4-> 4-1 O ft 03 from the strains xia and x2a. To assist in recognition of the duplicate spotting pattern, ink was spotted in position 2 directly to the right of the spotted yeast clones, b) The membrane was transferred to a YPD agar plate and was incubated at 30° C overnight to allow interaction mating to occur, c) Diploid yeast cells that had grown on the membrane were subsequently analysed for β-galactosidase activity using the method of Breeden & Nasmyth (1985) . Figure 22 The two vectors constructed to provide further genetic features to enable the method of invention within a prokaryotic two-hybrid system. The vectors are based on the pBAD series of vectors which provide tight inductive-control of expression of cloned genes using the promoter from the arabinose operon (Guzman et al . , 1995 J. Bact . 177: 4141- 4130), and can be maintained in the same E. coli cell by virtue of compatible origins of replication. The plasmid pBAD18- RNAP expresses under the control of the arabiose promoter, fusion proteins between the α amino terminal domain (NTD) of the α-subunit of RNA polymerase and DNA fragments cloned into the multiple cloning site. The presence of this plasmid in kanamycin sensitive cells can be selected by plating on growth medium supplemented with kanamycin, or for its absence by the counterselective rpsL allele by plating on media supplemented with streptomycin (Murphy et al . 1995) . The plasmid pBAD30-cI expresses under the control of the arabinose promoter, fusion proteins between the λcl protein and DNA fragments cloned into the multiple cloning site. The presence of this plasmid in amplicillin sensitive cells can be selected by plating on growth medium supplemented with amplicillin, or for its absence by the counterselective lacY gene by plating on media supplemented with 2-nitrophenyl-β-D- thiogalactosidase (tONPG) (Murphy et al . 1995). Additionally, the oriT sequence enables unidirectional genetic exchange of the pBAD30-cI plasmid and its derivatives from E.coli cells containing the F' fertility factor to F " strains lacking the fertility factor. Examples Example 1: Construction of vectors yeast strains and readout system for an improved yeast two-hybrid system 1.1 Construction of vectors The plasmids constructed for an improved yeast two-hybrid system pBTMllδ a, b and c and pGAD428 a, b and c are shown in Figure 4. Both sets of vectors can be used for the construction of hybrid (fusion) proteins. The vectors contain the unique restriction sites Sal I and Not I located in the multiple cloning site (MCS) region at the 3 " - end of the open reading frame for either the lexA coding sequence or the GAL4ad sequence Figure 4b) . With both sets of plasmids fusion proteins are expressed at high levels in yeast host cells from the constitutive ADH1 promoter (P) and the transcription is terminated at the ADH1 transcription termination signal (T) . The two-hybrid plasmids shown in Figure 4a are shuttle vectors that replicate autonomously in both E. coli and S. cerevisiae . The three plasmids pBTM118 a, b and c are used to generate fusions of the LexA protein (amino acids 1-220) and a protein of interest cloned into the MCS in the correct orientation and reading frame. The plasmids pBTMllδ a, b and c are derived from pBTM117c (Wanker et al . , 1997) by insertion of the adapters shown in Table 1 into the restriction sites Sal I and Not I to generate the improved vectors with three different reading frames. The plasmids pBTM118 a, b and c carry the wild type yeast CAW! gene for counterselection, which confers sensitivity to canavanine in transformed yeast cells (Hoffmann, 1985) . The plasmids also contain the selectable marker TRPl , that allows yeast trpl-auxotrophs to grow on selective synthetic medium without tryptophan, and the selectable marker hia which confers ampicillin resistance in E. coli . The plasmids pGAD428 a, b and c are used to generate fusion proteins that contain the GAL4 activation domain (amino acids 768-881) operatively linked to a protein of interest. The plasmids pGAD428 a, b and c carry the wild type yeast CYH2 gene, which confers sensitivity to cycloheximide in transformed cells (Kaeufer et al . , 1983), the selectable marker LEU2, that allows yeast leu2-auxotrophs to grow on selective synthetic medium without leucine, and the bacterial marker aphA (Pansegrau et al . , 1987) which confers kanamycin resistance in E. coli . The plasmids pGAD428a, b and c were created from pGAD427 by ligation of the adapters shown in Table 1 into the MCS to construct the improved vectors with three different reading frames. For the construction of pGAD427 a 1.2 kb Dde I fragment containing the aphA gene was isolated from pFGlOlu (Pansegrau et al . , 1987) and was subcloned into the Pvu I site of the pGAD426 using the oligonucleotide [B2] adapters 5'- GTCGCGATC- 3' and 5' -TAAGATCGCGACAT-3 The plasmid pGAD426 was generated by insertion of a 1.2 kb Eco RV CYH2 gene fragment, which was isolated from the pAS2-l (Clonetech) into the Pvu II site of pGAD425 (Han and Collicelli, 1995) . 1.2 Construction of yeast strains To allow for the improved yeast two-hybrid system, three Saccharomyces cerevisiae strains L40cc, L40ccu and L40ccuα were created. The S. cerevisiae . L40cc was created by site specific knock-out of the CYH2 and CANl genes of L40 (Hollenberg et al . , Mol. Cell. Biol. 15: 3813-3822), and L40ccu created by site specific knock-out of the URA3 gene of L40cc (Current Protocols in Molecular Biology, Eds. Ausubel et al . John Wiley & Sons: 1992) The strain L40ccuα was created by conducting a mating-type switch of the strain L40ccu by standard procedures (Ray BL, White Cl, Haber JE (1991)). The genotype of the L40cc strain is: Mata his3Δ200 trpl -901 leu2-3 , 112 ade2 LYS2 : : (lexAop) 4 -HIS3 URA3 : : (lexAop) g-lacZ GAL4 canl cyh2, The genotype of the L40ccu strain is: Mata his3Δ200 trpl -901 leu2-3, 112 ade2 LYS2 : : (lexAop) 4 -HIS3 ura3 : : (lexAop) 8 -lacZ GAL4 canl cyh2, and that of L40ccuα is Matα his3Δ200 trpl -901 leu2-3 , 112 ade2 LYS2 : : (lexAop) 4 -HIS3 ura3 : : (lexAop) 8 -lacZ GAL4 canl cyh2. 1 .3 Readout system Figure 5 shows the URA3 readout system carried by the plasmid pLUA. This URA3 readout system under the control of a bacterial LexAop upstream activation sequence (UAS) can be used within the yeast 2-hybrid system both as a counter selective reporter gene and as a positive selection reporter gene to eliminate false positive clones . The plasmid contains the features of the UASι exAop -URA3 readout system, the selectable marker ADE2 that allows yeast ade2-auxotrophs to grow on selective media without adenine and the jla gene which confers amplicillin resistance in E. coli . The plasmid pLUA is a shuttle vector that replicates autonomously in E. coli and yeast. For the construction of pLUA a 1.5 kb Sac I/Cla I UASι exAop - URA3 fragment was isolated from pBS-lexURA and ligated together with a 2.4 kb Sac I/Cla I ADE2 fragment into Cla I digested pGAD425Δ. pBS-lexURA was generated by ligating URA3 fragment together with a UASι exAop fragment into pBluescript SK+ . The URA3 and UASι exAop fragments were obtained by PCR using genomic DNA from S. cerevisiae strain L40c using standard procedures and anchor primers which gave rise to complementary overhangs between the two consecutive fragments which were subsequently anealed to generate the chimeric sequence (see, for example, Current Protocolls in Molecular Biology, Eds. Ausubel et al . John Wiley & Sons: 1992). The ADE2 gene was isolated by PCR using genomic DNA from SEY6210α. pGAD425Δ was generated by deleting of an 1.2 kb Sph I fragment from pGAD425 (Han and Colicelli, 1995) and religation of the vector. 1.4 Generation of a defined interaction library To determine if the invention could be used in an improved two-hybrid system for yeast, as shown in Figure 6 or Figure 7, a defined interaction library of plamids that express various LexA and GAL4ad fusion proteins of interest was constructed using the vectors and strains described in sections 1.1 and 1.2. The orientation of the inserted fragments was determined by restriction analysis and the reading frame was checked by sequencing. The generated constructs and the original plasmids described above are listed in Table 2. The construction of pBTM117c-HDl.6, -HD3.6 and -SIM1 was described elsewhere (Wanker et al . , 1997; Probst et al . , 1997). pBTM117c-HIPl and pGAD427-HIPl were obtained by ligation of a 1.2 kb Sal I HIPl fragment isolated from pGAD-HIPl (Wanker et al . , 1997) into pBTM117c and pGAD427, respectively. pBTM117c-MJD was created by inserting a 1.1 kb Sal I/Not I MJD1 fragment (Kawagushi et al . , 1994) into pBTM117c, and pGAD427-14-3-3 was generated by inserting a 1.0 kb EcoRI/NotI fragment of pGAD10-14-3-3 into pGAD427. For the construction of pGAD427-HIPCT, a 0.5 kb Eco RI HIPl fragment isolated from pGAD-HIPCT (Wanker et al . , 1997) was ligated into pGAD427. pGAD427-lexA and pGAD427-ARNT were generated by insertion of a 1.2 kb Sal I/Not digested lexA PCR fragment and a 1.4 kb Sal I/Not I ARNT fragment into pGAD427 respectively. It was shown that the fusion proteins LexA-SIMl and GAL4ad- ARNT specifically interact with each other in the yeast two- hybrid system (Probst et al . , 1997), because when both hybrids were coexpressed in Saccharomyces cerevisiae containing two integrated reporter constructs, the yeast HJS3 gene and the bacterial lacZ gene, which both contained IΛ β i If) β t vo r- O SH o MH -H β Q φ r- Ol 5 O Φ ti β -H O Φ rt -H CO Φ - A © • tf + 4-1 MH X! 1 XJ φ T ) 0 4-1 O ti c φ Φ β XJ 03 4-1 g ≥ 00 3 β 4-1 β . 