METHODS FOR ISOLATING NOVEL ANTIMICROBIAL AGENTS FROM HYPERMUTABLE MAMMALIAN CELLS

Abstract: Dominant-negative alleles of human mismatch repair genes can be used to generate hypermutable cells and organisms. By introducing these genes into mammalian cells new cell lines with novel and useful properties can be prepared more efficiently than by relying on the natural rate of mutation or introduction of mutations by chemical mutagens. These methods are useful for generating novel and highly active antimicrobial molecules as well as superior antimicrobial agents from pre-existing chemicals. These methods are also useful for generating cell lines expressing novel antimicrobials that are useful for pharmaceutical manufacturing.

Description: METHODS FOR ISOLATING NOVEL ANTIMICROBIAL AGENTS FROM HYPERMUTABLE MAMMALIAN CELLS FIELD OF THE INVENTION The present invention is related to the area of antimicrobial agents and cellular production of those agents. In particular, it is related to the field of identification of novel antimicrobial agents by placing mammalian cells under selection in the presence ofthe microbe. BACKGROUND OF THE INVENTION For as long as man has shared the planet with microorganisms there have been widespread outbreaks of infectious disease and subsequent widespread mortality associated with it. Although microorganisms and man frequently share a symbiotic relationship, microorganisms can, under some conditions, lead to sickness and death. The discovery, wide use and dissemination of antibiotics to treat microbial infection in both human and animal populations over the last one hundred or so years has done much to control, and in some instances, eradicate some microbes and associated infectious disease. However, microbes have a strong propensity to evolve and alter their genetic makeup when confronted with toxic substances that place them under life and death selective pressures. Therefore, emerging infectious diseases currently pose an important public health problem in both developed as well as developing countries. Not only have microbes evolved to evade and defeat current antibiotic therapeutics, but also there are novel and previously unrecognized and/or characterized bacterial, fungal, viral, and parasitic diseases that have emerged within the past two decades. Sass, Curr. Opin. in DrugDiscov. & Develop. 2000, 3(5):646-654. Since the accidental discovery of a penicillin-producing mold by Fleming there has been steady progress in synthesizing, isolating and characterizing new and more effective beta-lactam antibiotics. In addition to the great success ofthe beta-lactam family of antibiotics, the newer fluoroquinolones have a broad-spectrum of bactericidal activity as well as excellent oral bio-availability, tissue penetration and favorable safety and tolerability profiles. King et al. , Am. Fam. Physician, 2000, 61 , 2741 -2748. A newly devised four-generation classification ofthe quinolone drugs accounts for the expanded antimicrobial spectrum ofthe more recently introduced fluoroquinolones and their clinical indications. The so-called first generation drugs, which include nalidixic acid, are capable of achieving minimal serum levels. The second-generation quinolones, such as ciprofloxacin, have an increased gram-negative and systemic activity. The third-generation drugs comprise pharmaceuticals such as levofloxacin and are have significant and expanded action against gram-positive bacteria and atypical pathogens. Finally, the fourth- generation quinolone drugs, which, to date, only includes trovofloxacin, are highly active against anaerobes in addition to the activity described for the third-generation drugs. Furthermore, the quinolone class of anti-microbial drugs can be divided based on their pharmacokinetic properties and bioavailability. Mammalian epithelial surfaces are remarkable for their ability to provide critical physiologic functions in the face of frequent microbial challenges. The fact that these mucosal surfaces remain infection-free in the normal host suggests that highly effective mechanisms of host defense have evolved to protect these environmentally exposed tissues. Throughout the animal and plant kingdoms, endogenous genetically encoded antimicrobial peptides have been shown to be key elements in the response to epithelial compromise and microbial invasion. Zasloff, Curr. Opin. Immunol, 1992, 4, 3-7; and Bevins, Ciba Found. Symp., 1994, 186, 250-69. In mammals, a variety of such peptides have been identified, including the well-characterized defensins and cathelicidins and others (andropin, magainin, tracheal antimicrobial peptide, and PR-39; see Bevins, Ciba Found. Symp., 1994, 186, 250-69 and references therein). A major source of these host defense molecules is circulating phagocytic leukocytes. However, more recently, it has been shown that resident epithelial cells ofthe skin and respiratory, alimentary, and genitourinary tracts also synthesize and release antimicrobial peptides. Both in vitro and in vivo data support the hypothesis that these molecules are important contributors to intrinsic mucosal immunity. Alterations in their level of expression or biologic activity can predispose the organism to microbial infection. Huttner et αl., Pediαtr. Res., 1999, 45, 785- 94. Across the evolutionary scale species from insects to mammals to plants defend themselves against invading pathogenic microorganisms