Abstract:
Domains of epothilone polyketide synthase, and polynucleotides encoding therefor. Additionally, chimeric polyketide synthases that include domains, or subsets of domains, patterned on epothilone polyketide synthase. Methods to prepare epothilone in pharmaceutically useful quantitites are described, as are methods to prepare polyketide combinatorial libraries.

Description:
FIELD OF THE INVENTION 
     The present invention relates to polyketide synthase (&#34;PKS&#34;) enzymes that are capable of producing epothilone compounds. Epothilone (FIG. 4), is a polyketide antibiotic that also evidences antitumor activity. Epothilone was originally discovered based on antifungal activity identified in the myxobacterium Sorangium cellulosum (see K. Gerth et al., Journal of Antibiotics, 49, pp. 560-563, 1996). Given that it is difficult to produce such compounds by traditional chemical approaches, and that expression from wild-type myxobacteria is at levels too low for practical commercial use, there has been considerable interest in finding alternate means to produce these compounds. Accordingly, the present invention is directed to the production of PKS enzymes specific for epothilone, to polynucleotides that encode such synthases, and to host cells in which such encoding polynucleotides can be advantageously expressed. Further enhancements in the biological activities of epothilone, through production of derivatives thereof, is also made possible according to the practice of the invention. 
     A large variety of polyketides having a vide spectrum of useful biological activities are known, and further variations including those generated from combinatorial libraries are possible. As elaborated below, this nearly infinite design flexibility is made possible in part by the modular nature of polyketide synthases, which are actually highly ordered complexes of multiple catalytic domains organized into modules. Accordingly, further aspects of the present invention include, for example, (1) providing encoding DNA for a chimeric PKS that is substantially patterned on a non-epothilone producing enzyme, but which incorporates one or more functional domains of epothilone PKS; (2) providing an encoding DNA for a chimeric PKS that is substantially patterned on the epothilone-producing enzyme, but which includes one or more catalytic domains associated with other PKS species; and (3) the use of combinatorial or other technologies to further enhance the extent of PKS and polyketide libraries. 
     BACKGROUND OF THE INVENTION 
     Polyketides represent a large family of diverse compounds synthesized from 2-carbon units through a series of condensations and subsequent modifications. Polyketides occur in many types of organisms including fungi, and mycelial bacteria, in particular the actinomycetes. An appreciation for the wide variety of polyketide structures, and for their biological activities, may be gained upon review of the extensive art, for example, published International Patent Specifications WO 93/13663 and WO 95/08548; U.S. Pat. Nos. 5,098,837, 5,149,639, 4,874,748, 5,063,155; and the journal articles H. Fu et al., Biochemistry, 33, pp. 9321-9326, (1994); R. McDaniel et al., Science, 262, pp. 1546-1550, (1993); and J. Rohr, Angew. Chien. Illt. Ed. Engl. 34(8), pp.881-888, (1995). 
     Polyketides are synthesized in nature on polyketide synthases (&#34;PKS&#34;). These enyzmes, which are actually complexes of multiple enzyme activities, are in some ways similar to, but in other ways different from, the synthases which catalyze condensation of 2-carbon units in the biosynthesis of fatty acids. Two major types of PKS are known which are very different in their construction and mode of synthesis. These are commonly referred to as Type I or &#34;modular&#34; and Type II &#34;aromatic.&#34; 
     The PKS enzyme complexes that are generally the subject of the present invention, and epothilone-PKS in particular, are members of the group designated Type I or modular PKS. In this type of PKS, a set of separate catalytic active sites (each active site is termed a &#34;domain&#34;, and a set thereof is termed a &#34;module&#34;) exists for each cycle of carbon chain elongation and modification. Based on the general nature of PKS activities it is possible to determine from the molecular structure of epothilone that epothilone-PKS consists of 8 modules, although the number of polypeptides that provide the modules is unknown, as is the exact nature of the starter unit. 
     FIG. 9 of aforementioned W095/08548 depicts a typical genetic model for a Type I PKS, in this case for 6-deoxyerythronolide B synthase (&#34;DEBS&#34;) involved in the production of erythromycin. Six separate modules, each catalyzing a round of condensation and modification of a 2-carbon unit, are present. The number and type of catalytic domains that are present in each module varies (see the WO FIG. 9) based on the needed chemistry, and the total of 6 modules is provided on 3 separate polypeptides (designated DEBS-1, DEBS-2, and DEBS-3, with 2 modules per each). Each of the DEBS polypeptides is encoded from a separate open reading frame (gene), see Caffrey et al., FEBS Letters, 304, pp. 205, 1992. 
     The catalytic domains of the DEBS polypeptides provide a representative example of Type I PKS design. In this particular case, modules 1 and 2 reside on DEBS-1, modules 3 and 4 on DEBS-2, and modules 5 and 6 on DEBS-3, wherein module 1 is defined as the first module to act on the growing polyketide backbone, and module 6 the last. 
     The minimal PKS module is typified by module 3 which contains a ketosynthase (&#34;KS&#34;) domain, an acyltransferase (&#34;AT&#34;) domain, and an acyl carrier protein (&#34;ACP&#34;) domain. These three enzyme activities are sufficient to activate the 2-carbon extender unit and attach it to the growing polyketide molecule. Additional domains that may be included in a module relate to reactions other than the actual condensation, and include a ketoreductase activity (&#34;KR&#34;) activity, a dehydratase activity (&#34;DH&#34;), and an enoylreductase activity (&#34;ER&#34;). With respect to DEBS-1, the first module thereof also contains repeats of the AT and ACP activities because it catalyzes initial condensation, i.e. it begins with a &#34;loading domain&#34; represented by AT and ACP, which determine the nature of the starter unit. The &#34;finishing&#34; of the 6deoxyerythronolide molecule is regulated by a thioesterase activity (&#34;TE&#34;) in module 6. This thioesterase appears to catalyze cyclization of the macrolide ring thereby increasing the yield of the particular polyketide product. 
     In PKS polypeptides, the regions that encode enzymatic activities (domains) are separated by linker or &#34;scaffold&#34;-coding regions. These scaffold regions encode amino acid sequences that space the enzymatic activities (domains) at the appropriate distances and in the correct order. Thus, these linker regions collectively can be considered to encode a scaffold into which the various domains (and thus modules) are placed in a particular order and spatial arrangement. Generally, this organization permits PKS domains of different or identical substrate specificities to be substituted (usually at the level of encoding DNA) between PKS species by various available methodologies. Thus, there is considerable flexibility in the design of new PKS in order to produce novel polyketide pharmaceuticals. 
     An additional level of structural complexity in the resultant polyketides may be introduced by subsequent glycosylation or other post-PKS reactions. 
     SUMMARY OF THE INVENTION 
     As aforementioned, the polyketide antibiotic epothilone was first discovered based on its activity as an antifungal compound. Forms A and B thereof were isolated (see FIG. 4) differing in whether the R group at position 12 is hydrogen or methyl. It was subsequently determined that epothilone compounds have valuable activities as antitumor agents based on the microtubule stabilization mechanism previously recognized for taxol (see D. Bollag et al., Cancer Research, 55, pp. 2325-2333, 1995). Since epothilones evidence certain advantages over taxol (for example, greater solubility in water and greater efficacy against multi-drug resistant cells), there has been considerable interest in these compounds, and in methods to produce pharmaceutically useful quantities thereof. 
     In a first embodiment of the present invention, there are provided polynucleotides that comprise an encoding sequence for one or more domains of epothilone polyketide synthase, or a subset thereof. In a preferred example, the polynucleotide also comprises encoding sequence for one or more domains of another polyketide synthase. Expression of such encoding DNAs, typically in suitable host cells, leads to the production of useful quantities of chimeric synthases capable of producing valuable polyketides. 
     Accordingly, there is provided a chimeric polyketide synthase (PKS) wherein at least 10 consecutive amino acids in one or more domains of one or more modules thereof are derived from one or more domains of one or more modules of epothilone polyketide synthase. Preferably at least 15, and most preferably at least 20 consecutive amino acids are included. Representative epothilone PKS domains useful in this aspect of the invention include, for example, KR, DH, AT, and KS domains. In the usual case, an entire epothilone PKS domain is included in the chimeric PKS. 
     In the typical practice of the invention, the chimeric PKS is assembled from polypeptides encoded by DNA molecules that comprise encoding sequences for polyketide synthase domains, wherein at least one encoded domain includes at least 10 consecutive amino acids corresponding to a domain of epothilone polyketide synthase. In such DNA molecules the encoding seqeunces are operably linked to control sequences so that expression therefrom in host cells is effective. 
     Representative examples of amino acid sequences useful in constructing the chimeric PKS of the invention include, for example, the following sequences from epothilone PKS, that is: 
     SEQ ID NO:1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO:7, SEQ ID NO: 8, SEQ ID NO: 9 and SEQ ID NO:10. 