4-1 H 4-1 β υ 03 fd Φ 4-1 03 β 4-1 β 0 4 Φ β -H o j σv α. Φ φ Ti φ ,—, O cu MH cd Φ & Φ β Φ TJ Φ to H H Φ O O -H β -H Φ Φ ti u CD A XJ φ Oi H 1 in X! 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CD o O O ti aS SH ti H A φ Φ MH J cu ft & 4-1 ft 4-1 4-1 as 4-1 Oi fe 4-1 a ■ H ■ -H o υ 4-1 O 4-1 ti as 03 4-1 a ϋ 03 a Cn & 4-> a a 4-1 X! β O 4-1 respectively, the resulting cells are no longer able to activate the lacZ reporter gene and do not turn blue after incubation in X-Gal solution. With the membranes from the SD- leu+CAN plate false positive clones expressing an auto- activating GAL4ad-LexA fusion protein were also detected by the β-galactosidase assay. Example 3 : Generation of regular grid patterns of host cells expressing potentially interacting fusion proteins 3.1 Generation of a regular grid pattern of clones from an interaction library in microtiter plates using automation To generate the well defined interaction library, the constructs for the expression of the fusion proteins shown in Figure 8 were pooled and 3 μg of the mixture was co- transformed into yeast strain L40cc by the method of Schiestel & Gietz (1989) . The yeast cells co-transformed with the constructs described in Table 2 were plated onto large 24 x 24 cm agar trays (Genetix, UK) containing minimal medium lacking tryptophan leucine and histidine (SD-leu-trp-his) . The agar trays were poured using an agar-autoclave and pump (Integra, Switzerland) to minimise tray-to-tray variation in agar colour and depth. To maximise the efficiency of automated picking, the transformation mixture were plated such that between 200 and 2000 colonies per agar tray were obtained after incubation at 30°C for 4 to 7 days. Suitable changes to the hardware and software of a standard picking robot designed for the picking of E. coli cells as described by Lehrach et al . (1997) were made to account for the specific requirements of yeast cells. The illumination of agar-trays containing plated colonies was changed from the dark-field sub-illumination to dark-field top-illumination to differentiate yeast colonies from the lawn of non-transformed cells. The existing vision guided motion system (Krishnaswamy & Agapakis 1997) was modified to allow for a larger range of "blob 1 size when selecting yeast colonies to pick from the blob-feature-table returned by connectivity algorithms when applied to a digital image of the agar tray containing colonies. The clone inoculation routine was re-programmed to ensure that cell material which had dried on the picking pins during the picking routine was initially re-hydrated by 10 seconds of immersion in the wells of a microtiter plate before vigorous pin-motion within the well. This robotic procedure ensured that sufficient cell material was inoculated from each picking pin into an individual well of a microtiter plate. The picking pins were sterilised after inoculation to allow the picking cycle to be repeated by programming the robot to brush the picking pins in a 0.3% (v/v) solution of hydrogen peroxide, followed by a 70% ethanol rinse from a second wash-bath and finally drying by use of a heat-gun to evaporate any remaining ethanol from the pins. Furthermore, an algorithm to automatically correct for height variation in the agar was incorporated by referencing the surface height of the agar in three corners and from these points automatically estimating the surface plane of the agar. The robot was further programmed to automatically adjust both the imaging and picking heights according to the agar surface height such that when a pin was extended into a colony, it removed cells only from the top surface of the colony and did not penetrate the whole colony into the growth medium. Finally[B3], we incorporated additional selection criteria that would reliably sort between blue and white colonies . Although the robot provided a method to select only those "blobs' (colonies) within a range of average grey scales (eg, > 80 for white colonies) , this proved unreliable since the actual value of average grey scale required to make a correct discrimination varied across the agar-tray due to slight variation in intensity of the illumination. Therefore, a new method was implemented that automatically modified this discrimination value based on the average illumination of a region of the agar-tray as measured by the camera on a frame- to-frame basis. Often, a "blue' colony that activated the readout system was not uniformly blue across the its whole area, but only the centre would be blue and the surrounding arrangement. Therefore, for each 384-well microtiter plate a regular grid pattern at a density greater that 4 clones per square centimetre was automatically created. 3.2 Creation of regular grid patters of increased density To generate arrays with higher densities, a computer- controlled 96-well pipetting system (Opal-Jena) with automatic plate-stacking, tip washing, liquid waste and accurate x-y positioning of the microtiter plate currently accessed by the tips was employed. The yeast two hybrid cells that had settled in the bottom of the wells of the arrayed interaction library as described above were re-suspended, and a stack of these 384-well plates were placed into the input stacker of the pipetting system. The system was programmed to take a single 384-well microtiter plate containing the arrayed yeast two-hybrid clones and parallel aspirate 10 μl of culture medium and cells into each of the 96 pipette tips from 96 wells of the 384-well plate. The inter-tip spacing of the 96 tips was 9mm and the wells of the 384-well microtiter plate were 4.5 mm so that cells were removed from only every other well along each dimension of the 384-well plate. 8 μl of the 96 aspirated samples contained in the tips were then pipetted in parallel into one set of wells of a sterile 1536- well microtiter plate (Greiner, Germany) . Since the inter- well spacing of this 1536-well microtiter plate is 2.25 mm, yeast cells were deposited into only 1 every 4 wells along each dimension of the 1536-well plate. The remaining 2 μl of culture medium and cells was aspirated to waste before sterilising each 96 tips in parallel. Sterilisation was conducted by twice aspirating and washing to waste 50 μl of 0.3% (v/v) hydrogen peroxide stored in a first replenishable wash-bath on the system, and then aspirating and washing to waste 50 μl sterile distilled water stored in a second replenishable wash-bath. This plate-to-plate pipetting cycle was repeated 3 further times, each time aspirating a different set of 96-clones from Φ X! T) 4-1 φ β TJ φ β rt g β β β β φ * . 4-1 H 4-1 H as rt a β TJ Oi -H β -H -H 4-1 TJ 4-1 β O H a 10 • Φ φ 4-1 4-1 rt as H υ a -H H a Φ β 4-> Tt -H 4-1 τi o Φ β β υ -H -H MH g Φ TJ Φ 1 J Φ 4-1 β a MH 0 as Φ MH Tl 0 o u φ β to as β A membrane sheets sized 222 x 80 mm (Hybond N+, Amersham UK) were pre-soaked in SD-leu-trp-his medium, carefully laid on a sheet of 3mm filter paper (Whatmann) pre-soaked in the same medium and placed in the bed of the robot. The interaction library was automatically arrayed as replica copies onto the membranes using a 384-pin spotting tool affixed to the robot. Five different microtiter plates from the first copy of the interaction library were replica spotted in a "3x3 duplicate 1 pattern around a central ink guide-spot onto 10 nylon membranes - corresponding to approximately 1900 clones spotted at a density of approximately 40 spots per cm . On each replica membrane three different control clones were spotted, each from a microtiter plate that contained the same control clone in every well. One control clone expressed the fusion proteins LexA-SIMl & GAL4ad-ARNT, a second control clone the fusion protein LexA-HIPl, while a third expressed fusion protein GAL4ad-LexA, and all were spotted in order to test the selection, counterselection and the β-gal assay features of the method. To ensure the number of yeast cells on each spot was sufficient for those membranes which were to be placed on the counterselection media plates, the robot was programmed to spot onto each spot position 5 times from a slightly different position within the wells of the microtiter plates. The robot created a data-file in which the spotting pattern produced and the barcode that had been automatically read from each microtiter plate was recorded. Each membrane was carefully laid onto approximately 300 ml of solid agar media in 24 x 24 cm agar-trays. Six membranes were transferred to SD-leu-trp-his media and two each of the remaining membranes were transferred to either SD-trp+CHX or SD-leu+CAN media. The yeast colonies were allowed to grow on the surface of the membrane by incubation at 30 °C for 3 days. 3.4 Generation of a regular grid pattern of clones from an interaction library on non-porous carriers using automation Φ Φ β J 4-1 Φ J 4-1 β o J φ υ as H ft β Φ φ ! 