by utilizing cationic antimicrobial peptides that rapidly kill microbes without exerting toxicity to the host. Physicochemical peptide-lipid interactions provide attractive mechanisms for innate immunity as discussed below. Many of these peptides form cationic amphipathic secondary structures, typically alpha-helices and beta-sheets, which can selectively interact with anionic bacterial membranes via electrostatic interactions. Rapid, peptide-induced membrane permeabilization and subsequent cellular lysis is the result. Matsuzaki, Biochim. Biophys. Ada, 1999, 1462, 1-10. The primary structures of a large number of these host-defense peptides have been determined. While there is no primary structure homology, the peptides are characterized by a preponderance of cationic and hydrophobic amino acids. The secondary structures of many ofthe host-defense peptides have been determined by a variety of techniques. Sitaram et al, Biochim, Biophys. Acta, 1999, 1462, 29-54. The acyclic peptides tend to adopt helical conformation, especially in media of low dielectric constant, whereas peptides with more than one disulfide bridge adopt beta-structures. As described above, one reason for the rise in microbial drug resistance to the first line antimicrobial therapies in standard use today is the inappropriate and over-use of prescription antibiotics. Although bacteria are the most common organisms to develop drug-resistance, there are numerous examples of demonstrated resistance in fungi, viruses, and parasites. The development of a resistant phenotype is a complex phenomenon that involves an interaction ofthe microorganism, the environment, and the patient, separately as well as in combination. Sitaram et al, Biochim. Biophys. Acta, 1999, 1462, 29-54. The microorganism in question may develop resistance while under antibiotic selection or it may be a characteristic ofthe microbe prior to exposure to a given agent. There are a number of mechanisms of resistance to antibiotics that have been described, including genes that encode antibiotic resistance enzymes that are harbored on extrachromosomal plasmids as well as DNA elements (e.g. transposable elements) that can reside either extra- chromosomally or within the host genome. Due to the ability of microorganisms to acquire the ability to develop resistance to antibiotics there is a need to continually develop novel antibiotics. Traditional methods to develop novel antibiotics have included medicinal chemistry approaches to modify existing antibiotics (Kang etal, Bioorg. Med. Chem. Lett, 2000, 10, 95-99) as well as isolation of antibiotics from new organisms (Alderson et al, Res. Microbiol, 1993, 144, 665-12). Each of these methods, however, has limitations. The traditional medicinal chemistry approach entails modification of an existing molecule to impart a more effective activity. The chemist makes a "best guess" as to which parts ofthe molecule to alter, must then devise a synthetic strategy, synthesize the molecule, and then have it tested. This approach is laborious, requires large numbers of medicinal chemists and frequently results in a molecule that is lower in activity than the original antibiotic. The second approach, isolation of novel antimicrobial agents, requires screening large numbers of diverse organisms for novel antimicrobial activity. Then, the activity must be isolated from the microorganism. This is not a small task, and frequently takes many years of hard work to isolate the active molecule. Even after the molecule is identified, it may not be possible for medicinal chemists to effectively devise a synthetic strategy due to the complexity of he molecule. Furthermore, the synthetic strategy must allow for a cost-effective synthesis. Therefore, a method that would allow for creation of more effective antibiotics from existing molecules or allow rapid isolation of novel antimicrobial agents is needed to combat the ever-growing list of antibiotic resistant organisms. The present invention described herein is directed to the use of random genetic mutation of a cell to produce novel antibiotics by blocking the endogenous mismatch repair activity of a host cell. The cell can be a mammalian cell that produces an antimicrobial agent naturally, or a cell that is placed under selective pressure to obtain a novel antimicrobial molecule that attacks a specific microbe. Moreover, the invention describes methods for obtaining enhanced antimicrobial activity of a cell line that produces an antimicrobial activity due to recombinant expression or as part ofthe innate capacity ofthe cell to harbor such activity. In addition, the generation of genetically altered host cells that are capable of secreting an antimicrobial activity, which can be protein or non-protein based, will be valuable reagents for manufacturing the entity for clinical studies. An embodiment ofthe invention described herein is directed to the creation of genetically altered host cells with novel and/or increased antimicrobial production that are generated by a method that interferes with the highly ubiquitous and phylogenetically conserved process of mismatch repair. The present invention facilitates the generation of novel antimicrobial agents and the production of cell lines that express elevated levels of antimicrobial activity. Advantages ofthe present invention are further described in the examples and figures described herein. SUMMARY