     These and other aspects of the present invention, including use of combinatorial approaches, are described according to the Detailed Description of the Invention, which follows directly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, panel A, shows a comparison of the amino acid sequence of certain polyketide ketoreductase (KR) domains (SEQ ID NOS: 18-20) with a region of an epothilone ketoreductase domain (SEQ ID NO:1) 
     FIG. 1, panel B, shows a comparison of the amino acid sequence from the erythromycin module 1 ketosynthase domain (DEBS KS1 fragment, SEQ ID NO:21) with regions of two epothilone ketosynthase domains (SEQ ID NOS: 3,5). 
     FIG. 2 shows a map of the the 45.3 kb cosmid pKos28-26. 
     FIG. 3 (panels A-H) provides an additional representation of the polynucleotide and amino acid sequences disclosed herein (SEQ ID NOS 1-14 as labeled). 
     FIG. 4 shows the structure of epothilone A and epothilone B. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Given the valuable pharmaceutical properties of epothilones, it is important to devise means by which pharmaceutically useful quantities thereof can be produced. As aforementioned, only limited quantities of epothilones can be recovered from microbial cells that normally produce such polyketides, and resort to synthetic methods is impractical. 
     According to the practice of the invention, purified and isolated DNA molecules are provided that comprise one or more encoding sequences for one or more domains of epothilone polyketide synthase. Examples of such encoded domains include epothilone polyketide synthase KR, DH, AT and KS domains as evidenced by the amino acid sequences disclosed herein as SEQ ID NOS: 1, 3, 5 and 7-10. The corresponding encoding sequences are disclosed herein as SEQ ID NOS: 2, 4, 6, and 11-14 respectively. 
     A further example of an encoding polynucleotide is represented by the complete sequences of cosmid pKos28-26 (see Example 2) that correspond to epothilone polyketide synthase domains and modules. 
     Upon determination of all of the encoding sequences for the epothilone polyketide synthase complex, and upon elucidation of the organization of domains and modules in the synthase polypeptides, appropriate DNA molecules may be constructed in which the complete set of appropriately arranged epothilone PKS-encoding sequences are operably linked to expression control sequences that are effective in suitable host cells. 
     Further aspects of the invention include: 
     (1) providing encoding DNA for a chimeric PKS that is substantially patterned on a non-epothilone producing enzyme, but which incorporates one or more functional domains of epothilone PKS; 
     (2) providing an encoding DNA for a chimeric PKS that is substantially patterned on the epothilone-producing enzyme, but which includes one or more catalytic domains associated with other PKS species; and 
     (3) the use of combinatorial or other technologies to further enhance the extent of PKS and polyketide libraries. 
     With respect to item (1) above, preferred examples include construction of chimeric PKS enzymes wherein the erythromycin PKS and rapamycin PKS function as accepting scaffolds, and one or more of the above-identified epothilone domains are inserted as replacements for domains of comparable function. Of course, construction of such enzymes is most effectively achieved by construction of appropriate encoding polynucleotides. In this regard, the examples of erythromycin PKS and rapamycin PKS are expected to be preferred given the low sequence homology between Sorangium and Streptomyces DNA, which is useful to avoid undesireable recombination events. In this example of the invention, it is not necessary to replace an entire domain of the scaffold PKS with an entire domain of epothilone PKS, rather peptide subsequences of a PKS domain that correspond to a peptide subsequence in a scaffold domain, or which otherwise provide useful function, may be used as replacements. Accordingly, appropriate encoding DNAs for construction of such chimeric PKS include those that encode at least 10, preferably 15, and most preferably 20 or more amino acids of a selected epothilone domain. 
     Additional information concerning construction and expression of encoding DNAs for the novel PKS of the invention, and concerning combinatorial approaches, is as follows. 
     Broadly, the invention provides recombinant materials for the production of combinatorial libraries of polyketides wherein the polyketide members of the library are synthesized by PKS systems derived from naturally occurring PKS systems that are used as scaffolds. Generally, many members of these libraries may themselves be novel compounds and the invention further includes novel polyketide members of these libraries. The invention methods may be directed to the preparation of an individual polyketide. The polyketide may or may not be novel, but the method of preparation permits a more convenient method of preparing it. The resulting polyketides may be further modified to convert them to antibiotics, typically, through glycosylation. 
     In another aspect, the invention is directed to a multiplicity of cell colonies comprising a library of colonies wherein each colony of the library contains an expression vector for the production of a different modular PKS, but derived from a naturally occurring PKS. In a preferred embodiment, the different PKS are derived from the erythromycin PKS. In any case, the library of different modular PKS is obtained by modifying one or more of the regions of a naturally occurring gene or gene cluster encoding an enzymatic activity so as to alter that activity, leaving intact the scaffold portions of the naturally occurring gene. Preferably, the replacing activity is represented by a domain of epothilone PKS or a subset thereof. The invention is also directed to methods to produce libraries of PKS complexes and to produce libraries of polyketides by culturing these colonies, as well as to the libraries so produced. In addition, the invention is directed to methods to screen the resulting polyketide libraries and to novel polyketides contained therein. 
     Regardless of the naturally occurring PKS gene used as a scaffold, the invention provides libraries or individual modified forms, ultimately of polyketides, by generating modifications in the erythromycin PKS or other naturally occurring PKS gene cluster so that the protein complexes produced by the cluster have altered activities in one or more respects, and thus produce polyketides other than the natural product of the PKS. Novel polyketides may thus be prepared, or polyketides in general prepared more readily, using this method. By providing a large number of different genes or gene clusters derived from a naturally occurring PKS gene cluster, each of which has been modified in a different way from the native cluster, an effectively combinatorial library of polyketides can be produced as a result of the multiple variations in these activities. Again, use of epothilone PKS domains is preferred. 
     In summary, a polyketide synthase &#34;derived from&#34; a naturally occurring PKS contains the scaffolding encoded by all the portion employed of the naturally occurring synthase gene, contains at least two modules that are functional, and contains mutations, deletions, or replacements of one or more of the activities of these functional modules so that the nature of the resulting polyketide is altered. This definition applies both at the protein and genetic levels. Particular preferred embodiments include those wherein a KS, AT, KR, DH or ER has been deleted or replaced by a version of the activity from a different PKS or from another location within the same PKS. Also preferred are derivatives where at least one noncondensation cycle enzymatic activity (KR, DH or ER) has been deleted or wherein any of these activities has been mutated so as to change the ultimate polyketide synthesized. 
     Thus, there are five degrees of freedom for constructing a polyketide synthase in terms of the polyketide that will be produced. First, the polyketide chain length will be determined by the number of modules in the PKS. Second, the nature of the carbon skeleton of the PKS will be determined by the specificities of the acyl transferases which determine the nature of the extender units at each position--e.g., malonyl, methyl malonyl, or ethyl malonyl, etc. Third, the loading domain specificity will also have an effect on the resulting carbon skeleton of the polyketide. Thus, the loading domain may use a different starter unit, such as acetyl, propionyl, and the like. Fourth, the oxidation state at various positions of the polyketide will be determined by the dehydratase and reductase portions of the modules. This will determine the presence and location of ketone, alcohol, alkene or alkane substituents at particular locations in the polyketide. Finally, the stereochemistry of the resulting polyketide is a finction of three aspects of the synthase. The first aspect is related to the AT/KS specificity associated with substituted malonyls as extender units, which affects stereochemistry only when the reductive cycle is missing or when it contains only a ketoreductase since the dehydratase would abolish chirality. Second, the specificity of the ketoreductase will determine the chirality of any β-OH. Finally, the enoyl reductase specificity for substituted malonyls as extender units will influence the result when there is a complete KR/DH/ER available. 
     Methods useful in support of construction of novel modular PKS are as follows. 
     A large number of modular PKS gene clusters have been mapped and/or sequenced. including for erythromycin and rapamycin, which have been completely mapped and sequenced, and for soraphen A, FK506 and oleandomycin which have been partially sequenced, and for candicidin, avermectin, and nemadectin which have been mapped and partially sequenced. Additional modular PKS gene clusters are expected to be available as time progresses. These genes can be manipulated using standard techniques to delete or inactivate activity encoding regions, insert regions of genes encoding corresponding activities from the same or different PKS systems, or be otherwise mutated using standard procedures for obtaining genetic alterations. Of course, portions of, or all of, the desired derivative coding sequences can be synthesized using standard solid phase synthesis methods such as those described by Jaye et al., J Biol Chem (i 984) 259:6331 and which are available commercially fron for example, Applied Biosystems, Inc. 
     In order to obtain nucleotide sequences encoding a variety of derivatives of the naturally occurring PKS, and thus a variety of polyketides for construction of a library, a desired number (97of constructs can be obtained by &#34;mixing and matching&#34; enzymatic activity-encoding portions, and mutations can be introduced into the native host PKS gene cluster or portions thereof. Use of encoding sequence for epothilone domains is preferred. 