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Similarly, the sequence of the insert encoding for the activation-domain fusion protein following pGADllδ-specific PCR was determined. Sequence comparison of these insets against published DNA sequences using standard sequence comparison tools (e.g. BAST), identified that one interaction involved two previously unidentified gene fragments that were expressed by the positive-clone located in plate 5, well K20. From the predicted protein sequence these two genes were designated Protein A and Protein B. 6.6 Identification of individual members of the interaction by nucleic acid hybridisation Regular grid patterns of the nucleic acids encoding the fusion proteins from the interaction library were constructed. The membranes which had been placed on the SD- leu-trp-his medium and had not been used to assay β-gal activity were processed according to the procedure described in Larin & Lehrach (1990) in order to affix the DNA contained within the clones of the interaction library onto the surface of the membrane . The DNA fragment that encoded Protein A isolated as above, was radioactively labelled by the method of Feinberg & Vogelstein (1983) . This labelled probe was hybridised to an array with DNA from the interaction library affixed to it, and the array washed and detected as 5.1. The number and identity of hybridisation-positive clones was determined for each hybridisation using the automated image analysis system described in Lehrach et al . , (1997) . Seven clones from the interaction library were identified as hybridisation-positive for the probe encoding Protein A. 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J 03 A β O T ) ti ti β MH 4-1 H ■ H β as Φ £ H H ■ H 0 O Φ 4-1 -H -H X! β 4-1 Φ 4-1 Φ 4-1 ti as -H O υ Φ 4-1 as 0 H Φ A β rt CO X! XJ to TJ β 4-> as 4-1 -H > Φ as β β U σv 4-1 MH Xi Φ to as o 4-1 XJ CO Cn 4-1 β 0 -H o Oi as -H Tl X! 03 4-1 T) Φ TJ 0 aS MH © If) o as rl rt 4-1 -H β o Φ β Φ Φ ft X! -H ι 4-1 β H O) Φ 4-1 Φ Φ -H O 03 -H H ti O 4-1 4-1 A TJ υ 4-1 φ -H υ • H rl MH Xi 4-1 A 03 -H φ J 4-1 A β & J β β CJ Φ 03 to fd Φ T ) aS g Xi υ 4-> A O 4-1 Φ β υ -H to β Φ cd as tα A O 4-1 X) 4-1 to v id β rt 4-1 -H Φ Φ £ -H r 03 rH 03 -H β rl rt rl 03 φ Φ σv & td rt as Φ to 0 t , TJ β β β φ 4-1 1 MH xi 4-1 p β g EH 03 XJ H β Φ a 03 β φ ■ H ) Φ A U Φ g XJ xi -H -H Φ O 4-1 XJ as rt -H 4-1 as 0 Φ g 1 03 & rt . ^ , Φ β g td t XJ V rl 4-1 β Ω -1 0 as & H rt β i β £ TJ 4-1 TJ rH MH ft O 03 Φ tn aS MH 4 g X! 4-1 -H O ■ ri Ti A φ o X! 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MH 03 O Φ β β o β rl Φ υ 4-1 4-1 Φ rt a -H 4-1 Tf -H • H tn β o Cn a β Φ as 03 H β rl β -H as Cn Φ MH Φ 4-1 β O MH β O as a β MH β O O o ■ H -H 4-1 β 03 υ O β φ -H MH H 4-1 Φ as id 03 Φ 1 ti Oi Φ υ β β -H a τs to Φ 03 U 4-1 Φ • H as β 4 B a Φ o X β 4-1 φ Φ β CD as 03 H Φ H H A Φ • 4-1 o co β •H φ 4-1 o β a β o ■ rl Ul β MH as Ol β -H 03 03 Φ β a X Φ 03 rl H Φ O 4-1 03 as Φ , Tf Φ 4-1 u φ rl Φ Ul 1 A Tf φ 4J υ β β 4J 03 β O υ 1 H β rt H -H g -H 03 Φ β Φ & 03 β -H cd β 4-1 03 β Φ XJ 4J β β MH X -H CO 4J aS A • 4-1 4J β TJ Φ Φ £ £ Ol p rt -H β MH MH β φ O H 4J υ ft O H Φ *. K rl β Φ aS XI Ul ti tt A >, ■ rl CN rl rl • rl H as tf β 4-1 Φ β rt ■ SS J ! 4-1 g Φ TJ CO XJ Φ φ 4J -H β β o g β H 0 id υ β u MH MH Φ o J β Φ O 4J X β β O Φ -H » g ft J -H φ β *, 4-1 Φ H id ft rl -H X as 4J φ O β -H Φ β 4-1 β as as Φ H g MH •H o MH g 4J -H -H β Ti 03 as blue colonies contained the LexA insert from the pGAD427-LexA construct, and no automatically picked colonies carried this insert. The pBTM117c-HIPl plasmid encoded for the LexA-HIPl fusion protein, and the pGAD427-LexA encoded for the GAL4ad- lexA fusion protein were known to auto-activate the readout system without any partner protein. Hence, automatic visual differentiation has preselected against these false positive clones and automatically created a regular grid pattern of yeast clones expressing a single fusion protein unable to activate the readout system. Example 9 : Automated interaction mating to combine genetic elements in yeast cells 9.1 Automated interaction mating on a solid support in regular pattern The yeast strains that did not express auto-activating fusion proteins in section 8.1 were mated using an automated approach. Each of the yeast strains xia, x2a, ylα and y2α was grown in every well of one of four microtiter plates containing SD-trp-ade medium for the Mata strains and SD-leu- ade medium for the Matα strains . Each plate was labelled with a unique barcode and using a spotting robot such as described by Lehrach et al . (1997), the yeast strains xia and x2a were transferred in a defined 2 x 2 duplicate pattern with an inter-spot spacing of 2mm to Hybond-N+ membrane (Amersham) which had been pre-soaked with YPD medium. The spotting robot then automatically transferred the yeast strains ylα and y2α to the same respective spotting positions on each membrane as, and already containing the xia and x2a clones. The robot automatically sterilised the spotting tool, changed the microtiter plate between each set of clones transferred and created a data-file in which the spotting pattern produced and the barcode that had been automatically read from each microtiter plate was recorded. The spotted membranes were transferred to YPD plates and incubated for over night at 30 °C to allow mating and growth to occur. Each membrane was for 2 hours before plating onto large 24 x 24 cm agar trays (Genetix, UK) . The Mata cells containing the pBTM117c fusion library were plated onto minimal medium lacking tryptophan and adenine but containing 0.2% 5-FOA (SD-trp-ade+FOA) , while the Matα cells containing the pGAD427 fusion library were plated onto minimal medium lacking leucine and adenine but containing 0.2% 5-FOA (SD-leu-ade+FOA) . The colonies on the agar-trays were grown by incubation at 30°C for 4 to 7 days. To minimise false positives arising from dormant cells, the colonies on the two agar-trays were replica-plated onto new agar-trays containing the same respective selective media as a given original tray using standard velvet replication. This replication procedure only transfered cells from the top of a growing colony and thus reduced the carry over of dormant cells and hence the number of false positive clones in the yeast two-hybrid system. These replica agar-trays were incubated at 30°C for 4 to 7 days in order for the yeast cells to grow. To conduct the liquid interaction mating, the resulting Mata and Matα colonies were separately collected off both replica trays by washing with 20 ml of liquid minimal medium. These two mixtures of yeast clones were carefully resuspended, pelleted and washed with sterile distilled water before incubation in 100 ml of YPD in order to ensure that the cells in both mixtures were mating competent. The two populations of mating competent cells were combined in 500 ml of YPD liquid media contained within a 10 litre flat bottomed flask and incubated at 30°C with very gentle shaking (< 60 rpm) overnight to allow interaction mating to proceed. The resulting mixture of diploid cells was pelleted by gentle centrifugation at 3000 rpm for 5 min, washed twice with 50 ml of sterile distilled water and finally, 10 ml of the resulting cell suspension was plated onto each of five 24 x 24 cm agar-trays containing 300 ml of minimal medium lacking leucine, trptophan, adenine, histidine and uracil (SD-leu- trp-ade-his-ura) . The agar trays were poured using an agar- Two E. coli strains KS1-0R2HF + and KS1-OR2HF " were created that carry the sacB conterselective marker under the control of the placθ R 2-62 promoter, and also the tetracycline selective gene under the control of a second placO R 2-62 promoter. Both strains have the sacB counterselective reporter gene stabley inserted within the E. coli chromosome by knock-out of the arabinose operon to enable arabinaose controlled inducible promoters to be utilised. The selective Tet. reporter gene is stabley inserted in within the chromosome by knock-out of the lactose operon which also enables a lacy counterselective marker to be utilised. Strain KS1-0R2HF + was created by transformation of the fertility conferring F' plasmid into KS1-OR2HFZ KS1-OR2HF " was created by site-specific knock-out and insertion of the sacB reporter gene construct into the arabinose operon of strain KSl-ORTet by transformation of the plasmid