OF THE INVENTION One embodiment ofthe present invention provides a method for generating genetically altered mammalian cells and placing the cells under direct microbial selection as a means to isolate novel antimicrobial agents. Another embodiment provides a method for identifying novel microbe-specific toxic molecules by altering the ability ofthe cell to correct natural defects that occur in the DNA during the process of DNA replication. Interference with this process, called mismatch repair, leads to genetically dissimilar sibling cells. These genetically dissimilar cells contain mutations, ranging from one mutation/genome to two or more mutations/genome, offer a rich population of cells from which to select for specific output traits, such as the novel ability to resist microbial insult. The genetically altered cell generated by manipulation ofthe mismatch repair process is then incubated with a microbe that is normally toxic to cells. Most ofthe cells will rapidly lose viability and die; however, a subset of resistant cells will have the capacity to resist the microbial insult. These cells express a molecule, protein or non-protein in structure, that imbues an antimicrobial activity to the newly selected mammalian clones. These newly created cells can be expanded in vitro and the new molecule isolated and characterized by standard methods that are well described it the art. The novel molecule(s) are then tested for their ability to kill or inhibit the growth ofthe microbe by standard microbial assays that are well described in the art. Finally, the novel cell line generated serves as an additional resource for large-scale production ofthe novel antimicrobial agent for use in clinical studies. The processes described herein are applicable to any mammalian cell and any microbe for which an antibiotic agent is sought. The invention provides methods for rendering mammalian cells hypermutable as a means to generate antimicrobial agents. The invention also provides methods for generating genetically altered cell lines that secrete enhanced amounts of a known or novel antimicrobial polypeptide. The invention also provides methods for generating genetically altered cell lines that secrete enhanced amounts of a known or novel antimicrobial non-polypeptide based molecule. The invention also provides methods for generating genetically altered cell lines that do not secrete enhanced amounts of an antimicrobial peptide or non-peptide molecule but rather have a cell-surface active molecule that detoxifies the microbe under test. The invention also provides methods for producing an enhanced rate of genetic hypermutation in a mammalian cell and use of this as the basis to select for microbial- resistant cell lines. The invention also provides methods of mutating a known antimicrobial encoding gene of interest in a mammalian cell as a means to obtain a molecule with enhanced bactericidal activity. The invention also provides methods for creating genetically altered antimicrobial molecules in vivo. The invention also provides methods for creating novel antimicrobial molecules from pre-existing antimicrobial molecules by altering the innate enzymatic or binding ability ofthe molecules by altering the mismatch repair system within the host mammalian cell. The invention also provides methods for creating a novel anti-microbial polypeptide or non-polypeptide based molecule that has the capacity to bind in an irreversible manner to a microbe and thereby block binding ofthe pathogenic microbe to a host target organism and result in loss of viability ofthe microbe. The invention also provides methods for creating a novel antimicrobial polypeptide or non-polypeptide based small molecule that can block microbial cell growth and/or survival. The invention also provides methods for creating a novel antimicrobial polypeptide or non-polypeptide based biochemical that are able to irreversibly bind to toxic chemicals produced by pathogenic microbes. The invention also provides methods for creating genetically altered antimicrobial molecules, either peptide of non-peptide based, that have enhanced pharmacokinetic properties in host organisms. The invention also provides methods for creating genetically altered cell lines that manufacture an antimicrobial molecules, either peptide of non-peptide based, for use in large-scale production ofthe antimicrobial agent for clinical studies. These and other aspects ofthe invention are described in the embodiments below. In one embodiment ofthe invention described, a method for making a microbial-sensitive mammalian cell microbe resistant by rendering the cell line hypermutable is provided. A polynucleotide encoding a dominant negative allele of a mismatch repair gene is introduced into an mammalian cell. The cell becomes hypermutable as a result ofthe introduction ofthe gene. In another embodiment ofthe invention, an isolated hypermutable cell is provided. The cell comprises a dominant negative allele of a mismatch repair gene. The cell exhibits an enhanced rate of hypermutation. In another embodiment ofthe invention, an isolated hypermutable cell is provided. The cell comprises a dominant negative allele of a mismatch repair gene. The cell exhibits an enhanced rate of hypermutation. The populations of cells generated by introduction ofthe mismatch repair gene are grown in the presence of microbes that are toxic to the wild