     Mutations can be made to the native sequences using conventional techniques. The substrates for mutation can be an entire cluster of genes or only one or two of them; the substrate for mutation may also be portions of one or more of these genes. Techniques for mutation include preparing synthetic oligonucleotides including the mutations and inserting the mutated sequence into the gene encoding a PKS subunit using restriction endonuclease digestion. (See, e.g. , Kunkel, T. A. Proc Natl Acad Sci USA (1985) 82:448; Geisselsoder et al. Bio Techniques (1987) 5:786.) Alternatively, the mutations can be effected using a mismatched primer (generally 10-20 nucleotides in length) which hybridizes to the native nucleotide sequence (generally cDNA corresponding to the RNA sequence), at a temperature below the melting temperature of the mismatched duplex. The primer can be made specific by keeping primer length and base composition within relatively narrow limits and by keeping the mutant base centrally located. Zoller and Smith, Methods in Enzymology (1983) 100:468. Primer extension, is effected using DNA polymerase. The product of the extension reaction was cloned and those clones containing the mutated DNA were selected. Selection can be accomplished using the mutant primer as a hybridization probe. The technique is also applicable for generating multiple point mutations. See, e.g., Dalbie-McFarland et al. Proc Natl Acad Sci USA (1982) 79:6409. PCR mutagenesis will also find use for effecting the desired mutations. 
     Random mutagenesis of selected portions of the nucleotide sequences encoding enzymatic activities can be accomplished by several different techniques known in the art, e.g., by inserting an oligonucleotide linker randomly into a plasmid, by irradiation with X-rays or ultraviolet light, by incorporating incorrect nucleotides during in vitro DNA synthesis, by error-prone PCR mutagenesis, by preparing synthetic mutants or by damaging plasmid DNA in vitro with chemicals. Chemical mutagens include, for example, sodium bisulfite, nitrous acid, hydroxylamine, agents which damage or remove bases thereby preventing normal base-pairing such as hydrazine or formic acid, analogues of nucleotide precursors such as nitrosoguanidine, 5-bromouracil, 2-aminopurine, or acridine intercalating agents such as proflavine, acriflavine, quinacrine, and the like. Generally, plasmid DNA or DNA fragments are treated with chemicals, in transformed into E. coli and propagated as a pool or library of mutant plasmids. 
     In addition to providing mutated forms of regions encoding enzymatic activity, regions encoding corresponding activities from different PKS synthases or from different locations in the same PKS synthase can be recovered, for example, using PCR techniques with appropriate primers. By &#34;corresponding&#34; activity encoding regions is meant those regions encoding the same general type of activity--e.g., a ketoreductase activity in one location of a gene cluster would &#34;correspond&#34; to a ketoreductase-encoding activity in another location in the gene cluster or in a different gene cluster; similarly, a complete reductase cycle could be considered corresponding--e.g., KR/DH/ER would correspond to KR alone. 
     If replacement of a particular target region in a host polyketide synthase is to be made, this replacement can be conducted in vitro using suitable restriction enzymes or can be effected in vivo using recombinant techniques involving homologous sequences framing the replacement gene in a donor plasmid and a receptor region in a recipient plasmid. Such systems, advantageously involving plasmids of differing temperature sensitivities are described for example, in PCT application WO 96/40968. 
     The vectors used to perform the various operations to replace the enzymatic activity in the host PKS genes or to support mutations in these regions of the host PKS genes may be chosen to contain control sequences operably linked to the resulting coding sequences in a manner that expression of the coding sequences may be effected in a appropriate host. However, simple cloning vectors may be used as well. 
     If the cloning vectors employed to obtain PKS genes encoding derived PKS lack control sequences for expression operably linked to the encoding nucleotide sequences, the nucleotide sequences are inserted into appropriate expression vectors. This need not be done individually, but a pool of isolated encoding nucleotide sequences can be inserted into host vectors, the resulting vectors transformed or transfected into host cells and the resulting cells plated out into individual colonies. 
     Suitable control sequences include those which function in eucaryotic and procaryotic host cells. Preferred hosts include fungal systems such as yeast and procaryotic hosts, but single cell cultures of, for example, mammalian cells could also be used. There is no particular advantage, however, in using such systems. Particularly preferred are yeast and procaryotic hosts which use control sequences compatible with Streptomyces spp. Suitable controls sequences for single cell cultures of various types of organisms are well known in the art. Control systems for expression in yeast, including controls which effect secretion are widely available and are routinely used. Control elements include promoters, optionally containing operator sequences, and other elements depending on the nature of the host, such as ribosome binding sites. Particularly useful promoters for procaryotic hosts include those from PKS gene clusters which result in the production of polyketides as secondary metabolites, including those from aromatic (Type II) PKS gene clusters. Examples are act promoters, tcm promoters, spiramycin promoters, and the like. However, other bacterial promoters, such as those derived from sugar metabolizing enzymes, such as galactose, lactose (lac) and maltose, are also useful. Additional examples include promoters derived from biosynthetic enzymes such as for tryptophan (trp), the β-lactamase (bla), bacteriophage lambda PL, and T5. In addition, synthetic promoters, such as the tac promoter (U.S. Pat. No. 4,551,433), can be used. 
     Other regulatory sequences may also be desirable which allow for regulation of expression of the PKS replacement sequences relative to the growth of the host cell. Regulatory sequences are known to those of skill in the art, and examples include those which cause the expression of a gene to be turned on or off in response to a chemical or physical stimulus, including the presence of a regulatory compound. Other types of regulatory elements may also be present in the vector, for example, enhancer sequences. 
     Selectable markers can also be included in the recombinant expression vectors. A variety of markers are known which are useful in selecting for transformed cell lines and generally comprise a gene whose expression confers a selectable phenotype on transformed cells when the cells are grown in an appropriate selective medium. Such markers include, for example, genes which confer antibiotic resistance or sensitivity to the plasmid. Alternatively, several polyketides are naturally colored and this characteristic provides a built-in marker for screening cells successfully transformed by the present constructs. 
     The various PKS nucleotide sequences, or a cocktail of such sequences, can be cloned into one or more recombinant vectors as individual cassettes, with separate control elements, or under the control of, e.g., a single promoter. The PKS subunits or cocktail components can include flanking restriction sites to allow for the easy deletion and insertion of other PKS subunits or cocktail components so that hybrid PKSs can be generated. The design of such unique restriction sites is known to those of skill in the art and can be accomplished using the techniques described above, such as site-directed mutagenesis and PCR 
     As described above, particularly useful control sequences are those which themselves, or using suitable regulatory systems, activate expression during transition from growth to stationary phase in the vegetative mycelium. The system contained in the plasmid identified as pCK7, i.e., the actI/actIII promoter pair and the actII-ORF4 (an activator gene), is particularly preferred Particularly preferred hosts are those which lack their own means for producing polyketides so that a cleaner result is obtained. Illustrative host cells of this type include the modified S. coelicolor CH999 culture described in PCT application WO 96140968 and similar strains of S. lividans. 
     The expression vectors containing nucleotide sequences encoding a variety of PKS systems for the production of different polyketides are then transformed into the appropriate host cells to construct the library. In one straightforward approach, a mixture of such vectors is transformed into the selected host cells and the resulting cells plated into individual colonies and selected for successful transformants. Each individual colony will then represent a colony with the ability to produce a particular PKS synthase and ultimately a particular polyketide. Typically, there will be duplications in some of the colonies; the subset of the transformed colonies that contains a different PKS in each member colony can be considered the library. Alternatively, the expression vectors can be used individually to transform hosts, which transformed hosts are then assembled into a library. A variety of strategies might be devised to obtain a multiplicity of colonies each containing a PKS gene cluster derived from the naturally occurring host gene cluster so that each colony in the library produces a different PKS and ultimately a different polyketide. The number of different polyketides that are produced by the library is typically at least four, more typically at least ten, and preferably at least 20, more preferably at least 50, reflecting similar numbers of different altered PKS gene clusters and PKS gene products. The number of members in the library is arbitrarily chosen; however, the degrees of freedom outlined above with respect to the variation of starter, extender units, stereochemistry, oxidation state, and chain length is quite large. 
     Methods for introducing the recombinant vectors of the present invention into suitable hosts are known to those of skill in the art and typically include the use of CaCl 2  or other agents, such as divalent cations, lipofection, DMSO, protoplast transformation and electroporation. 
     As disclosed in the co-pending application entitled &#34;Production of Polyketides in Bacteria and Yeasts&#34; (of Phillip J. Barr et al., identified as Express Mail Label No. EH 493640115US, as filed on Dec. 11, 1997) incorporated herein by reference, a wide variety of hosts can be used, even though some hosts natively do not contain the appropriate post-translational mechanisms to activate the acyl carrier proteins of the synthases. These hosts can be modified with the appropriate recombinant enzymes to effect these modifications. 
     The polyketide producing colonies can be identified and isolated using known techniques and the produced polyketides further characterized. The polyketides produced by these colonies can be used collectively in a panel to represent a library or may be assessed individually for activity. 