pK03-araOrsacB and subsequent selection for stable insertions using the method of Link et al . (1997) pK03-araOrsacB was prepared by blunt- ended ligation of a 1.4 Kb OrsacB fragment into Stu I digested pK03-ARA to produce an insert of the OrsacB fragments flanked by 2.5 Kb bp and 1.0 Kb of the 3' and 5' ends of the E. coli arabinose operon respectively. pK03-ARA carries the complete arabinose E. coli operon which had been amplified by PCR from E.coli genomic DNA using tailed primers, digested with Sal I and cloned into the Sal I site of pK03 by standard procedures . The OrsacB fragment was created by ligating together PCR fragments of the placO R 2-62 promoter and the sacB gene. The placθ R 2-62 promoter and sacB PCR fragments were amplifed using standard procedures and anchor primers which gave rise to complementary overhangs between the two consecutive fragments which were subsequently annealed to generate the chimeric sequence (see, for example, Current Protocols in Molecular Biology, Eds. Ausubel et al . John Wiley & Sons: 1992) from the plasmids KJ306-31 and pK03. The lac promotor derivative p2acO R 2-62 carried by the plasmid KJ306-31 was prepared by cleaving the plasmid KJ306 with Hinc II and inserting a 31bp linker sequence (Dove et al. 1997) . The strain KSl-ORTet was created by site-specific knock-out E.coli cells containing the F' fertility factor to F " strains lacking the fertility factor. The plasmid pBAD18-αRNAP was constructed by cloning a 0.7 Kb DNA fragment encoding the α amino terminal domain (NTD) (residues 1-248) of the α-subunit of RNA polymerase (α-NTD) into Eco RI digested pBAD18-CS. The 0.7 Kb α-NTD fragment was isolated by PCR from the plasmid pHTflα (Tang et al . , 1994 Genes Dev 8: 3058-3067) . The plasmid pBAD18-CS was obtained by site-specific insertion assisted by PCR cloning of the 400 bp coding region and translational start site of the rpsL allele into pBAD18-Kan (Guzman et al 1995) before the transcriptional termination signal of the kanamycin gene to enable polycistronic transcription of the counterselective and selective markers . The rpsL allele was obtained by PCR amplification of the plasmid pN01523 (Murphy et al . 1995) . The plasmid pBAD30-cI was constructed by cloning a 730 bp DNA fragment encoding the λcl protein into Eco RI digested pBAD30-TCS. The 730 bp fragment encoding the λcl protein was isolated by PCR from the plasmid pACλcI (Dove et al 1997) . The plasmid pBAD30-TCS was obtained by site-specific insertion assisted by PCR cloning of the 1.3 Kb coding region and translational start site of the lacY gene into pBAD30-T before the transcriptional termination signal of the ampicillin gene to enable polycistronic transcription of the counterselective and selective markers. The lacY gene was obtained by PCR amplification of the plasmid pCMlO (Murphy et al . 1995) . The plasmid pBAD30-T was obtained by site specific insertion of a 288 bp oriT sequence obtained by PCR from the F' plasmid between the M13 intergenic region and cat' locus of pBAD30 (Guzman et al 1995) . 10.2 Detection and identification of interacting proteins using a large-scale and automated prokaryotic two-hybrid system Generation of a libraries of E. coli cells expressing fusion proteins The pSportl plasmid extraction containing the amplified cDNA library of Strongylocentrotus purpuratus described in section 6.1 was used. Approximately 1 μg of the library inserts were then isolated from the plasmid DNA by Hind Ill/Sal 1 digestion and size selective (1 - 1.5Kb) agarose gel purification using standard procedures. The two plasmids pBAD18-αRNAP and pBAD30-cI were prepared by digestion with Hind III/ Sal 1. The insert mixture that was isolated as above was split into two equal fractions and 300 ng [DB4]was ligated with 50 ng of each of the two prepared plasmids. Following ligation, the pBADlδ-αRNAP reaction was then transformed into competent KS1-OR2HF " E. coli cells, and the pBAD30-cI was transformed into competent KS1-0R2HF + E. coli cells. Genetic preselection against false positive clones and the automated creation of a regular grid-pattern of E. coli cells expressing a fusion protein The two transformation mixes were plated onto large 24 x 24 cm agar trays (Genetix, UK) containing selective media. The F ~ cells containing the pBAD18-αRNAP fusion library were plated onto LB selective medium supplemented with kanamycin (50 ug/ml) , arabinose (0.2% w/v) and sucrose (5% w/v) . The F + cells containing the pBAD30-cI fusion library were plated LB selective medium supplemented with amplicillin (100 ug/ml) , arabinose (0.2%) and sucrose (5%). The agar trays were poured using an agar-autoclave and pump (Integra, Switzerland) to minimise tray-to-tray variation in agar colour and depth. After plating, the colonies were grown by incubating the trays at 37°C for 18 to 24 hours. The E. coli cells expressed fusion proteins under the control of the arabinose promoter, and those cells expressing single fusion proteins able to auto-activate the sacB reporter gene were unable to grow, β TJ rl rH O φ H O -H β Φ β 03 β S 4J β β β MH 4-1 to o -H ϋ Ol φ β β 03 φ -H φ td xi 03 Oi 4J 03 φ Φ β 4-1 β β φ as Φ ft 4J ti TJ X β 4J β Φ O to β ft A 03 Φ β β rH β 03 -H H Φ Φ Kl H 4J υ υ rt O as CD β Φ rl 1 ft 03 X O φ β XJ A Φ O 4-1 4-1 XJ 4-1 03 Ti Φ β β 4-1 MH MH as rt o > TJ » • H β Φ β 4-1 o 03 Φ U 03 4-1 rt 4-1 Φ O o β g O td ft o 4-1 φ X β β β Φ ft as o 03 φ O -H 4 H CQ 4J 4-1 H O aS t Φ β Φ O H A XI N -H as as β 4 ti Φ O as Ul β O β -H » Φ X) Cq A Φ β 4J 4J Φ & Φ 0 β O X! MH β H β EH 0 ft X! X ! i σv CU • H υ Cu ro , CN H - v o f σv σv - O a β o φ H XJ 03 4J β MH g 0 Ol β β MH H 4J fi U Φ rt X β id Φ 4J 4J β β H Φ Φ β X! O MH TJ as Φ A J o 4J u aS β A φ 4J 4J φ aS β as 4J ti 03 £ Φ H g g 03 Φ id β 0 a -. 0) CQ β β H -H >ι Φ β 4-1 β 0 rt β υ a Treizenberg, S. and Ptashne, . (1988), Nature 335: 559-560) positioned immediately upstream of the coding sequence for the enhanced green fluorescent protein (EGFP; Yang, T.T., Cheng, L. and Kain, S.R. (1996), Nucl. Acids Res. 24 (22): 4592-4593) . These reporter plasmids are generated by replacing the coding sequence for CAT in G5ElbCAT (Dang, C.V., Barrett, J., Villa-Garcia, . , Resar, L.M.S., Kato, G.J. and Fearon, E.R. (1991), Mol. Cell. Biol. 11: 954-962) by the EGFP coding sequence and introducing either a neomycin, hygromycin or puromycin resistance marker gene (neo r , hyg r or pur ) using standard subcloning procedures. The plasmids pMneol,2,3 or pMhygl , 2 , 3 , which are derived from pMl,2,3 (Sadowski, I., Bell, B., Broad, P. and Hollis, M. (1992), Gene 118: 137-141) by insertion of either neo r or hyg r marker gene using standard subcloning procedures, are series (1,2,3 correspond to three possible reading frames) of improved Gal4p- fusion vectors derived from the pSG424 plasmid, which was designed for mammalian expression of fusion proteins that contain the DNA-binding domain of the yeast Gal4 protein (Sadowski, I. and Ptashne, M. (1989), Nucl. Acids Res. 17: 7539). This vector contains a polylinker preceded by coding sequences for Gal4p amino acids 1-147. Thus, a hybrid reading frame that encodes a Gal4p-fusion protein can be generated by inserting cDNA sequences into the polylinker region of pSG424/pM"s. Transcripts of the hybrid reading frame are inititated from the SV40 early promoter and their processing is facilitated by the SV40 polyadenylation signal. Alternatively, the hybrid reading frames are subcloned into pLXSN or any other similar retroviral vector to allow packaging cell line-aided infection of target cells. The plasmids pVP-Nconeo and pVP-Ncohyg are derived from pVP- Nco vector (Tsan, J., Wang, Z., Jin, Y., Hwang, L., Bash, R.O., Baer, R. The Yeast Two-Hybrid System, edn 1. Edited by Bartel, P.L., Fileds, S. New York: Oxford University Press (1997) : 217-232) by insertion of either a neo r or hyg r marker Φ 03 td υ XJ u -H J & 1 O β 4-1 -H β aS - β -H β Φ aS 4-1 O l β as a O β 4-1 o • H τS 03 φ β ti MH ti 1 Φ β MH ■ H Φ rt β g o Φ TJ A Oi TJ β H • H β Tf O β 5 -H X) β 1 -H rt! Φ a 4-1 P O β id a Oi β β 0 -H -H CO 10 03 β Φ MH β 8 X* Φ XJ Φ 4-1 If) β 03 If) Φ β Ul PQ o 0 TJ A o H o Ol 1 r- Ol -H 00 • H 4-1 φ β as • H H 4-1 O H > Φ β H © as β 03 φ 00 Ol > O CO Φ 4J H 00 tu TJ O rt σv Φ H ■ H 03 > • tf < 03 Oi β -H ti g β U τs β rt -H β 0. X! XI O 03 Φ -H *-— * H β -H 4J *. O Φ MH Φ Φ TJ MH β g Φ 4-1 -H rl s rt 4J β 03 β 4-1 • H -H 4J • H rl 4-1 . β 4-1 > Φ CO O XJ O MH O 4 rl 0 Φ ft υ J rl Φ 4J β 03 H ft to Φ Ol Φ υ 0 to 03 Φ Φ 4-1 Φ - \ υ 4-1 03 TJ as -H β X φ β 4-1 υ Φ υ > O O as g u β 4-1 Φ Xi Φ β Φ 00 X! XJ MH O) Cu Φ β CO ft Φ ft O Oi β υ rt 03 ft β β to -H • H β -r-ι as > MH O H 4J β MH β β β MH 4-1 03 β X to ft β a g β φ H -H β ft > 4-1 O X! ■ ri υ • tf O O O -H -H -H O υ -H MH Φ β φ β φ Φ Φ X! H 4-1 rH Φ rt TJ Φ cd ft β τs 4-1 β CD 4J MH N, β Φ Φ > O β H -. 4-1 υ EH as O H 03 g β φ TJ > Φ to φ O β 03 O 03 β β Φ Φ 4J H • r-> O) 03 MH .