type non-mutant cells. Cells are selected that are resistant to the microbe and the novel molecule(s) isolated and characterized for antimicrobial activity by standard methods well described in the art. In another embodiment ofthe invention, an isolated hypermutable cell is described to create a novel antimicrobial molecule from a pre-existing antimicrobial molecule by altering the innate enzymatic or binding ability ofthe molecule. In another embodiment ofthe invention, a method of creating a novel antimicrobial, polypeptide or non-polypeptide based molecule that has the capacity to bind in an irreversible manner to a microbe and thereby block binding ofthe pathogenic microbe to a host target organism and result in loss of viability ofthe microbe. In another embodiment ofthe invention, a method of creating a novel antimicrobial polypeptide or non-polypeptide based small molecule that can block microbial cell growth and/or survival is described. In another embodiment ofthe invention, a method of creating a novel antimicrobial polypeptide or non-polypeptide based biochemical that are able to irreversibly bind to toxic chemicals produced by pathogenic microbes is described. In another embodiment ofthe invention, a method is provided for introducing a mutation into a known endogenous gene encoding for an antimicrobial polypeptide or a non-protein based antimicrobial molecule as a means to create a more efficacious antimicrobial. A polynucleotide encoding a dominant negative allele of a mismatch repair gene is introduced into a cell. The cell becomes hypermutable as a result ofthe introduction ofthe gene. The cell further comprises an antimicrobial gene(s) of interest. The cell is grown and tested to determine whether the gene encoding for an antimicrobial is altered and whether the novel molecule is more active by standard microbiology assays well known in the art. In another embodiment ofthe invention, a gene or genes encoding for an antimicrobial molecule is introduced into a mammalian cell host that is mismatch repair defective. The cell is grown, and then clones are analyzed for enhanced antimicrobial characteristics. In another embodiment ofthe invention, a method is provided for producing new phenotypes of a cell. A polynucleotide encoding a dominant negative allele of a mismatch repair gene is introduced into a cell. The cell becomes hypermutable as a result ofthe introduction ofthe gene. The cell is grown and tested for the expression of new phenotypes where the phenotype is enhanced secretion of a novel or known antimicrobial polypeptide. In another embodiment ofthe invention, a method is provided for producing new phenotypes of a cell. A polynucleotide encoding a dominant negative allele of a mismatch repair gene is introduced into a cell. The cell becomes hypermutable as a result ofthe introduction ofthe gene. The cell is grown and tested for the expression of new phenotypes where the phenotype is enhanced secretion of a novel or known antimicrobial non-polypeptide based molecule. In another embodiment ofthe invention, a method is provided for producing new phenotypes of a cell. A polynucleotide encoding a dominant negative allele of a mismatch repair gene is introduced into a cell. The cell becomes hypermutable as a result ofthe introduction ofthe gene. The cell is grown and tested for the expression of new phenotypes where the phenotype is enhanced antimicrobial activity of a novel or known antimicrobial polypeptide that is not secreted. In another embodiment ofthe invention, a method is provided for producing new phenotypes of a cell. A polynucleotide encoding a dominant negative allele of a mismatch repair gene is introduced into a cell. The cell becomes hypermutable as a result ofthe introduction ofthe gene. The cell is grown and tested for the expression of new phenotypes where the phenotype is enhanced antimicrobial activity of a novel or known antimicrobial non-polypeptide based molecule that is not secreted. In another embodiment ofthe invention, a method is provided for restoring genetic stability in a cell containing a polynucleotide encoding a dominant negative allele of a mismatch repair gene. The expression ofthe dominant negative mismatch repair gene is suppressed and the cell is restored to its former genetic stability. In another embodiment ofthe invention, a method is provided for restoring genetic stability in a cell containing a polynucleotide encoding a dominant negative allele of a mismatch repair gene and a newly selected phenotype. The expression of the dominant negative mismatch repair gene is suppressed and the cell restores its genetic stability and the new phenotype is stable. These and other embodiments ofthe invention provide the art with methods that generate enhanced mutability in cells and animals as well as providing cells and animals harboring potentially useful mutations and novel protein and non-protein based molecules. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a representative in situ β-galactosidase staining of TK-hPMS2-134 or TKvect cells to measure for cells containing genetically altered β-galactosidase genes; arrows indicate Blue (β-galactosidase positive) cells. Figure 2 is a schematic representation of sequence of alterations ofthe β- galactosidase gene produced by expression of TK-hPMS2-134 host cells in TK cells. Figures 3A, 3B and 3C show a representative immunoprecipitation of in vitro translated hPMS2 and hMLHl proteins. Figure 4 shows representative complementation of MMR activity in transduced SH cells. Figure 5 is a representative photograph of Syrian hamster TK-tsl3 cells transfected with a eukaryotic expression vector that produces a novel anti-microbial polypeptide. Figure 6 is a representative graph showing TK-hPMS-134 transfected TK cells can suppress the growth of bacteria in vitro. The presented invention is directed to, in part, methods for developing hypermutable mammalian cells by taking advantage ofthe conserved mismatch repair process of host cells. Mismatched repair process is described in several references. Baker et. al, Cell, 1995, 82, 309-319; Bronner et. al, Nature, 1994, 368, 258-261; de Wind et. al, Cell, 1995, 82, 321-330; and Drummond et. al, Science, 1995, 268, 1909-1912. Dominant negative alleles of such genes, when introduced into cells or transgenic animals, increase the rate of spontaneous mutations by reducing the effectiveness of DNA repair and thereby render the cells or animals hypermutable. Hypermutable cells or animals can then be utilized to develop new mutations in a gene of interest or in a gene whose function has not been previously described. Blocking mismatch repair in cells such as, for example, mammalian cells or mammalian cells transfected with genes encoding for specific antimicrobial peptides or non-peptide based antimicrobials, can enhance the rate of mutation within these cells leading to clones that have novel or enhanced antimicrobial activity or production and/or cells that contain genetically altered antimicrobials with enhanced biochemical activity against a range of opportunistic microbes. The process of mismatch repair, also called mismatch proofreading, is carried out by protein complexes in cells ranging from bacteria to mammalian cells. Modrich, Science, 1994, 266, 1959-1960. A mismatch repair gene is a gene that encodes for one ofthe proteins of such a mismatch repair complex. Baker et. al. , Cell, 1995, 82, 309-319; Bronner et. al, Nature, 1994, 368, 258-261; de Wind et. al, Cell, 1995, 82, 321-330; Drummond et. al, Science, 1995, 268, 1909-1912; and Modrich, Science, 1994, 266, 1959-1960. Although not wanting to be bound by any particular theory of mechanism of action, a mismatch repair complex is believed to detect distortions ofthe DNA helix resulting from non-complementary pairing of nucleotide bases. The non-complementary base on the newer DNA strand is excised, and the excised base is replaced with the appropriate base that is complementary to the older DNA strand. In this way, cells eliminate many mutations, which occur as a result of mistakes in DNA replication. Dominant negative alleles cause a mismatch repair defective phenotype even in the presence of a wild-type allele in the same cell. An example of a dominant negative allele of a mismatch repair gene is the human gene hPMS2-134, which carries a truncation mutation at codon 134. Nicolaides et. al, Mol Cell. Biol, 1998, 18, 1635-1641. The mutation causes the product of this gene to abnormally terminate at the position ofthe 134th amino acid, resulting in a shortened polypeptide containing the N-terminal 133 amino acids. Such a mutation causes an increase in the rate of mutations that accumulate in cells after DNA replication. Expression of a dominant negative allele of a mismatch repair gene results in impairment of mismatch repair activity, even in the presence ofthe wild- type allele. Any allele, which produces such effect, can be used in this invention. Dominant negative alleles of a mismatch repair gene can be obtained from the cells of humans, animals, yeast, bacteria, or other organisms. ProUa et. al, Science, 1994, 264, 1091-1093; Strand et. al, Nature, 1993, 365, 274-276; and Su et al, J. Biol. Chem., 1988, 263, 6829-6835. Screening cells for defective mismatch repair activity can identify such alleles. Cells from animals or humans with cancer can be screened for defective mismatch repair. Cells from colon cancer patients may be particularly useful. Parsons et. al, Cell, 1993, 75, 1227-1236; and Papadopoulos et. al, Science, 1993, 263, 1625-1629. Genomic DNA, cDNA, or mRNA from any cell encoding a mismatch repair protein can be analyzed for variations from the wild type sequence. Perucho, Biol. Chem., 1996, 377, 675-684. Dominant negative alleles of a mismatch repair gene can also be created artificially, for example, by producing variants ofthe hPMS2-134 allele or other mismatch repair genes. Various techniques of site-directed mutagenesis can be used. The suitability of such alleles, whether natural or artificial, for use in generating hypermutable cells or animals can be evaluated by testing the mismatch repair activity caused by the allele in the presence of one or more wild-type alleles, to determine if it is a dominant negative allele. A cell or an animal into which a dominant negative allele of a mismatch repair gene has been introduced will become hypermutable. This means that the spontaneous mutation rate of such cells or animals is elevated compared to cells or animals without such alleles. The degree of elevation ofthe spontaneous mutation rate can be at least 2- fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1000-fold that of the normal cell or animal. According to one aspect ofthe invention, a polynucleotide encoding a dominant negative form of a mismatch repair protein