     The libraries can thus be considered at four levels: (1) a multiplicity of colonies each with a different PKS encoding sequence encoding a different PKS cluster but all derived from a naturally occurring PKS cluster; (2) colonies which contain the proteins that are members of the PKS produced by the coding sequences; (3) the polyketides produced; and (4) antibiotics derived from the polyketides. Of course, combination libraries can also be constructed wherein members of a library derived, for example, from the erythromycin PKS can be considered as a part of the same library as those derived from, for example, the rapamycin PKS cluster. 
     Colonies in the library are induced to produce the relevant synthases and thus to produce the relevant polyketides to obtain a library of candidate polyketides. The polyketides secreted into the media can be screened for binding to desired targets, such as receptors, signaling proteins, and the like. The supernatants per se can be used for screening, or partial or complete purification of the polyketides can first be effected. Typically, such screening methods involve detecting the binding of each member of the library to receptor or other target ligand. Binding can be detected either directly or through a competition assay. Means to screen such libraries for binding are well known in the art. Alternatively, individual polyketide members of the library can be tested against a desired target. In this event, screens wherein the biological response of the target is measured can more readily be included. 
     EXAMPLES 
     Example 1 
     Identification of a Nucleotide Sequence Encoding a Ketoreductase (KR) Domain of Epothilone Polyketide Synthase 
     A culture of Sorangium cellulosum SMP44 was grown on agar plates using filter paper as carbon source. The cells were scraped from the plate, suspended in water, and collected by centrifugation. The cells were then resuspended in 1 ml of 25% sucrose, 1 mM EDTA, 0.5 M Tris-HCl, pH 7.8. A 450 μl aliquot of the suspension was mixed with 200 μl of 5% SDS, 125 mM EDTA, 0.5 M Tris-HCl, pH 7.6, and then treated with 3 μl of ribonuclease A (1 mg/ml). 
     After incubation of this mixture at 70° C. for 30 minutes, 100 μl of 5M potassium acetate was added, and the mixture was placed on ice for 15 minutes. Solids were removed by centrifugation, and the supernatant was extracted twice with equal volumes of phenol/chloroform. The genomic DNA was precipitated from the aqueous phase by addition of ethanol, and then redissolved in 10 mM Tris-HCl, 1 mM EDTA. 
     Primers derived from the published sequence of the soraphen polyketide synthase genes (see T. Schupp et al., Journal of Bacteriology, 177, pp. 3673-3679, 1995) were used to amplify ketoreductase sequences (KR) from the genomic DNA of SMP44. 
     The primers used were 
     
         (SEQ ID NO: 15)(forward): CGGATCCCAG GGCGTCGAGG AAGGCG(SEQ ID NO: 16)(reverse): GGAATTCATC ACCGGAGGCA CCGGC 
    
     The resultant PCR fragment was subcloned using the EcoRI and BamHI sites introduced by the PCR primers. Sequencing of the plasmid DNA form one resultant clone gave: 
     
         (SEQ ID NO: 17)GGATCCCATG GCGTCGAGGA AGGCGTTGGC GGCGGCGTAATTGGACTGGG CGGGGCTCCC GAGCACCCCG GAGAGCGACGAGAACAGGAC GAAGGCGCGC AGCGGGCTGT GGCGCGTCTGCTCGTCGAGG TTGACGGCCG CGTCGACCTT GGCCCGGAGCACGGCGCTCA GGCGCGCCGG CGTCATCGAG GAGAGCACGCCGTCGTCGAG TGTGCCTGCG GCGTGCACGA CGGCGGTCAGCGGCCTGTCG TGCGGGATGG CGAGCAGCAC CCGCTCGAGGGCGACGCGAT CGGCAGCGTC CGCGGCGGCG ACGACGACGGAGGCGCCGCG CGCCTGGAGC TCCGCGGCGA GGTCGGATGCGCCGGGAGCA TCCGGGCCCC GGCGCGAGAG CAGCACCAGGTGCTTGACGC CGTGGCGGTC GACGAGGCGA CGCGCCACGAGAGCGCCGAG GGTGCCGGTG CCTCCGGTGA TGAATTC 
    
     wherein nucleotide sequence corresponding to primers is underlined. 
     The resultant coding strand DNA, 
     
         (SEQ ID NO:2)gaattcatca ccggaggcac cggcaccctc ggcgctctcgtggcgcgtcg cctcgtcgac cgccacggcg tcaagcacctggtgctgctc tcgcgccggg gcccggatgc tcccggcgcatccgacctcg ccgcggagct ccaggcgcgc ggcgcctccgtcgtcgtcgc cgccgcggac gctgccgatc gcgtcgccctcgagcgggtg ctgctcgcca tcccgcacga caggccgctgaccgccgtcg tgcacgccgc aggcacactc gacgacggcgtgctctcctc gatgacgccg gcgcgcctga gcgccgtgctccgggccaag gtcgacgcgg ccgtcaacct cgacgagcagacgcgccaca gcccgctgcg cgccttcgtc ctgttctcgtcgctctccgg ggtgctcggg agccccgccc agtccaattacgccgccgcc aacgccttcc tcgacgccat gggatcc, 
    
     encodes amino acid sequence (SEQ ID NO:1) corresponding to a ketoreductase (KR) domain of epothilone polyketide synthase, as evidenced by its homology to known ketoreductase domain sequences. This is demonstrated by reference to FIG. 1, Panel A, which shows a comparison of known KR domain sequences from within certain PKS that produce soraphens (SEQ ID NOS: 18,19) and an erythromycin (SEQ ID NO: 20). Based on the structure of epothilone, all modules of the epothilone PKS, except No. 7, are expected to have KR domains. The module number to which SEQ ID NO: 1 corresponds has not yet been determined. 
     Example 2 
     Isolation and Structure of Cosmid pKos28-26 
     A general ketosynthase domain probe was generated from Sorangium cellulosum SMP44 chromosomal DNA using degenerate primers designed by alignment of ketosynthase (KS) domains from a number of polyketide synthases. The degenerate primers used were as follows, wherein bases are designated using art-recognized single letter designations as also provided for in 37 CFR 1.822(b)(1): 
     
         (SEQ ID NO: 22)primer 1: 5&#39;-RTG SGC RTT VGT NCC RCT-3&#39;(SEQ ID NO: 23)primer 2; 5&#39;-GAC ACV GCN TGY TCB TCV-3&#39; 
    
     wherein R=A and G; Y=C and T; S=G and C; B=G and T and C; N=A and G and C and T; and V=G and A and C. 
     The resultant PCT product was approximately 800 bp long, and was then non-radioactively labelled with DIG nucleotides (Boehringer Mannheim) for detection. A cosmid library of partial Sau3A digested chromosomal DNA fragments from Sorangium cellulosum SMP44 was generated in the Supercos system (Stratagene). The library was then screened by colony hybridization using the general KS domain probe. Cosmid pKos28-26 was identified as a cosmid that hybridized with the KS domain probe. In one set of experiments, sequences A, B, C and D in the cosmid (see FIG. 2) were conveniently studied because of the placement of Nsi I and Hind III restriction sites. Following use of the restriction enzymes, two small fragments (containing the A and B, and also the C and D regions, see FIG. 2) were subcloned and sequenced. Nucleotide sequences for cosmid regions A, B, C and D are reported herein as SEQ ID NOS: 11, 12, 13 and 14 respectively, and the amino acids encoded thereby as SEQ ID NOS: 7, 8, 9 and 10 respectively. 
     In general, encoding DNA for polyketide synthase modules ranges from about 3 to 5 kb (depending on the reductive cycle activities that are present), and in general have one of the following domain orders: 
     KS-AT-DH-ER-KR-ACP 
     KS-AT-DH-KR-ACP 
     KS-AT-KR-ACP 
     KS-AT-ACP. 
     Examination of the epothilone structure, based on art-recognized understandings of polyketide synthase reactions, predicts the presence of 8 synthase modules in the PKS, encoded by up to about 40 kb of DNA. Based on recognized sequence homologies, it was determined that: Sequence A codes for a DH and a KR domain region; Sequence B codes for a KS domain region, and also a region linking the KS to an AT domain region; Sequence C codes for an AT domain that is malonyl-CoA specific; and Sequence D codes for a DH domain region. 
     Reference to the map of the pKos28-26 cosmid thus indicates that at least 3 modules are represented, with Sequence A being near the end of one module, Sequence B being toward the middle of the next module, and Sequences C and D both being near the middle of the third module. 