— .. Φ 10 03 C rt Φ H O 4J -H β X) Φ as 03 03 Φ O o Φ 4J O O X! O β rl φ B > vo ι Φ . Ul O as φ -H rt β 4-1 β •H ft ti β U as 4-1 β -H -H β as β O β 4-1 -H rl Ol J β rt en 03 β φ ■ ri 4-1 MH β 4-1 g O υ ro Φ β 03 A o -H A β Φ 4-1 4-1 O ■ rl ft ft to 4J φ β 4-1 Is cn o υ > o TJ o υ o -H as cn XJ υ Φ -H MH 4-1 rt O) -H O 03 β g cd o -H C^ H 4-1 β • H β Φ MH TJ β 4-1 4J o N 4-1 to β H O 4-1 ft TJ Φ ft β rl β Φ > β MH o >*. β rl > Φ 4-1 O 03 β aS 4-1 φ fi ■ H -H β Tl MH 4-1 0 o as Φ 4J -H g Φ O in β O MH φ ti to CO β aS rl β MH Φ TJ β << O XI 03 Φ <$ 03 β β -H β XJ to 4-1 φ Φ — o • Ti TJ Φ H -H β Φ as A as o β O a -H -H TJ g X β Φ ft 03 O 4-1 *. υ 4-1 β ι 4-1 tf rt as |3 H 03 O xi Tt as as to p 4-1 4-1 Φ P ti • rt β ft β H 03 as 03 CJ 4-1 4-1 aS . Φ β Φ CQ -H 4-1 MH Φ l H as 03 u O fi β o aS Ul β cr id MH U 03 1 03 -H XJ 4-1 CO β Cn o B U rt 4-1 -H o X ti Ul O Ul TJ Φ cd -H MH 1 B ti 4-1 Φ -H 4J 0 to H Ol -H β -H Φ td Φ β Φ Φ O β ft -H Φ H 03 o 03 β β H β 4-1 * -, -H -H υ - Oi -H 4-1 4-1 ti 4-1 β to ■ H Ul ti ft -H Φ g xi Φ Oi Φ 4-1 Φ 4-> TJ X) as -H O 03 O β 4-1 A X) H X β β to υ to A β -H CQ β rl aS ft Φ 4-1 to 4-1 CO β TJ cd XJ O β β rt ft H Ti as β as φ ■ H -H β φ >ι φ Φ g -H as 1 H X rl 4-1 to as -H Xi 4-1 Φ O 01 Oi g H rt o τs 4-1 id β 4-1 Ul 4-1 υ -H Φ β Φ as 0 H Oi . , 03 4J > U en fi o 4-1 Φ Φ Ul TS Φ Φ β φ Ui O Φ φ 0 O H 03 B O as β β fi ft β Φ O -H g Φ φ Ol -H τs β υ β Ul id -H A Φ 4-1 4J TJ ti φ Φ β 4J 4-1 O ft O -H U H β O TJ 03 X! H β as Φ Φ MH 4-1 υ as TJ -H Φ φ g β O *. υ ti cd H -H Cn β β ft fi Φ β Φ 4J -H fi 4J β Φ ti β -H to -H β β TJ 4-1 o o -. 4-1 X! φ O XJ O fi 4J >-ι -H Φ g O X MH 4-1 Φ β o H Φ xi ft 4J β Φ β as O ι φ β β β *. as 4-1 4J o O XJ cd β Φ -H ti U XJ cr -H β 4-1 4-1 X TJ β o β ft 2 A 4-1 O MH o H > 03 Φ 03 H -H Φ o 4-1 cr 4J as 4-1 Φ 4-1 MH Φ 4-1 03 β Φ Φ Φ MH o O • as ft H Φ ■ rl H TJ β 03 o 03 MH o β Φ to υ B β MH -H as Φ O Oi 03 J β β P • Φ B Φ TJ MH > 4J H O H ft β fi ft β 4-1 fd -H H ft , — , β o β Φ • H υ Φ id 4-1 a o 03 H φ Φ β β > β H MH -H 1 υ H H φ β -H o -. MH ■ H Φ -H as A H MH ft .*-, ro O 4-1 4-1 as 4-1 as U id Φ Oi - \ ft Φ Φ υ Φ - \ MH O 4-1 Φ β CO A 1 Φ 4 as Oi cn TJ β ft β td 1 > * . H CJ β Ol > 03 o O 03 β MH TJ β U XJ β 4-1 ft X! β β β tn rt tf o Ol β O MH XI β -H β fi ft φ 4-1 as MH Φ Ol as TJ rt 4-1 Tf fe Φ Φ Φ φ ■ tf β CD 03 β β 4-1 O ft MH β ■ H O > as Ti MH 4-1 ■ H 4-1 fi Ul as to Φ β 03 o β β Φ A XJ 1 Φ β ■ H Φ β β ■ H 0 -H TJ -H β -H > Φ H 03 TJ O • H Ul Φ β - 4-1 Φ H pq id cr β 4-1 J CN XJ as Φ TJ 03 4-1 as Ol 0 β rt β 4-1 O 4-1 ■ ri 4-1 -H Φ 4-1 Φ 4-1 as 03 υ Φ H υ Φ Ol cn 4-1 X! β β rl β rt β g -H υ cd 4-1 O . 03 03 MH O υ to ti β φ β Φ Φ 03 XJ -. in -H * . 4-1 as <$ Cn -H β g O φ A φ O > o Φ Φ Φ -H 03 Φ Φ β 4-1 XJ MH u υ XJ to β as 4J • ■ tf Φ X! g β rl o 0 -H β 1 MH Φ -H as MH β β β H β -H EH β CQ 4-1 β o -H EH J τs Φ • -H H i-> β 4-1 03 fi β Ul β Φ g as Φ ^ — . -H Φ o υ 4J |3 • •• 03 β Φ φ 4J .— - 03 •H as υ aS Φ a β O Φ β -H XJ Φ Φ ti to Φ -. Oi • ---- β 4J β 4-1 -H EH ^ -, -H O 4-1 4-1 03 CO 03 X H -H β XJ p rt TJ as xi 4-1 4-1 X) ^ -, β TJ Tl o rt H td TJ g β Ol id as J Φ β g • H 4-1 β a ti TJ H 4-1 03 03 σv = -H Φ φ -H -H > β φ 0 - Ol β Φ > -H 03 β H ft g Oi 4-1 1 H 4J Φ rt ι *. U o If) ti 4J CO 4-1 4-1 4J • • H as -H Ol — ' O ft •H 4J fe ft td -H Cn -H » β ft cd 4-1 β 4J 03 H -H as 0 U 03 u υ β 03 4-1 o 4-1 β ■ H O 4-1 β β — X > β β H to -H TJ > β vo U O rt CQ 4-1 B JO 4-1 rt Φ φ φ Φ β o ft 4-1 rt as • tf 4J υ O Φ Φ φ o rt -H Φ β to β ft -H H Φ ■ H XJ 4-1 β O σv rt β β MH H β -H as fe H H CN rt 03 id β 4-1 φ g g , -H 03 O > ft MH 4-1 4-1 β v O • H σ ti > φ ft 03 φ Φ Φ I CD 03 β > o Φ ti υ 03 Φ o 0 β Φ Φ υ Cn o > 03 ft O -H X! o O -H 4J X β 03 MH 4-1 0 pq H g • ■ H β 4J MH 0 > H β β H Φ 4-1 β φ β ti β O Φ TJ > •H 4J 4J β φ as Φ MH O 4-1 H ■ H . — . 03 4-1 o as MH ft • H H o ft 4J O ft tα -H 4-1 Φ cd β as Φ 4-1 υ U -H o ti β -H β β MH Φ 4-1 g Φ U -H A •H φ Φ Φ , -H g MH β X 03 Φ Xi β 03 β Φ β β Φ as "— ' u 4J ft J ft rt O V 03 β tf rt g A TJ β TJ υ X! g Φ ft Φ as β β 4-1 4-1 -H 03 ti ft as > domain-cDNA fusion library) plasmids. Although the number of false positives from pVP-Nco plasmids is usually much lower than from pMl,2,3 (DNA binding domain-cDNA fusion library) plasmids , it may under some circumstances be necessary to apply a double preselection strategy. To that end two different polyclonal pools of stable cell lines expressing either members of the p - or pVP-Nco-cDNA fusion library are generated by transfection/infection of the 293 reporter cell line and selected by means of the respective (different) antibiotics (G418 and HygB) as described above. Both pools of cell lines are then subjected separately to preselection and elimination of false positive clones as detailed above. In order to combine both fusion vectors and their corresponding expressed fusion proteins in one cell, individual cells of both pools of cell lines are fused together using state-of-the-art cell fusion-protocols involving PEG-facilitated electrofusion as described in Li, L.-H. and Hui, S.W. (1994), Biophys . J. 67: 2361-2366; Hui, S. ., Stoicheva, N. and Zhao, Y.-L. (1996), Biophys. J. 71: 1123-1130, and Stoicheva, N. and Hui, S.W. (1994), Membrane Biol. 140: 177-182. Fusions between one cell of both pools is desired. For that purpose one cell of each pool is placed into each well of a multiwell dish as detailed above. After cell fusion, the combined cells are then subjected to visual selection. Cells are left on the same dish for visual or automated screening or collected and sorted by FACS . 11.6 Double Preselection and Cell Fusion Using an Inducible Expression System A disadvantage of the above described double preselection method is that proteins with toxic or anti-proliferative effects and their corresponding cDNAs will be lost during the lengthy selection process necessary to establish polyclonal pools of stable cell lines for both cDNA-fusion library- such as PT67, followed by a hyg gene (selectable marker) and seven copies of tetO fused to the cytomegalovirus (CMV) minimal promoter immediately 5 'of the polylinker. Ψ+ and polylinker sequences are flanked by 5'and 3'LTRs, respectively. pREV-TRE is available from Clonetech Inc.. cDNA libraries are subcloned into the polylinker of pREV-TRE. The above described reporter cell lines are separately infected with either pREV-TRE-Gal4- or pREV-TRE-VP16-derived retroviral particles. A polyclonal pool of new stable cell lines is selected in both cases using the resistance selection marker gene hyg . Transient expression of fusion proteins from pREV-TRE plasmids has to be induced by withdrawal (Tet-Off) or addition (Tet-On) of Tet in order to allow for double preselection and elimination of false positives as described above. 11.7 Cell Fusion and Selection for Cells Expressing Interacting Proteins The remaining polyclonal pools of cell lines are then subjected to cell fusion as described above. The HygB concentration in the culture medium is increased to minimize a possible loss of either one component of the pairs of fusion protein cDNA sequences present in all fused cells. For the detection of positive clones, i.e. cells expressing a pair of interacting proteins (as detailed above) , expression of fusion proteins has to be induced by addition or withdrawal of Tet . References : Allen, T.B., alberg, M. . , Edwards, M.C., Elledge, S.J. 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Oligonucleotide Sequence (5' -3') a sense TCGAGTCGACGCGGCCGCTAA A antisense GGCCTTAGCGGCCGCGTCGAC b sense TCGAGGTCGACGCGGCCGCAGTAA B antisense GGCCTTACTGCGGCCGCGTCGACC c sense TCGAGAGTCGACGCGGCCGCTTAA c antisense GGCCTTAAGCGGCCGCGTCGACTC Table 2 Two-hybrid vectors used for the expression of fusion proteins . Plasmid Fusion- Insert Counter- SelecFusion protein (kb) selection tion protein in yeast Reference PBTM117C LexA - CANl TRPl N/A pBTM117c-HDl .6 LexA-HD1.6 1.6 CANl TRPl Wanker et al., 1997 pBTM117c-HD3.6 LexA-HD3.6 3.6 CANl TRPl Wanker et al., 1997 pBTM117c-SIMl LexA-SIMl 1.1 CANl TRPl Probst et al., 1997 pBTM117c-MJD LexA-MJD 1. .1 CANl TRPl this work pBT 117c-HIPl LexA-HIPl 1. .2 CANl TRPl this work PGAD427 GAL4ad - CYH2 LEU2 N/A pGAD427-ARNT GAL4ad- 1. .4 CYH2 LEU2 Probst et ARNT al., 1997 pGAD427-HIPl GAL4ad- 1. .2 CYH2 LEU2 Wanker et HIP1 al., 1997 pGAD427-HIPCT GAL4ad- 0. .5 CYH2 LEU2 Wanker et HIPCT al., 1997 pGAD427-14-3-3 GAL4ad-14- 1. .0 CYH2 LEU2 this work 3-3 pGAD427-LexA Gal4ad- 1 .2 CYH2 LEU2 this work LexA Table 3 Yeast strains used for the 5-FOA counterselection and the automated interaction mating Strain Plasmids Selected on xia pBTM117c / pLUA SD-trp-ade x2a pBTM117c-SIMl / pLUA SD-trp-ade x3a pBTM117c-HIPl / pLUA SD-trp-ade ylα pGAD427 / pLUA SD-leu-ade y2α pGAD427-ARNT / pLUA SD-leu-ade y3α pGAD427-LexA / pLUA SD-leu-ade Table 4 Identification of fusion proteins that activate the URA3 readout system, a . Strain Plasmids SD-trp SD-trp SD-trp -ade -ade+5- -ade- FOA ura xia pBTM117c / + + - pLUA x2a pBTM117c-SIMl + + / pLUA x3a pBTM117c-HIPl + + / pLUA