is introduced into a cell. The gene can be any dominant negative allele encoding a protein that is part of a mismatch repair complex, for example, PMS2,.PMS1, MLHl, or MSH2. The dominant negative allele can be naturally occurring or made in the laboratory. The polynucleotide can be in the form of genomic DNA, cDNA, RNA, or a chemically synthesized polynucleotide. The polynucleotide can be cloned into an expression vector containing a constitutively active promoter segment (such as but not limited to CMV, SV40, Elongation Factor or LTR sequences) or to inducible promoter sequences such as the steroid inducible pIND vector (In vitrogen), where the expression ofthe dominant negative mismatch repair gene can be regulated. The polynucleotide can be introduced into the cell by transfection. Transfection is any process whereby a polynucleotide is introduced into a cell. The process of transfection can be carried out in a living animal, e.g., using a vector for gene therapy, or it can be carried out in vitro, e.g. , using a suspension of one or more isolated cells in culture. The cell can be any type of eukaryotic cell, including, for example, cells isolated from humans or other primates, mammals or other vertebrates, invertebrates, and single celled organisms such as protozoa, yeast, or bacteria. In general, transfection will be carried out using a suspension of cells, or a single cell, but other methods can also be applied as long as a sufficient fraction ofthe treated cells or tissue incorporates the polynucleotide so as to allow transfected cells to be grown and utilized. The protein product ofthe polynucleotide may be transiently or stably expressed in the cell. Techniques for transfection are well known and available techniques for introducing polynucleotides include but are not limited to electroporation, transduction, cell fusion, the use of calcium chloride, and packaging ofthe polynucleotide together with lipid for fusion with the cells of interest. Once a cell has been transfected with the mismatch repair gene, the cell can be grown and reproduced in culture. If the transfection is stable, such that the gene is expressed at a consistent level for many cell generations, then a cell line results. An isolated cell is a cell obtained from a tissue of humans or animals by mechanically separating out individual cells and transferring them to a suitable cell culture medium, either with or without pretreatment ofthe tissue with enzymes, e.g., collagenase or trypsin. Such isolated cells are typically cultured in the absence of other types of cells. Cells selected for the introduction of a dominant negative allele of a mismatch repair gene may be derived from a eukaryotic organism in the form of a primary cell culture or an immortalized cell line, or may be derived from suspensions of single-celled organisms. The invention described herein is useful for creating microbial-resistant mammalian cells that secrete new antimicrobial biochemical agents, either protein or non- protein in nature. Furthermore, the invention can be applied to cell lines that express known antimicrobial agents as a means to enhance the biochemical activity ofthe antimicrobial agent. Once a transfected cell line has been produced, it can be used to generate new mutations in one or more gene(s) of interest or in genes that have not been previously described. A gene of interest can be any gene naturally possessed by the cell line or introduced into the cell line by standard methods known in the art. An advantage of using transfected cells or to induce mutation(s) in a gene or genes of interest that encode antimicrobial activity is that the cell need not be exposed to mutagenic chemicals or radiation, which may have secondary harmful effects, both on the object ofthe exposure and on the workers. Furthermore, it has been demonstrated that chemical and physical mutagens are base pair specific in the way they alter the structure of DNA; the invention described herein results in mutations that are not dependent upon the specific nucleotide or a specific string of nucleotides and is a truly random genetic approach. Therefore, use of the present invention to obtain mutations in novel or known antimicrobial genes will be much more efficient and have a higher likelihood of success in contrast to conventional mutagenesis with chemical or irradiation. Once a new antimicrobial trait is identified in a sibling cell, the dominant negative allele can be removed from the cell by a variety of standard methods known in the art. For example, the gene can be directly knocked out the allele by technologies used by those skilled in the art or use of a inducible expression system; the dominant-negative allele is driven by a standard promoter that is regulated by inclusion of an inducer, withdrawal ofthe inducer results in attenuation ofthe expression of the dominant negative mismatch repair mutant and a normal DNA repair process will ensue. New antimicrobial agents are selected from cells that have been exposed to the dominant negative mismatch repair process followed by incubating the mutant cells in the presence ofthe microbe for which an novel antimicrobial agent is sought. The novel antimicrobial agent is purified by standard methods known to those skilled in the art and characterized. The antimicrobial agents are re-screened to determine the specific activity of the novel antimicrobial as well