     Example 3 
     Sequence Homology in Ketosynthase Domains 
     Additional fragments of encoding sequence for ketosynthase domains (KS) of epothilone polyketide synthase have also been isolated, and the corresponding amino acid sequences determined. FIG. 1, panel B, presents a comparison of these fragments (for SEQ ID NOS: 4, 6, which encode amino acid sequences represented by SEQ ID NOS: 3 and 5 respectively) to an erythromycin module 1 ketosynthase domain fragment (DEBS KS1, SEQ ID NO:21). The common amino acid element Cys-Ser-Ser-Ser-Leu (FIG. 1B, susbset of SEQ ID NOS: 3and 5) is a recognized active site motif within a KS domain, and Gly-Thr-Asn-Ala-His (FIG. 1B, susbset of SEQ ID NOS: 3and 5) is a recognized element marking the C-terminal end of such a domain. 
     
         __________________________________________________________________________#             SEQUENCE LISTING- &lt;160&gt; NUMBER OF SEQ ID NOS: 23- &lt;210&gt; SEQ ID NO 1&lt;211&gt; LENGTH: 159&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 1- Glu Phe Ile Thr Gly Gly Thr Gly Thr Leu Gl - #y Ala Leu Val Ala Arg#                 15- Arg Leu Val Asp Arg His Gly Val Lys His Le - #u Val Leu Leu Ser Arg#             30- Arg Gly Pro Asp Ala Pro Gly Ala Ser Asp Le - #u Ala Ala Glu Leu Gln#         45- Ala Arg Gly Ala Ser Val Val Val Ala Ala Al - #a Asp Ala Ala Asp Arg#     60- Val Ala Leu Glu Arg Val Leu Leu Ala Ile Pr - #o His Asp Arg Pro Leu# 80- Thr Ala Val Val His Ala Ala Gly Thr Leu As - #p Asp Gly Val Leu Ser#                 95- Ser Met Thr Pro Ala Arg Leu Ser Ala Val Le - #u Arg Ala Lys Val Asp#           110- Ala Ala Val Asn Leu Asp Glu Gln Thr Arg Hi - #s Ser Pro Leu Arg Ala#       125- Phe Val Leu Phe Ser Ser Leu Ser Gly Val Le - #u Gly Ser Pro Ala Gln#   140- Ser Asn Tyr Ala Ala Ala Asn Ala Phe Leu As - #p Ala Met Gly Ser145                 1 - #50                 1 - #55- &lt;210&gt; SEQ ID NO 2&lt;211&gt; LENGTH: 477&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 2- gaattcatca ccggaggcac cggcaccctc ggcgctctcg tggcgcgtcg cc - #tcgtcgac  60- cgccacggcg tcaagcacct ggtgctgctc tcgcgccggg gcccggatgc tc - #ccggcgca 120- tccgacctcg ccgcggagct ccaggcgcgc ggcgcctccg tcgtcgtcgc cg - #ccgcggac 180- gctgccgatc gcgtcgccct cgagcgggtg ctgctcgcca tcccgcacga ca - #ggccgctg 240- accgccgtcg tgcacgccgc aggcacactc gacgacggcg tgctctcctc ga - #tgacgccg 300- gcgcgcctga gcgccgtgct ccgggccaag gtcgacgcgg ccgtcaacct cg - #acgagcag 360- acgcgccaca gcccgctgcg cgccttcgtc ctgttctcgt cgctctccgg gg - #tgctcggg 420- agccccgccc agtccaatta cgccgccgcc aacgccttcc tcgacgccat gg - #gatcc 477- &lt;210&gt; SEQ ID NO 3&lt;211&gt; LENGTH: 250&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#throughout theORMATION: Xaa at various positions#unknown amino acidbe any, other or- &lt;400&gt; SEQUENCE: 3- Asp Thr Ala Cys Ser Ser Ser Leu Val Ser Le - #u His Leu Ala Cys Thr#                 15- Ala Leu Arg Gln Gly Glu Cys Asp Leu Ala Le - #u Thr Gly Gly Val Met#             30- Val Ile Thr Thr Pro Ala Gly Phe Val Xaa Ph - #e Ser Arg Ala Arg Gly#         45- Leu Ala Arg Asp Gly Arg Cys Lys Ser Phe Se - #r Ala Gln Ala Asp Gly#     60- Val Ile Trp Ser Glu Gly Cys Gly Met Leu Le - #u Leu Lys Arg Leu Ser# 80- Asp Ala Arg Arg Asp Arg Asp Arg Val Leu Gl - #y Val Ile Arg Gly Ser#                 95- Ala Val Asn Gln Asp Arg Arg Ser Gln Gly Le - #u Thr Ala Pro Asn Gly#           110- Pro Ala Gln Gln Arg Val Ile Arg Gln Ala Le - #u Ser Ser Cys Gly Leu#       125- Ser Pro Glu Asn Arg Arg Gly Gly Gly Ala Tr - #p Asp Gly Thr Ser Leu#   140- Gly Asp Pro Ile Glu Ala Gly Ala Leu Ala Gl - #u Val Phe Gly Pro Glu145                 1 - #50                 1 - #55                 1 -#60- Arg Ser Pro Glu Arg Pro Leu Tyr Leu Gly Se - #r Ser Lys Ser Asn Leu#               175- Gly His Ala Gln Ala Ala Ala Gly Val Ala Gl - #y Val Ile Lys Met Val#           190- Leu Ala Leu Gln His Glu Val Leu Pro Lys Th - #r Leu His Ala Glu Gln#       205- Pro Ser Pro His Ile Ala Trp Glu Gly Ser Gl - #y Leu Ser Leu Leu Gln#   220- Glu Ala Arg Pro Trp Arg Arg Asn Gly Arg Va - #l Arg Arg Ala Gly Val225                 2 - #30                 2 - #35                 2 -#40- Ser Ser Phe Gly Ile Ser Gly Thr Asn Ala#               250- &lt;210&gt; SEQ ID NO 4&lt;211&gt; LENGTH: 751&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 4- gacacggctt gttcgtcgtc gctggtgtcg ctgcacctgg cgtgcacggc gc - #tgcgccag  60- ggcgaatgcg acctggcgct gaccggcggg gtgatggtga tcaccacccc cg - #cgggattc 120- gtttagttca gtcgtgcccg ggggcttgcg cgagacggtc ggtgcaagag ct - #tctctgcc 180- caggctgacg gcgtcatctg gtccgaaggg tgcgggatgc tgttgctgaa gc - #ggctgtct 240- gacgcgcggc gcgaccgcga ccgtgtgctg ggggtgatcc gtggctctgc gg - #tgaaccag 300- gaccgtcgca gccagggtct gacggcgccg aacggccctg cccagcagcg gg - #tgatccgg 360- caggcgctgt cgtcgtgtgg tctgtcgccc gagaatcgac gcggtggagg cg - #catgggac 420- ggtacgagcc tcggagaccc gatcgaggcc ggagcgctgg cggaggtgtt tg - #gaccggag 480- cgtagccccg agcgtccgct gtacctgggg tcgtcgaagt cgaacctggg ac - #atgcgcag 540- gcggccgcgg gtgtggcggg cgtgatcaag atggtgctgg cgctgcagca cg - #aggtgctg 600- ccgaagacgc tgcatgcgga gcagccgagc ccgcacatcg cgtgggaggg ga - #gcgggctg 660- tcattgctgc aagaggcgcg tccgtggcgg cgcaacggcc gggtccgtcg tg - #ccggcgtg 720#         751      gcgg aactaacgcc c- &lt;210&gt; SEQ ID NO 5&lt;211&gt; LENGTH: 197&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#throughout theORMATION: Xaa at various positions#unknown amino acidbe any, other or- &lt;400&gt; SEQUENCE: 5- Phe Phe Gly Cys Gln Ala Glu Arg Ala Arg Al - #a Gly Pro Arg Val Ala#                 15- Gly Met Leu Leu Leu Lys Ala Ala Val Xaa Ar - #g Ala Ala Arg Arg Arg#             30- Pro Cys Ala Gly Val Ile Arg Gly Ser Ala Va - #l Asn Gln Asn Val Ala#         45- Ala Arg Phe Xaa Trp Arg Arg Thr Ala Leu Pr - #o Ser Ser Gly Xaa Ser#     60- Gly Arg Ala Leu Ser Ser Cys Gly Leu Ser Pr - #o Glu Asp Ile Asp Ala# 80- Val Glu Ala His Gly Thr Gly Thr Ser Leu Gl - #y Asp Pro Ile Glu Ala#                 95- Gly Ala Leu Ala Glu Val Phe Gly Pro Glu Ar - #g Ser Pro Glu Arg Pro#           110- Leu Tyr Leu Gly Ser Ser Lys Ser Asn Leu Gl - #y His Ala Gln Ala Ala#       125- Ala Gly Val Ala Gly Val Ile Lys Met Val Le - #u Ser Met Gln His Glu#   140- Val Leu Pro Lys Thr Leu His Ala Glu Gln Pr - #o Ser Pro His Ile Gly145                 1 - #50                 1 - #55                 1 -#60- Trp Glu Gly Ser Gly Leu Ser Leu Leu Gln Gl - #u Ala Arg Pro Trp Arg#               175- Arg Asn Gly Arg Val Arg Arg Ala Gly Val Se - #r Ser Phe Gly Ile Ser#           190- Gly Thr Asn Ala His   195- &lt;210&gt; SEQ ID NO 6&lt;211&gt; LENGTH: 591&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 6- ttcttcggtt gccaggcgga acgggcgcgg gctgggccga gggttgcggg aa - #tgctgttg  60- ttgaaagcgg ctgtctgacg cgcagcgcga cggcgaccgt gtgctggggt ga - #tccgtggc 120- tctgcggtga accagaacgt cgcagccagg ttctgatggc gccgaacggc cc - #tgcccagc 180- agcgggtgat ccggcagggc gctgtcgtcg tgtggtctgt cgcccgagga ca - #tcgacgcg 240- gtggaggcgc acggtacggg cacgagcctt ggagacccga tcgaggccgg ag - #cgctggcg 300- gaggtgtttg gaccggagcg tagccccgag cgtccgctgt acctgggatc gt - #cgaagtcg 360- aacctcggac atgcgcaggc ggcggcgggc gtggcgggcg tgatcaagat gg - #tgctgtcg 420- atgcagcacg aggtgctgcc gaagacgctg cacgcggagc agccgagccc gc - #acattggg 480- tgggaaggaa gcgggctgtc gctgctgcaa gaggcgcgtc cgtggcggcg ca - #acggccgg 540#            591gcgtgtc gtcgttcggg atcagcggaa ctaacgcgca c- &lt;210&gt; SEQ ID NO 7&lt;211&gt; LENGTH: 260&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#throughout theORMATION: Xaa at various positions#unknown amino acidbe any, other or- &lt;400&gt; SEQUENCE: 7- Ala Leu Arg Ala Trp Ile Glu Arg Gly Ala Pr - #o Thr Pro Val Arg Val#                 15- Val Ile Asp Thr Asn Ala Ala Ser Ser Pro Ar - #g Ser Asp Val Ala Gly#             30- Ser Ser His Glu Ala Thr Arg Gln Ala Leu Se - #r Leu Leu Gln Ala Trp#         45- Leu Ser Glu Pro Arg Leu Asp Ala Val Xaa Le - #u Val Trp Val Thr Arg#     60- Gly Ala Val Ser Ala Ala Pro Asp Asp Ala Va - #l Xaa Asp Leu Ala His# 80- Gly Pro Leu Trp Gly Leu Ile Arg Thr Ala Ar - #g Ser Glu His Pro Glu#                 95- Arg Arg Leu Arg Leu Ile Asp Val Gly Thr Xa - #a Pro Val Asp Thr Gly#           110- Leu Leu Ala Xaa Ala Leu Ala Thr Ala Ala Gl - #u Pro Glu Leu Ala Leu#       125- Pro Arg Gly Pro Xaa Trp Pro Pro Ala Gly Se - #r Xaa Xaa Pro His Arg#   140- Lys Thr His Pro Thr Pro Arg Leu Asp Leu Pr - #o Ala Pro Xaa Cys Xaa145                 1 - #50                 1 - #55                 1 -#60- Xaa Asn Leu Gly Arg Leu Gly Xaa Ala Xaa As - #n Pro Ser Cys Ser Pro#               175- Xaa Arg Val Xaa Ala Pro Phe Ser Xaa Leu Pr - #o Pro Gly Ala Xaa Ser#           190- Pro Arg Ala Pro Asn Phe Ser Ile Leu Gln Gl - #u Xaa Ala Pro Lys Pro#       205- Phe Asn Val Ala Ser Ile Phe Asn Arg Lys As - #n Ser Pro Xaa Cys Arg#   220- Ile Xaa Pro Ala Pro Leu Thr Val Leu Pro Ar - #g Xaa Val Ser Xaa Gly225                 2 - #30                 2 - #35                 2 -#40- Phe Gln Thr Lys Pro Thr Xaa Cys Leu Ala Ly - #s Val Arg Ala Pro Leu#               255- Xaa Ile Thr Asn       260- &lt;210&gt; SEQ ID NO 8&lt;211&gt; LENGTH: 249&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#throughout theORMATION: Xaa at various positions#unknown amino acidbe any, other or- &lt;400&gt; SEQUENCE: 8- Thr Lys Leu Arg Pro Lys Pro Xaa Xaa Arg Va - #l Thr Thr Gly Phe Phe#                 15- Val Gly Phe Xaa Arg Lys Leu Xaa Gly Xaa Xa - #a Gln Glu Arg His Xaa#             30- Leu Glu Xaa Asp Xaa Ala Gly Arg Leu Gly Ly - #s Xaa Ser Xaa Leu Xaa#         45- Lys Xaa Ser Asn Arg Glu Pro Trp Xaa Xaa Gl - #u Val Asn Leu Gly Xaa#     60- Arg Lys Val Arg Ala Xaa Asn Arg Val Phe Ly - #s Met Cys Cys Ser Met# 80- Gln His Glu Xaa Leu Pro Lys Thr Xaa Arg Ar - #g Ser Ser Xaa Ala Gly#                 95- His Trp Trp Arg Glu Arg Ala Phe Val Ala Al - #a Arg Gly Ala Ser Val#           110- Ala Ala Gln Arg Pro Gly Ala Ala Arg Gly Ar - #g Val Val Val Arg Ile#       125- Ser Gly Thr Asn Ala His Val Ile Leu Glu Gl - #u Ala Pro Val Glu Ala#   140- Ala Arg Glu Pro Val Glu Ala Val Arg Glu Pr - #o Val Glu Ala Glu Gly145                 1 - #50                 1 - #55                 1 -#60- Val Ala Ile Pro Leu Leu Leu Ser Gly Arg As - #p Glu Ala Ser Val Ala#               175- Ala Gln Ala Gly Arg Trp Ala Lys Trp Leu Gl - #u Glu His Gly Glu Val#           190- Gly Trp Ser Asp Val Val Arg Thr Ala Ala Le - #u His Arg Thr His Phe#       205- Glu Ser Arg Ala Ser Val Leu Ala Ala Ser Al - #a Ala Gly Ala Val Glu#   220- Gly Leu Arg Ala Leu Ser Ser Gly Arg Pro As - #p Ala Ala Val Val Ser225                 2 - #30                 2 - #35                 2 -#40- Gly Thr Ala Lys Arg Gly Gly Lys Leu           245- &lt;210&gt; SEQ ID NO 9&lt;211&gt; LENGTH: 222&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#throughout theORMATION: Xaa at various positions#unknown amino acidbe any, other or- &lt;400&gt; SEQUENCE: 9- Lys Leu Ala Val Leu Phe Thr Gly Gln Gly Se - #r Gln Arg Leu Gly Met#                 15- Gly Lys Arg Leu Tyr Glu Val Tyr Pro Val Ph - #e Arg Ala Ala Phe Asp#             30- Glu Val Cys Glu Ala Leu Asp Ala His Leu As - #p Arg Gly Leu Arg Xaa#         45- Val Val Phe Ala Ala Ala Gly Ser Glu Glu Xa - #a Ala Gln Leu Glu Arg#     60- Thr Glu Tyr Thr Gln Pro Gly Leu Phe Ala Le - #u Glu Val Ala Leu Tyr# 80- Arg Gln Trp Xaa Ser Trp Gly Leu Asn Pro Le - #u Arg Cys Trp Gly Thr#                 95- Arg Xaa Glu Xaa Xaa Thr Leu Arg Thr Xaa Ar - #g Val Xaa Xaa Xaa Leu#           110- Arg Thr Gln Xaa Thr Xaa Val Pro Pro Xaa Se - #r Ala Asp Gln Gly Phe#       125- Gln Xaa Arg Gly Thr Met Phe Pro Xaa Lys Pr - #o Pro Asn Pro Lys Xaa#   140- Thr Gly Xaa Ser Lys Ser Gly Gln Gly His Xa - #a Leu Pro Gly Xaa Pro145                 1 - #50                 1 - #55                 1 -#60- Pro Ser Thr Ser Asn Xaa Thr Asn Ala Phe Xa - #a Val Ala His Ala Glu#               175- Pro Gly Arg Pro Pro Leu Ser Phe Xaa Leu Pr - #o Pro His Xaa Glu Xaa#           190- Lys Ile Glu Val Pro Ile Leu Pro Pro Leu Ar - #g Val Pro Xaa Ala Pro#       205- Cys Lys Thr Asn Xaa Ile Val Asp Xaa Xaa Gl - #y Pro Lys Asn#   220- &lt;210&gt; SEQ ID NO 10&lt;211&gt; LENGTH: 264&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#throughout