SD-trp-ade: Selective medium lacking tryptophan and adenine. SD-trp-ade+5-FOA: Selective medium containing 0.2 % 5-FOA. SD-trp-ade-ura: Selective medium lacking tryptophan, adenine and uracil. Strain Plasmids SD-leu SD-leu SD-leu -ade -ade+5-FOA -ade-ura ylα pGAD427 / pLUA + + y2α pGAD427 + + -ARNT/pLUA y3α pGAD427 + -LexA/pLUA SD-leu-ade: Selective medium lacking leucin and adenine. SD-leu-ade+5-FOA: Selective medium containing 0.2 % 5-FOA. SD-leu-ade-ura: Selective medium lacking leucin, adenine and uracil . Table 5 Identification of fusion proteins that activate the LacZ readout system. A. L40ccu yeast cells transformed with pBTM117c plasmid constructs expressing a fusion protein comprising the LexA DNA binding domain are plated on minimal medium lacking trptophan, buffered to pH 7.0 with potassium phosphate and containing 2 ug/ml of X-Gal (SD-trp/XGAL) : Results for the state of the readout system for various auto-activating and non-auto-activating fusion proteins Plasmid Fusion Growth on Blue Construct protein SD-trp/XGAL colouration pBTM117c LexA + pBTM117c-HD1.6 LexA- -HD1.6 + pBTM117c-HD3.6 LexA- -HD3.6 + pBTM117c-SIMl LexA- -SIM1 + pBTM117c-MJD LexA- -MJD + pBTM117c-HIPl LexA- -HIPl + B. L40ccuα yeast cells transformed with pGAD427 plasmid constructs expressing a fusion protein comprising the GAL4ad activation domain are plated on minimal medium lacking leucine, buffered to pH 7.0 with potassium phosphate and containing 2 ug/ml of X-Gal (SD-leu/XGAL) : Results for the state of the readout system for various auto-activating and non-auto-activating fusion proteins. Plasmid Fusion Growth on Blue Construct protein SD- -leu/XGAL colouration pGAD427 GAL4ad + - PGAD427-ARNT GAL4ad-ARNT + - PGAD427-HIPI GAL4ad-HIPl + - PGAD427-HIPCT GAL4ad-HIPCT + - PGAD427-14-3-3 GAL4ad-14-3-3 + - PGAD427-LexA Gal4ad-LexA + +

Claims: C L A I S 1. A method for the identification of at least one member of a pair or complex of interacting molecules from a pool of potentially interacting molecules, comprising: (A) providing host cells containing at least two genetic elements with different selectable markers, said genetic elements each comprising genetic information specifying one of said potentially interacting molecules, said host cells further carrying a readout system that is activated upon the interaction of said molecules; and (B) allowing at least one interaction, if any, to occur; (C) selecting for said interaction by transferring host cells or progeny of host cells to a selective medium that allows identification of said host cells upon activation of the readout system; and (D) identifying host cells that contain molecules that activate said readout system upon said selective medium; (E) identifying at least one member of said pair or complex of interacting molecules; wherein at least one of the steps (A) , (C) or (D) is effected or assisted by automation creating or analysing a regular grid pattern of host cells. 2. The method of claim 1, wherein said pair or complex of interacting molecules is selected from the group consisting of RNA-RNA, RNA-DNA, RNA-protein, DNA-DNA, DNA-protein, protein-protein, protein-peptide or peptide-peptide interactions. 3. The method of claims 1 or 2, wherein said genetic elements are plasmids, artificial chromosomes, viruses or other extrachromosomal elements . 4. The method of claims 1 to 3, wherein said interactions lead to the formation of a transcriptional activator comprising a DNA-binding and a transactivating protein domain and which is capable of activating a response moiety driving the activation of said readout system. 5. The method of claims 1 to 4, wherein said readout system comprises at least one detectable protein. 6. The method of claim 5, wherein said detectable protein is encoded from at least one of the genes lacZ, HIS3, URA3, LYS2, sacB, tetA, gfp, yfp, bfp, cat, luxAB, HPRT or a surface marker. 7. The method of claims 1 to 6, wherein said readout system comprises at least one counterselectable gene. 8. The method of claim 7, wherein said counterselectable gene is one of URA3 , LYS2, sacB, CANl, CYH2 , rpsL or lacY. 9. The method of claim 7 or 8, wherein, prior to step (A), a preselection against clones expressing a single molecule able to activate the readout system is carried out in or on culture media comprising a counterselective compound. 10. The method of claim 9, wherein said counterselective compound is 5-fluoro orotic acid, canavanine, cycloheximide, a-amino adipate, sucrose, streptomycin or 2-nitrophenyl-β-D-thiogalactosidase. 11. The method of claims 1 to 6, wherein said readout system comprises at least one detectable protein that allows host cells upon activation of said readout system to be visually differentiated from host cells in which said readout system has not been activated. 12. The method of claim 11, wherein said detectable protein is encoded by at least one of the genes lacZ, gfp, yfp, bfp, cat, luxAB, HPRT or a surface marker gene. 13. The method of claims 11 or 12, wherein, prior to step (A) , a preselection against host cells expressing a single molecule able to activate the readout system comprising said detectable protein is performed. 14. The method of claim 13, wherein the optionally automated identification of clones expressing a single molecule unable to activate the readout system is effected by visual means from consideration of the activation state of the readout system. 15. The method of claims 1 to 14, wherein said host cells are yeast cells, bacterial cells, mammalian cells, insect cells, plant cells or hybrid cells. 16. The method of claims 1 to 15 further comprising transforming, infecting or transfecting at least one set of host cells of said sets of host cells with said genetic element or genetic elements prior to step (A) . 17. The method of claims 1 to 16 further comprising transforming, infecting or transfecting one set of host cells of said sets of host cells with at least one genetic element prior to step (A) , selecting against host cells in said one set of host cells expressing a molecule able to auto-activate said readout system and transforming, infecting or transfecting said set of host cells with at least one further genetic element prior to step (A) . 18. The method of claims 1 to 17, wherein cell fusion, conjugation or interaction mating is used for the generation of said host cells with said genetic elements prior to step (A) . 19. The method of claim 18, wherein said cell fusion, conjugation or interaction mating is effected or assisted by automation. 20. The method of claim 19, wherein said automation is effected by an automated picking, spotting, rearraying, pipetting, micropipetting or cell sorting device. 21. The method of claim 20, wherein said device is a picking robot, spotting robot, rearraying robot, pipetting system, micropipetting system or fluorescent assisted cell sorting (FACS) system. 22. The method of claims 1 to 21, wherein said selectable marker is an auxotrophic or antibiotic marker. 23. The method of claim 22, wherein said auxotrophic or antibiotic marker is LEU2, TRPl, URA3 , ADE2 , HIS3, LYS2 , kan, bla, Zeocin, rpsL, neomycin, hygromycin, pyromycin or G418. 24. The method of claims 1 to 23, wherein host cells or progeny of host cells of step (B) are transferred to a storage compartment. 25. The method of claim 24, wherein said transfer to a storage compartment is effected or assisted by automation. 26. The method of claim 25, wherein said automation is effected by an automated arraying, picking, spotting, pipetting, micropipetting or cell sorting device. 27. The method of claim 26, wherein said automation is implemented by the use of a picking robot, spotting robot, automated pipetting or micropipetting system or fluorescent assisted cell sorting (FACS) system. 28. The method of claims 25 to 27, wherein said storage compartment comprises an anti-freeze agent. 29. The method of claims 25 to 28, wherein said storage compartment is at least one microtiter plate. 30. The method of claim 29, wherein said microtiter plate comprises 96, 384, 846 or 1536 wells. 31. The method of claims 1 to 30, wherein said transfer in regular grid pattern optionally effected by automation in step (C) is effected by an automated picking, spotting, replicating, pipetting, micropipetting or cell sorting device. 32. The method of claim 31, wherein said device is a picking robot, spotting robot, replicating robot, pipetting system, micropipetting system or fluorescent assisted cell sorting (FACS) system. 33. The method of claims 31 to 32, wherein said transfer is made by multiple transfers carrying additional host cells to the same position in said regular grid pattern. 34. The method of claims 31 to 33, wherein said transfer is made to at least one carrier. 35. The method of claim 34, wherein said at least one carrier is a microtiter plate and the regular grid pattern is at densities greater than 1, preferably greater than 4, more preferably greater than 10, most preferably greater than 18 clones per centimeter square. 