as tested against a broad range of microbes to determine spectrum of activity. The gene(s) that encode the novel antimicrobial are isolated by standard well known methods to those in the art. The mutations can be detected by analyzing for alterations in the genotype ofthe cells by examining the sequence of genomic DNA, cDNA, messenger RNA, or amino acids associated with the gene of interest. A mutant polypeptide can be detected by identifying alterations in electrophoretic mobility, spectroscopic properties, or other physical or structural characteristics of a protein encoded by a mutant gene when the cell that has undergone alteration encodes a known antimicrobial that is altered by the means described in the current invention to obtain a more efficacious antimicrobial. Examples of mismatch repair proteins and nucleic acid sequences include the following: PMS2 (mouse) (SEQ ID NO:7) MEQTEGVSTE CAKAIKPIDG KSVHQICSGQ VILSLSTAVK ELIENSVDAG ATTIDLRLKD 60 YGVDLIEVSD NGCGVEEENF EGLALKHHTS KIQEFADLTQ VETFGFRGEA LSSLCALSDV 120 TISTCHGSAS VGTRLVFDHN GKITQKTPYP RPKGTTVSVQ HLFYTLPVRY KEFQRNIKKE 180 YSKMVQVLQA YCIISAGVRV SCTNQLGQGK RHAWCTSGT SGMKENIGSV FGQKQLQSLI 240 PFVQLPPSDA VCEEYGLSTS GRHKTFSTFR ASFHSARTAP GGVQQTGSFS SSIRGPVTQQ 300 RSLSLSMRFY HMYNRHQYPF WLNVSVDSE CVDINVTPDK RQILLQEEKL LLAVLKTSLI 360 GMFDSDANK NVNQQPL DV EGNLVKLHTA ELEKPVPGKQ DNSPSLKSTA DEKRVASISR 420 LREAFSLHPT KEIKSRGPET AELTRSFPSE KRGVLSSYPS DVISYRG RG SQDKLVSPTD 480 SPGDC DRE IEKDSGLSST SAGSEEEFST PEVASSFSSD YNVSSLEDRP SQETINCGDL 540 DCRPPGTGQS LKPEDHGYQC KA PLARLSP TNAKRFKTEE RPSNVNISQR LPGPQSTSAA 600 EVDVAIKMNK RIVLLEFSLS SLAKRMKQLQ HLKAQNKHEL SYRKFRAKIC PGENQAAEDE 660 LRKEISKSMF AEMEILGQFN LGFIVTKLKE DLFLVDQHAA DEKYNFEMLQ QHTVLQAQRL 720 ITP TLNLTA VNEAVLIENL EIFRKNGFDF VIDEDAPVTE RAKLIS PTS KNWTFGPQDI 780 DELIFMLSDS PGVMCRPSRV RQMFASRACR KSVMIGTALN ASEMKKLITH MGEMDHP NC 840 PHGRPTMRHV ANLDVISQN 859 PMS2 (mouse cDNA) (SEQ ID NO:8) gaattccggt gaaggtcctg aagaatttcc agattcctga gtatcattgg aggagacaga 60 taacctgtcg tcaggtaacg atggtgtata tgcaacagaa atgggtgttc ctggagacgc 120 gtcttttccc gagagcggca ccgcaactct cccgcggtga ctgtgactgg aggagtcctg 180 catccatgga gcaaaccgaa ggcgtgagta cagaatgtgc taaggccatc aagcctattg 240 atgggaagtc agtccatcaa atttgttctg ggcaggtgat actcagttta agcaccgctg 300 tgaaggagtt gatagaaaat agtgtagatg ctggtgctac tactattgat ctaaggctta 360 aagactatgg ggtggacctc attgaagttt cagacaatgg atgtggggta gaagaagaaa 420 actttgaagg tctagctctg aaacatcaca catctaagat tcaagagttt gccgacctca 480 cgcaggttga aactttcggc tttcgggggg aagctctgag ctctctgtgt gcactaagtg 540 atgtcactat atctacctgc cacgggtctg caagcgttgg gactcgactg gtgtttgacc 600 ataatgggaa aatcacccag aaaactccct acccccgacc taaaggaacc acagtcagtg 660 tgcagcactt attttataca ctacccgtgc gttacaaaga gtttcagagg aacattaaaa 720 aggagtattc caaaatggtg caggtcttac aggcgtactg tatcatctca gcaggcgtcc 780 gtgtaagctg cactaatcag ctcggacagg ggaagcggca cgctgtggtg tgcacaagcg 840 gcacgtctgg catgaaggaa aatatcgggt ctgtgtttgg ccagaagcag ttgcaaagcc 900 tcattccttt tgttcagctg ccccctagtg acgctgtgtg tgaagagtac ggcctgagca 960 cttcaggacg ccacaaaacc ttttctacgt ttcgggcttc atttcacagt gcacgcacgg 1020 cgccgggagg agtgcaacag acaggcagtt tttcttcatc aatcagaggc cctgtgaccc 1080 agcaaaggtc tctaagcttg tcaatgaggt tttatcacat gtataaccgg catcagtacc 1140 catttgtcgt ccttaacgtt tccgttgact cagaatgtgt ggatattaat gtaactccag 1200 ataaaaggca aattctacta caagaagaga agctattgct ggccgtttta aagacctcct 1260 tgataggaat gtttgacagt gatgcaaaca agcttaatgt caaccagcag ccactgctag 1320 atgttgaagg taacttagta aagctgcata ctgcagaact agaaaagcct gtgccaggaa 1380 agcaagataa ctctccttca ctgaagagca cagcagacga gaaaagggta gcatccatct 1440 ccaggctgag agaggccttt tctcttcatc ctactaaaga gatcaagtct aggggtccag 1500 agactgctga actgacacgg agttttccaa gtgagaaaag gggcgtgtta tcctcttatc 1560 cttcagacgt catctcttac agaggcctcc gtggctcgca ggacaaattg gtgagtccca 1620 cggacagccc tggtgactgt atggacagag agaaaataga aaaagactca gggctcagca 1680 gcacctcagc tggctctgag gaagagttca gcaccccaga agtggccagt agctttagca 1740 gtgactataa cgtgagctcc ctagaagaca gaccttctca ggaaaccata aactgtggtg 1800 acctggactg ccgtcctcca ggtacaggac agtccttgaa gccagaagac catggatatc 1860 aatgcaaagc tctacctcta gctcgtctgt cacccacaaa tgccaagcgc ttcaagacag 1920 aggaaagacc ctcaaatgtc aacatttctc aaagattgcc tggtcctcag agcacctcag 1980 cagctgaggt cgatgtagcc ataaaaatga ataagagaat cgtgctcctc gagttctctc 2040 tgagttctct agctaagcga atgaagcagt tacagcacct aaaggcgcag aacaaacatg 2100 aactgagtta cagaaaattt agggccaaga tttgccctgg agaaaaccaa gcagcagaag 2160 atgaactcag aaaagagatt agtaaatcga tgtttgcaga gatggagatc ttgggtcagt 2220 ttaacctggg atttatagta accaaactga aagaggacct cttcctggtg gaccagcatg 2280 ctgcggatga gaagtacaac tttgagatgc tgcagcagca cacggtgctc caggcgcaga 2340 ggctcatcac accccagact ctgaacttaa ctgctgtcaa tgaagctgta ctgatagaaa 2400 atctggaaat attcagaaag aatggctttg actttgtcat tgatgaggat gctccagtca 2460 ctgaaagggc taaattgatt tccttaccaa ctagtaaaaa ctggaccttt ggaccccaag 2520 atatagatga actgatcttt atgttaagtg acagccctgg ggtcatgtgc cggccctcac 2580 gagtcagaca gatgtttgct tccagagcct gtcggaagtc agtgatgatt ggaacggcgc 2640 tcaatgcgag cgagatgaag aagctcatca cccacatggg tgagatggac cacccctgga 2700 actgccccca cggcaggcca accatgaggc acgttgccaa tctggatgtc atctctcaga 2760 actgacacac cccttgtagc atagagttta ttacagattg ttcggtttgc aaagagaagg 2820 ttttaagtaa tctgattatc gttgtacaaa aattagcatg ctgctttaat gtactggatc 2880 catttaaaag cagtgttaag gcaggcatga tggagtgttc ctctagctca gctacttggg 2940 tgatccggtg ggagctcatg tgagcccagg actttgagac cactccgagc