theORMATION: Xaa at various positions#unknown amino acidbe any, other or- &lt;400&gt; SEQUENCE: 10- Gly Lys Xaa Xaa Xaa Leu Val Lys Phe Ala Xa - #a Ile Phe Gly Asn Ala#                 15- Gly Gly Asp Phe Val Gly Pro Asn Arg Gly Gl - #y Cys Leu Val Xaa Xaa#             30- His Arg Thr Gly Arg Asn Xaa Xaa Gly Gln Xa - #a Glu Gly Val Xaa Arg#         45- Arg Thr Leu Pro Leu Pro Gly Val Asp Glu Le - #u Xaa Xaa Ala His Ser#     60- Xaa Xaa Gly Gly Xaa Asp Phe Ser Gly Phe Th - #r Arg Val Asp Glu Val# 80- Ile Arg Leu Arg Pro Ala Phe Gln Gly Leu Tr - #p Ser Xaa Arg Xaa Xaa#                 95- Thr Asp Phe Phe Arg Pro Gly Val Phe Ala Gl - #n Arg Arg Asp Glu Gln#           110- Arg Arg Gly Leu Arg Val His Pro Ala Xaa Me - #t Asn Xaa Ala Leu His#       125- Thr Met Phe Ala Ala Phe Ala Glu Val Ser Al - #a Pro Xaa Asp Val Leu#   140- Leu Xaa Phe Ser Cys Ser Xaa Val Ala Leu Hi - #s Ala Thr Gly Ala Ser145                 1 - #50                 1 - #55                 1 -#60- Glu Xaa Arg Val Arg Leu Glu Xaa Ala Gly Gl - #y Arg Asp Ser Ala Gln#               175- Ala Ala Ala Ser Leu Arg Val Thr Asp Ala Al - #a Gly Gln Pro Val Val#           190- Ser Val Gly Ala Leu His Leu Arg Arg Ala Th - #r Ala Glu Gln Leu Arg#       205- Ala Ala Thr His Ala Glu Ala Gln His Leu Ty - #r Arg Val Asp Phe Gln#   220- Leu Val Ser Leu Val Glu Ala Gly Ser Lys Va - #l Asp Ser Leu Val Val225                 2 - #30                 2 - #35                 2 -#40- Leu Arg Ala Pro Glu Gly Arg Gly Arg Leu Gl - #y Glu Ala Leu Gly Val#               255- Glu Ala Ile Ala Gly Leu Asp Ala       260- &lt;210&gt; SEQ ID NO 11&lt;211&gt; LENGTH: 787&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:&lt;223&gt; OTHER INFORMATION: &#34;n&#34; at various posi - #tions throughout the#other or unknowny be A, T, C, G,- &lt;400&gt; SEQUENCE: 11- atgcattgcg cgcttggatc gagcggggcg cgccaacgcc tgtgcgggtg gt - #gatcgaca  60- cgaacgctgc cagctcaccg cgctcggacg tggcggggtc gtcgcacgag gc - #gacgaggc 120- aggcgctgtc gctgctgcaa gcgtggttgt cggagccgcg gctcgacgct gt - #cganctgg 180- tgtgggtgac gcggggcgcg gtcagcgcag ctccggacga cgccgtcgan ga - #cctggcgc 240- acgggccgct gtgggggctt attcgcacgg cgcgcagcga gcaccccgag cg - #ccggctgc 300- gcttgatcga tgtggggacc gancccgtgg acactgggct gctggcgcng gc - #gctggcga 360- cggcggcgga accngaactt gccctgcccc ggggcccgtn ctggcccccc gc - #tggttccn 420- tacngccgca ccgaaaaact cacccaaccc cccggctgga ccttccggca cc - #tncttgtt 480- nacngaacct tggccgtctt gggcnagcgt naaacccntc ttgttccccc nc - #ncgggttt 540- aagcaccttt ttctnaactt ccccccgggg cctgaagccc ccgggccccc aa - #cttttcaa 600- tcctccaaga aancgcccca aaacctttca atgttgcttc aattttcaac cg - #gaaaaatt 660- cccccttntg ccggattaan ccggcccccc taaccgttct nccccgctng gt - #ttcaaang 720- gttttcaaac naagccaacc ncttgtttgg ccaaggtaag ggcncccctc cn - #aataacga 780#         787- &lt;210&gt; SEQ ID NO 12&lt;211&gt; LENGTH: 750&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:&lt;223&gt; OTHER INFORMATION: &#34;n&#34; at various posi - #tions throughout the#other or unknowny be A, T, C, G,- &lt;400&gt; SEQUENCE: 12- tgnaccaagc taaggccgaa gcccngcann agggtaacna caggcttttt tg - #tnggtttt  60- ncccgaaaat taangggngn ggnncaggaa cggcacnccc tngaantcga tt - #gagccgga 120- cgnttgggga agntttcggn cttggncaag cngagcaacc gtgaaccttg gt - #tnntggaa 180- gtgaaccttg gcangcgcaa ggttcgggcg gntaaccggg tgttcaagat gt - #gctgttcg 240- atgcagcacg agntgctgcc gaagacgtgn aggcggagca gcngagccgg nc - #attggtgg 300- agggagcggg ctttcgttgc tgcaagaggc gcgtccgtgg cggcgcaacg gc - #cgggcgcg 360- gcgcgcgggc gtgtcgtcgt tcggatcagc gggacgaacg cccatgtcat cc - #tcgaagag 420- gcgccggtgg aggcggctcg cgagccggtg gaggcggtgc gcgagccggt gg - #aggcggag 480- ggtgttgcga taccgctgtt gctgtcgggg cgagacgagg cctcggtggc gg - #cgcaggcg 540- gggcggtggg cgaagtggct ggaagagcac ggggaggtgg ggtggtcgga cg - #tggtgagg 600- acggcggcgc tgcaccggac gcacttcgag tcgcgggcgt cggtgcttgc gg - #cgagcgct 660- gcgggagctg tggagggtct tcgcgcgctg tcgtcggggc ggccggatgc gg - #cggtggtg 720#          750     gagg cgggaagctt- &lt;210&gt; SEQ ID NO 13&lt;211&gt; LENGTH: 667&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:&lt;223&gt; OTHER INFORMATION: &#34;n&#34; at various posi - #tions throughout the#other or unknowny be A, T, C, G,- &lt;400&gt; SEQUENCE: 13- aagcttgcgg tgctgttcac ggggcagggc agccagcggc tcgggatggg ga - #agaggctt  60- tacgaagtgt accccgtgtt ccgtgcggcg ttcgacgagg tgtgcgaggc gc - #tggacgcg 120- catctcgacc gtgggttgag agangtggtg ttcgcggccg cgggcagcga gg - #aangagcg 180- cagctggagc ggacggagta cacgcagccc gggctgtttg cgctggaagt gg - #cgctgtac 240- cgtcagtggg antcgtgggg gctgaacccg ctgcgctgct ggggcactcg at - #angaaanc 300- tgaacgctgc gcacgtngcg ggtntnctga nccttgcgga cgcagcnaac ta - #ntgtnccc 360- ccgcngtcng ctgatcaagg gttccaagnc cggggaacca tgtttccgtn ga - #agcctccg 420- aacccgaagt ncaccggcnc ttcgaagtcn ggccagggcc acnaactccc cg - #gctaaccc 480- ccatccacgt ctaacnggac aaacgcgttc nccgttgccc acgctgagcc cg - #gccgcccc 540- ccgctttctt ttncccttcc accccatnac gaacngaaaa tcgaagtccc ga - #ttcttccc 600- cccctgcgtg taccntangc accctgcaaa accaattnca ttgttgattn ca - #anggcccc 660#         667- &lt;210&gt; SEQ ID NO 14&lt;211&gt; LENGTH: 794&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:&lt;223&gt; OTHER INFORMATION: &#34;n&#34; at various posi - #tions throughout the#other or unknowny be A, T, C, G,- &lt;400&gt; SEQUENCE: 14- nggcaagngc ngggntttgg ttaaattcgc ccntattttc ggaaatgccg gg - #ggtgattt  60- tgttgggccc aaccggggng ggtgtttggt tnaanaccac cgnacaggac gg - #aatncccn 120- tggtcaanag gaaggggttt nacgaagaac cttgccactt ccgggagttg at - #gagctaan 180- anttgcccat tccnggcncg gaggcgntga cttttcgggt tttacgaggg tt - #gatgaggt 240- gattcggtta cgcccggcct tccagggttt gtggagctnt cgnntcgana cg - #gacttttt 300- tcgcccgggt gtttttgccc aaagacggga cgaacagcgc cgaggattac gg - #gtgcatcc 360- ggcgntgatg aacnccgcgt tgcatacgat gttcgcagcg tttgcggagg ta - #tcagcgcc 420- ggangacgtg ctgctgcntt tttcgtgttc ggangtggcg ttgcacgcca cg - #ggggcgag 480- cgagntccgg gtgaggctgg agntcgcagg aggcagagac tcggcacagg ca - #gccgcntc 540- gctgcgcgtt acagatgccg ccggccagcc ggtggtgagc gtcggtgccc tg - #catctgcg 600- ccgggcgacg