36. The method of claim 34, wherein said at least one carrier is a porous support and the regular grid pattern is at densities in the range of 1 to 10, preferably 10 to 50, more preferably 50 to 100, most preferably greater than 100 clones per centimeter square. 37. The method of claim 34, wherein said at least one carrier is a non-porous support and the regular grid pattern is at densities in the range of 1 to 100, preferably 100 to 500, more preferably 500 to 1000, most preferably greater than 1000 clones per centimeter square . 38. The method of claims 1 to 37, wherein the identification of host cells in step (D) from consideration of the activation state of said readout system is effected by automation using visual means . 39. The method of claims 1 to 38, wherein the identification of host cells in step (D) from consideration of the activation state of said readout system is effected by digital image capture, storage, processing, and/or analysis . 40. The method of claims 1 to 39, wherein the identification of said at least one member of said pair or complex of interacting molecules in step (E) is effected by nucleic acid hybridisation, oligonucleotide hybridisation, nucleic acid or protein sequencing, restriction digestion, spectrometry or antibody reactions. 41. The method of claims 1 to 40, wherein the identification of said at least one member of said pair or complex of interacting molecules in step (E) is effected using a regular grid patterns of said at least one member or of said genetic information encoding said at least one member . 42. The method of claim 41, wherein construction of regular grid patterns in step (E) is effected or assisted by automation. 43. The method of claims 1 to 41, wherein said automation in step (E) is effected by an automated spotting, pipetting or micropipetting or cell sorting device. 44. The method of claim 43, wherein said automation in step (E) is implemented by employing a spotting robot, spotting device, pipetting system or micropipetting system. 45. The method of claims 41 to 44, wherein said identification is effected by digital image capture, storage, processing and/or analysis. 46. The method of claims 1 to 45, wherein nucleic acid molecules, prior to said identification in step (E) , are amplified by PCR or are amplified in a different host cell as a part of said genetic elements, preferably in bacteria and most preferably in E. coli. 47. The method of claims 1 to 46, further comprising: (F) providing at least one of said genetic elements in step (A) , which additionally comprises or comprise a counterselectable marker, wherein said counterselectable markers are different for each type of genetic element; (G) selecting for interaction by transferring host cells or progeny of host cells which transfer is optionally effected or assisted by automation in a regular grid pattern, in step (C) to (i) at least one selective medium that allows growth of host cells only in the absence of a counterselectable marker specified in (F) and in the presence of a selectable marker; and (ii) a further selective medium that allows identification of host cells upon activation of the readout system; (H) identifying host cells in step (D) that contain interacting molecules that: (iii) do not activate said readout system on said at least one selective medium specified in (i) , and (iv) activate said readout system on said selective medium specified in (ii) . 48. The method of claim 47, wherein the genetic element that additionally comprises a counterselectable marker further specifies an activation domain fusion protein. 49. The method of claims 1 to 46, further comprising: (I) providing at least two of said genetic elements in step (A) , which additionally comprise different counterselectable markers; (J) selecting for interaction by transferring host cells or progeny of host cells, which transfer is optionally effected or assisted by automation in a regular grid pattern, in step (C) to (v) at least one selective medium, wherein said selective medium allows growth of said host cells only in the absence of the first counterselectable marker of said counterselectable markers as specified in (I) and in the presence of a first selectable marker; (vi) at least one selective medium, wherein said selective medium allows growth of said host cells only in the absence of the second counterselectable marker of said counterselectable markers as specified in (I) and in the presence of a second selectable marker; (vii) a further selective medium that allows identification of said host cells upon activation of the readout system; and (K) identifying host cells that contain interacting molecules that: (viii) do not activate said readout system on said at least one selective medium specified in (v) ; and (ix) do not activate said readout system on said at least one selective medium specified in (vi) ; and (x) activate said readout system on said selective medium specified in (vii) . 50. The method of claim 49, wherein said at least two genetic elements that additionally comprise a counterselectable marker further specify a DNA binding domain fusion protein and an activation domain fusion protein, respectively. 51. The method of claims 47 to 50, wherein said counterselectable marker or counterselectable markers of step (F) or (I) are selected from the group of URA3, LYS2, sacB, CANl, CYH2 , rpsL, lacY, D mu or cytosine deaminase . 52. An array of clones on a carrier produced by automation at a density greater than 5, wherein each clone comprises: (L) a readout system or part of a readout system,- and (M) one genetic element or a combination of more than one genetic elements, said genetic element or elements each comprising a selectable marker and genetic information comprising one part of a multipart functional entitiy fused to one potentially interacting molecule. 53. An array of clones not derived from yeast or bacterial cells on a carrier, wherein each clone comprises: (N) a readout system or part of a readout system; and (0) one genetic element or a combination of more than one genetic elements, said genetic element or elements each comprising a selectable marker and genetic information comprising one part of a multipart functional entitiy fused to one potentially interacting molecule. 54. The array of clones of claims 52 or 53, wherein said genetic element or combination of genetic elements is identical in not more than 10 %, preferably not more than 5 %, more preferably not more than 2 %, most preferably not more than 1 % of clones in the array. 55. The array of claims 52 to 54, wherein said genetic element or at least one of said combination of genetic elements further comprises a counterselectable marker. 56. The array of claims 52 to 55, wherein said one part of a multipart functional entity is a transactivating or DNA binding domain. 57. The array of claims 52 to 56, wherein the array is produced by a picking robot, spotting robot, pipetting system, micropipetting system or fluorescence assisted cell sorting (FACS) system. 58. The array of claims 52 to 57, wherein the carrier is at least one microtiter plate, a porous or. non-porous support . 59. The array of claim 58, wherein the at least one microtiter plate contains 96, 384, 846 or 1536 wells. 60. The array of claim 52, wherein the number of different clones is greater than 10000. 61. The array of claim 53, wherein the clones are mammalian cells or insect cells or plant cells. 62. An array of clones on a carrier, wherein each clone comprises : (P) a readout system; and (Q) at least two genetic elements each encoding one part of a multipart functional entitiy fused to one interacting molecule, wherein the interaction between the at least two interacting molecules reconstitutes the multipart functional entity, which in turn is able to activate the readout system. 63. A method for the production of a pharmaceutical composition comprising formulation of said at least one member of said pair or complex of interacting molecules identified by the methods of claims 1 to 51 in a pharmaceutically acceptable form. 64. A method for the production of a pharmaceutical composition comprising formulating an inhibitor of the interaction the at least one member of said pair or complex of interacting molecules identified by the methods of claims 1 to 51 with another molecule, preferably also identified by the methods of claims 1 to 51, in a pharmaceutically acceptable form. 65. A method for the production of a pharmaceutical composition comprising identifying a further molecule of a cascade of interacting molecules of which at least one of said interacting molecules identified by the methods of claims 1 to 51 is a part of or identifying an inhibitor of the function of said further molecule. 66. Kit comprising at least one of the following: (R) A carrier comprising an array of clones as identified in claims 52 to 62; and/or (S) a device allowing access to information on the computer readable memory characterising the clones in or on said carrier. 67. Use of the kit of claim 66 to identify interactions that are inhibited by a substance under investigation. 68. A method for the identification of at least one member of a pair or complex of interacting molecules, comprising: (T) providing host cells containing at least two genetic elements with different selectable markers, said genetic elements each comprising genetic information specifying one of said members, sat least one of said genetic elements that further specifies an activation domain fusion protein additionally comprising a counterselectable marker, said host cells further carrying a readout system that is activated upon the interaction of said molecules; (U) allowing at least one interaction, if any, to occur; (V) selecting for said interaction by transferring progeny of said host cells in a regular grid pattern effected by automation to: (xi) at least one selective medium, wherein said selective medium allows growth of said host cells only in the absence of said counterselectable marker and in the presence of a selectable marker; and/or (xii) a further selective medium that allows identification of said host cells only on the activation of the readout system,- (W) identifying host cells that contain molecules that: (xiii) do not activate said readout system on said at least one selective medium specified in (xi) ,- and (xiv) activate said readout system on said selective medium specified in (xii) ; and (X) identifying at least one member of said pair or complex of interacting molecules. 69. A computer implemented method for, storing and analysing data relating to potential members of at least one pair or complex of interacting molecules encoded by nucleic acids originating from biological samples, said methods comprising; (Y) retrieving from a first data-table information for a first nucleic acid, wherein said information comprises; (xv) a first combination of letters and/or numbers uniquely identifying the nucleic acid, and (xvi) the type of genetic element comprising said nucleic acid and (xvii) a second combination of letters and/or numbers uniquely identifying a clone in which a potential member encoded by said nucleic acid was tested for interaction with at least one other potential member of a pair or complex of interacting molecules (Z) using said second combination of letters and/or numbers to retrieve from said first data-table or optionally further data-tables, information identifying additional nucleic acids encoding for said at least one other potential member in step (xvii) . 70. The method of claim 69 further comprising using said second combination of letters and/or numbers in step (xvii) to retrieve from a second data-table further information, where said further information at least comprises the interaction class of said clone, and optionally additional information comprising, (AA) the physical location of the clone, (BB) predetermined experimental details pertaining to creation of said clone, including at least one of, (xviii) tissue, disease-state or cell source of the nucleic acid, (xix) cloning details, and (xx) membership of a library of other clones, 71. The method of claim 70 further comprising, using said information of step (Y) on said first and/or of step (Z) on additional nucleic acids to relate to a third data- table further characterising said first and/or additional nucleic acids, where said further characterising comprises at least one of (CC) hybridization data, (DD) oligonucleotide fingerprint data, (EE) nucleotide sequence, (FF) in-frame translation of the said nucleic acids, and (GG) tissue, disease-state or cell source gene expression data. optionally identifying the protein domain encoded by said first or additional nucleic acids. 72. The method of claim 71 further comprising, identifying if said potential members encoded by the nucleic acids interact, by considering said interaction class of said clone in which nucleic acids were tested for said interaction in step (Y) . 73. The method of one of claims 69 to 72, wherein said data relates to one or more of 10 to 100 potential members or 100 to 1000 potential members or 1000 to 10000 potential members or and more than 10,000 potential members. 74. The method of one of claims 69 to 73, wherein said data was generated by the method of claims 1 to 51. 75. The method of claims 70 to 74, wherein said interaction class comprises one of Positive, Negative or False Positive . 76. The method of one of claims 72 to 75 wherein sticky proteins are identified by consideration of the number of occurrences a given member is identified to interact with many different members in different clones of said positive interaction class. 77. The method of one of claims 69 to 76, wherein said first data-table forms part of a first database, and said second and third data tables form part of at least a second database. 78. The method of claim 77, wherein said second database is held on a computer readable memory separate from the computer readable memory holding said first database, and said database is accessed via a data exchange network. 79. The method of claim 78, wherein said second database comprises nucleic acid or protein sequence, secondary or tertiary structure, biochemical, biographical or gene expression information. 80. The method of claims 69 to 79, wherein data entry to said first, second or further data tables is controlled automatically from said first data base by access to other computer data, programs or computer controlled robots . 81. The method of one of claims 69 to 80, wherein at least one workflow management system is built around particular sets of data to assist in the progress of the method of claims 1 to 51. 82. The method of claim 81, wherein said workflow management system is software to assist in the progress of the identification of members of a pair or complex of interacting molecules using the method of hybridization as specified in claims 40 to 46. 83. The method of claims 69 to 82, wherein said data are investigated by queries of interest to an investigator. 84. The method of claim 83, wherein said queries include at least one of, (HH) identifying the interaction or interaction pathway between a first and second member of an interaction network; (II) identifying the interaction pathway between a first and second member of an interaction network and through at least one further member; (JJ) identifying the interaction or interaction pathway between at least two members characterised by nucleotide acid or protein sequences, secondary or tertiary structures, and (KK) identifying interactions or interaction pathways that are different for said different tissue, disease-state or cell source. 85. The method of claims 83 or 84, wherein parts of said information is stored in a controlled format to assist data query procedures . 86. The method of claims 83 to 85, wherein the results of said queries are displayed to the investigator in a graphical manner. 87. The method of claims 86, wherein a sub-set of data comprising data characterising nucleic acids identified as encoding members of a pair or complex of interacting molecules is stored in a further data-table or data base. 88. The method of claim 87 wherein consideration of the number of occurrences a given member is identified to interact with a second or further member is used to decide if said data characterising nucleic acids form part of said sub-set of data. 89. The method of claims 87 or 88, wherein additional information or experimental data is used to select those data to form part of said subset. 90. The method of claims 87 to 89, wherein to speed certain data query procedures, the structure in which the data is stored in the computer readable memory is modified. 91. The method of one of claims 69 to 90, wherein the data is held in relational or object oriented data bases. 92. A data storage scheme comprising a data table comprising a data table that holds information on each member of an interaction, where a record in said table represents each member of an interaction, and in which members are indicated to form interactions by sharing a common name. 93. The data storage scheme of claim 92, wherein said common name is a clone name or unique combination of letters and/or numbers comprising said clone name.

Inventors: BANCROFT DAVID, LEHRACH HANS, WANKER ERICH, WEDEMEYER NIELS, BANCROFT, DAVID, LEHRACH, HANS, WANKER, ERICH, WEDEMEYER, NIELS
Applicants: BANCROFT DAVID, LEHRACH HANS, MAX PLANCK GESELLSCHAFT, WANKER ERICH, WEDEMEYER NIELS, BANCROFT, DAVID, LEHRACH, HANS, MAX-PLANCK-GESELLSCHAFT ZUR FOERDERUNG DER WISSENSCHAFTEN E.V., WANKER, ERICH, WEDEMEYER, NIELS
Application year: 1998
Main classification: G01N33
IPC codes: A61K45, C12M1, C12N1, C12N5, C12N15, C12Q1, C40B30, G01N33, G06F17