gccgagcagc tgcgggcagc gacgcatgcc gaggcgcagc ac - #ctgtaccg 660- ggtggacttc cagctcgtga gcctcgtgga ggcgggctcg aaggtggact cg - #ctggtggt 720- gctccgtgcg cctgaggggc gagggcgact gggcgaagcg ctgggtgtgg ag - #gcgatcgc 780#    794- &lt;210&gt; SEQ ID NO 15&lt;211&gt; LENGTH: 26&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 15#              26  gagg aaggcg- &lt;210&gt; SEQ ID NO 16&lt;211&gt; LENGTH: 25&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 16#               25 ggca ccggc- &lt;210&gt; SEQ ID NO 17&lt;211&gt; LENGTH: 477&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 17- ggatcccatg gcgtcgagga aggcgttggc ggcggcgtaa ttggactggg cg - #gggctccc  60- gagcaccccg gagagcgacg agaacaggac gaaggcgcgc agcgggctgt gg - #cgcgtctg 120- ctcgtcgagg ttgacggccg cgtcgacctt ggcccggagc acggcgctca gg - #cgcgccgg 180- cgtcatcgag gagagcacgc cgtcgtcgag tgtgcctgcg gcgtgcacga cg - #gcggtcag 240- cggcctgtcg tgcgggatgg cgagcagcac ccgctcgagg gcgacgcgat cg - #gcagcgtc 300- cgcggcggcg acgacgacgg aggcgccgcg cgcctggagc tccgcggcga gg - #tcggatgc 360- gccgggagca tccgggcccc ggcgcgagag cagcaccagg tgcttgacgc cg - #tggcggtc 420- gacgaggcga cgcgccacga gagcgccgag ggtgccggtg cctccggtga tg - #aattc 477- &lt;210&gt; SEQ ID NO 18&lt;211&gt; LENGTH: 158&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 18- Leu Leu Ile Thr Gly Gly Thr Gly Ala Ala Gl - #y Ala His Val Ala Arg#                 15- Trp Leu Ala Arg Glu Gly Ala Glu His Leu Va - #l Leu Ile Ser Arg Arg#             30- Gly Ala Gln Ala Glu Gly Ala Ser Glu Leu Hi - #s Ala Glu Leu Thr Ala#         45- Leu Gly Ala Arg Val Thr Phe Ala Ala Cys As - #p Val Ala Asp Arg Ser#     60- Ala Val Ala Thr Leu Leu Glu Gln Leu Asp Al - #a Glu Gly Ser Gln Val# 80- Arg Ala Val Phe His Ala Gly Gly Ile Gly Ar - #g His Ala Pro Leu Ala#                 95- Ala Thr Ser Leu Met Glu Leu Ala Asp Val Va - #l Ser Ala Lys Val Leu#           110- Gly Ala Gly Asn Leu His Asp Leu Leu Gly Pr - #o Arg Pro Leu Asp Ala#       125- Phe Val Leu Phe Ser Ser Ile Ala Gly Val Tr - #p Gly Gly Gly Gln Gln#   140- Ala Gly Tyr Ala Ala Gly Asn Ala Phe Leu As - #p Ala Leu Ala145                 1 - #50                 1 - #55- &lt;210&gt; SEQ ID NO 19&lt;211&gt; LENGTH: 158&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 19- Val Leu Ile Thr Gly Gly Thr Gly Thr Leu Gl - #y Ala Leu Val Ala Arg#                 15- Arg Leu Val Val Asn His Asp Ala Lys His Le - #u Leu Leu Thr Ser Arg#             30- Gln Gly Ala Ser Ala Pro Gly Ala Asp Val Le - #u Arg Ser Glu Leu Glu#         45- Ala Leu Gly Ala Ser Val Thr Leu Ala Ala Cy - #s Asp Val Ala Asp Pro#     60- Arg Ala Leu Lys Asp Leu Leu Asp Asn Ile Pr - #o Ser Ala His Pro Val# 80- Ala Ala Val Val His Ala Ala Ser Val Leu As - #p Gly Asp Leu Leu Gly#                 95- Ala Met Ser Leu Glu Arg Ile Asp Arg Val Ph - #e Ala Pro Lys Ile Asp#           110- Ala Ala Trp His Leu His Gln Leu Thr Gln As - #p Lys Pro Leu Ala Ala#       125- Phe Ile Leu Phe Ser Ser Val Ala Gly Val Le - #u Gly Ser Ser Gly His#   140- Ser Asn Tyr Ala Ala Ala Ser Ala Phe Leu As - #p Ala Leu Ala145                 1 - #50                 1 - #55- &lt;210&gt; SEQ ID NO 20&lt;211&gt; LENGTH: 158&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 20- Val Leu Val Thr Gly Gly Thr Gly Gly Val Gl - #y Gly Gln Ile Ala Arg#                 15- Trp Leu Ala Arg Arg Gly Ala Pro His Leu Le - #u Leu Val Ser Arg Ser#             30- Gly Pro Asp Ala Asp Gly Ala Gly Glu Leu Va - #l Ala Glu Leu Glu Ala#         45- Leu Gly Ala Arg Thr Thr Val Ala Ala Cys As - #p Val Thr Asp Arg Glu#     60- Ser Val Arg Glu Leu Leu Gly Gly Ile Gly As - #p Asp Val Pro Leu Ser# 80- Ala Val Phe His Ala Ala Ala Thr Leu Asp As - #p Gly Thr Val Asp Thr#                 95- Leu Thr Gly Glu Arg Ile Glu Arg Ala Ser Ar - #g Ala Lys Val Leu Gly#           110- Ala Arg Asn Leu His Glu Leu Thr Arg Glu Le - #u Asp Leu Thr Ala Phe#       125- Val Leu Phe Ser Ser Phe Ala Ser Ala Phe Gl - #y Ala Pro Gly Leu Gly#   140- Gly Tyr Ala Pro Gly Asx Ala Tyr Leu Asp Gl - #y Leu Ala Gln145                 1 - #50                 1 - #55- &lt;210&gt; SEQ ID NO 21&lt;211&gt; LENGTH: 249&lt;212&gt; TYPE: PRT&lt;213&gt; ORGANISM: Sorangium cellulosum- &lt;400&gt; SEQUENCE: 21- Asp Thr Ala Cys Ser Ser Ser Leu Val Ala Va - #l His Leu Ala Cys Gln#                 15- Ser Leu Arg Arg Gly Glu Ser Ser Leu Ala Me - #t Ala Gly Gly Val Thr#             30- Val Met Pro Thr Pro Gly Met Leu Val Asp Ph - #e Ser Arg Met Asn Ser#         45- Leu Ala Pro Asp Gly Arg Cys Lys Ala Phe Se - #r Ala Gly Ala Asn Gly#     60- Phe Gly Met Ala Glu Gly Ala Gly Met Leu Le - #u Leu Glu Arg Leu Ser# 80- Asp Ala Arg Arg Asn Gly Pro Val Leu Ala Va - #l Leu Arg Gly Thr Ala#                 95- Val Asn Ser Asp Gly Ala Ser Asn Gly Leu Se - #r Ala Pro Asn Gly Arg#           110- Ala Gln Val Arg Val Ile Gln Gln Ala Leu Al - #a Glu Ser Gly Leu Gly#       125- Pro Ala Asp Ile Asp Ala Val Glu Ala His Gl - #y Thr Gly Thr Arg Leu#   140- Gly Asp Pro Ile Glu Ala Arg Ala Leu Phe Gl - #u Ala Tyr Gly Arg Asp145                 1 - #50                 1 - #55                 1 -#60- Arg Glu Gln Pro Leu His Leu Gly Ser Val Ly - #s Ser Asn Leu Gly His#               175- Thr Gln Ala Ala Ala Gly Val Ala Gly Val Il - #e Lys Met Val Leu Ala#           190- Met Arg Ala Gly Thr Leu Pro Arg Thr Leu Hi - #s Ala Ser Glu Arg Ser#       205- Lys Glu Ile Asp Trp Ser Ser Gly Ala Ile Se - #r Leu Leu Asp Glu Pro#   220- Glu Pro Trp Pro Ala Gly Ala Arg Pro Arg Ar - #g Ala Gly Val Ser Ser225                 2 - #30                 2 - #35                 2 -#40- Phe Gly Ile Ser Gly Thr Asn Ala His           245- &lt;210&gt; SEQ ID NO 22&lt;211&gt; LENGTH: 18&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#may be A, T, C or GION: &#34;n&#34; at position 13- &lt;400&gt; SEQUENCE: 22#  18              ct- &lt;210&gt; SEQ ID NO 23&lt;211&gt; LENGTH: 18&lt;212&gt; TYPE: DNA&lt;213&gt; ORGANISM: Sorangium cellulosum&lt;220&gt; FEATURE:#may be A, T, C or GION: &#34;n&#34; at position 9- &lt;400&gt; SEQUENCE: 23#  18              cv__________________________________________________________________________