cacattcatg 3000 agactcaatt caaggacaaa aaaaaaaaga tatttttgaa gccttttaaa aaaaaa 3056 PMS2 (human) (SEQ ID NO:9) ERAESSSTE PAKAIKPIDR KSVHQICSGQ VVLSLSTAVK ELVENSLDAG ATNIDLKLKD 60 YGVDLIEVSD NGCGVEEENF EGLTLKHHTS KIQEFADLTQ VETFGFRGEA LSS CALSDV 120 TISTCHASAK VGTRLMFDHN GKIIQKTPYP RPRGTTVSVQ QLFSTLPVRH KEFQR IKKE 180 YAKMVQVLHA YCIISAGIRV SCTNQLGQGK RQPWCTGGS PSI ENIGSV FGQKQLQSLI 240 PFVQ PPSDS VCEEYGLSCS DALHNLFYIS GFISQCTHGV GRSSTDRQFF FINRRPCDPA 300 KVCRLVNEVY HMYNRHQYPF VVLNISVDSE CVDINVTPDK RQILLQEEKL LLAV KTSLI 360 GMFDSDVNKL NVSQQPLLDV EGNLIKMHAA DLEKP VEKQ DQSPSLRTGE EKKDVSISRL 420 REAFSLRHTT ENKPHSPKTP EPRRSPLGQK RGMLSSSTSG AISDKGVLRP QKEAVSSSHG 480 PSDPTDRAEV EKDSGHGSTS VDSEGFSIPD TGSHCSSEYA ASSPGDRGSQ EHVDSQEKAP 540 ETDDSFSDVD CHSNQEDTGC KFRVLPQPTN LATPNTKRFK KEEILSSSDI CQKLVNTQDM 600 SASQVDVAVK INKKWP DF SMSSLAKRIK QLHHEAQQSE GEQNYRKFRA KICPGENQAA 660 EDELRKEISK T FAEMEIIG QFNLGFIITK LNEDIFIVDQ HATDEKYNFE MLQQHTVLQG 720 QRLIAPQTLN LTAVNEAVLI ENLEIFRK G FDFVIDENAP VTERAKLISL PTSKNWTFGP 780 QDVDELIFML SDSPGVMCRP SRVKQMFASR ACRKSVMIGT ALNTSEM KL ITHMGEMDHP 840 NCPHGRPT RHIANLGVIS QN 862 PMS2 (human cDNA) (SEQ ID NO: 10) cgaggcggat cgggtgttgc atccatggag cgagctgaga gctcgagtac agaacctgct 60 aaggccatca aacctattga tcggaagtca gtccatcaga tttgctctgg gcaggtggta 120 ctgagtctaa gcactgcggt aaaggagtta gtagaaaaca gtctggatgc tggtgccact 180 aatattgatc taaagcttaa ggactatgga gtggatctta ttgaagtttc agacaatgga 240 tgtggggtag aagaagaaaa cttcgaaggc ttaactctga aacatcacac atctaagatt 300 caagagtttg ccgacctaac tcaggttgaa acttttggct ttcgggggga agctctgagc 360 tcactttgtg cactgagcga tgtcaccatt tctacctgcc acgcatcggc gaaggttgga 420 actcgactga tgtttgatca caatgggaaa attatccaga aaacccccta cccccgcccc 480 agagggacca cagtcagcgt gcagcagtta ttttccacac tacctgtgcg ccataaggaa 540 tttcaaagga atattaagaa ggagtatgcc aaaatggtcc aggtcttaca tgcatactgt 600 atcatttcag caggcatccg tgtaagttgc accaatcagc ttggacaagg aaaacgacag 660 cctgtggtat gcacaggtgg aagccccagc ataaaggaaa atatcggctc tgtgtttggg 720 cagaagcagt tgcaaagcct cattcctttt gttcagctgc cccctagtga ctccgtgtgt 780 gaagagtacg gtttgagctg ttcggatgct ctgcataatc ttttttacat ctcaggtttc 840 atttcacaat gcacgcatgg agttggaagg agttcaacag acagacagtt tttctttatc 900 aaccggcggc cttgtgaccc agcaaaggtc tgcagactcg tgaatgaggt ctaccacatg 960 tataatcgac accagtatcc atttgttgtt cttaacattt ctgttgattc agaatgcgtt 1020 gatatcaatg ttactccaga taaaaggcaa attttgctac aagaggaaaa gcttttgttg 1080 gcagttttaa agacctcttt gataggaatg tttgatagtg atgtcaacaa gctaaatgtc 1140 agtcagcagc cactgctgga tgttgaaggt aacttaataa aaatgcatgc agcggatttg 1200 gaaaagccca tggtagaaaa gcaggatcaa tccccttcat taaggactgg agaagaaaaa 1260 aaagacgtgt ccatttccag actgcgagag gccttttctc ttcgtcacac aacagagaac 1320 aagcctcaca gcccaaagac tccagaacca agaaggagcc ctctaggaca gaaaaggggt 1380 atgctgtctt ctagcacttc aggtgccatc tctgacaaag gcgtcctgag acctcagaaa 1440 gaggcagtga gttccagtca cggacccagt gaccctacgg acagagcgga ggtggagaag 1500 gactcggggc acggcagcac ttccgtggat tctgaggggt tcagcatccc agacacgggc 1560 agtcactgca gcagcgagta tgcggccagc tccccagggg acaggggctc gcaggaacat 1620 gtggactctc aggagaaagc gcctgaaact gacgactctt tttcagatgt ggactgccat 1680 tcaaaccagg aagataccgg atgtaaattt cgagttttgc ctcagccaac taatctcgca 1740 accccaaaca caaagcgttt taaaaaagaa gaaattcttt ccagttctga catttgtcaa 1800 aagttagtaa atactcagga catgtcagcc tctcaggttg atgtagctgt gaaaattaat 1860 aagaaagttg tgcccctgga cttttctatg agttctttag ctaaacgaat aaagcagtta 1920 catcatgaag cacagcaaag tgaaggggaa cagaattaca ggaagtttag ggcaaagatt 1980 tgtcctggag aaaatcaagc agccgaagat gaactaagaa aagagataag taaaacgatg 2040 tttgcagaaa tggaaatcat tggtcagttt aacctgggat ttataataac caaactgaat 2100 gaggatatct tcatagtgga ccagcatgcc acggacgaga agtataactt cgagatgctg 2160 cagcagcaca ccgtgctcca ggggcagagg ctcatagcac ctcagactct caacttaact 2220 gctgttaatg aagctgttct gatagaaaat ctggaaatat ttagaaagaa tggctttgat 2280 tttgttatcg atgaaaatgc tccagtcact gaaagggcta aactgatttc cttgccaact 2340 agtaaaaact ggaccttcgg accccaggac gtcgatgaac tgatcttcat gctgagcgac 2400 agccctgggg tcatgtgccg gccttcccga gtcaagcaga tgtttgcctc cagagcctgc 2460 cggaagtcgg tgatgattgg gactgctctt aacacaagcg agatgaagaa actgatcacc 2520 cacatggggg agatggacca cccctggaac tgtccccatg gaaggccaac catgagacac 2580 atcgccaacc tgggtgtcat ttctcagaac tgaccgtagt cactgtatgg aataattggt 2640 tttatcgcag atttttatgt tttgaaagac agagtcttca ctaacctttt ttgttttaaa 2700 atgaaacctg ctacttaaaa aaaatacaca tcacacccat ttaaaagtga tcttgagaac 2760 cttttcaaac c 2771 PMS1 (human) (SEQ ID NO: 11) MKQLPAATVR LLSSSQIITS WSVVKELIE NSLDAGATSV DVKLENYGFD KIEVRDNGEG 60 IKAVDAPV A MKYYTSKINS HEDLENLTTY GFRGEALGSI CCIAEVLITT RTAADNFSTQ 120 YVLDGSGHIL SQKPSHLGQG TTVTALRLFK NLPVRKQFYS TAKKCKDEIK KIQDLLMSFG 180 ILKPDLRIVF VHNKAVI QK SRVSDHKMAL MSVLGTAVMN NMESFQYHSE ESQIYLSGFL 240 PKCDADHSFT SLSTPERSFI FINSRPVHQK DILKLIRHHY NLKCLKESTR LYPVFFLKID 300 VPTADVDVNL TPDKSQVLLQ N ESVLIALE NLMTTCYGPL PSTNSYENNK TDVSAADIVL 360 SKTAETDVLF 'NKVESSGK Y SNVDTSVIPF QNDMHNDESG KNTDDCLNHQ ISIGDFGYGH 420 CSSEISNIDK NTKNAFQDIS MSNVS ENSQ TEYSKTCFIS SVKHTQSENG NKDHIDESGE 480 NEEEAGLENS SEISADE SR GNILKNSVGE NIEPVKILVP EKSLPCKVSN NNYPIPEQMN 540 LNEDSCNKKS NVIDNKSGKV TAYDLLSNRV IKKPMSASAL FVQDHRPQFL IENPKTSLED 600 ATLQIEELWK TLSEEEKLKY EEKATKDLER YNSQMKRAIE QESQMSLKDG RKKIKPTSAW 660 NLAQKHKLKT SLSNQPKLDE LLQSQIEKRR SQNIK VQIP FSMKNLKINF KKQNKVDLEE 720 KDEPCLIHNL RFPDAWLMTS KTEV LLNPY RVEEALLFKR LLENHKLPAE PLEKPI LTE 780 SLFNGSHYLD VLYKMTADDQ RYSGSTYLSD PRLTANGFKI KLI PGVSITE NYLEIEGMAN 840 CLPFYGVADL KEILNAILNR NAKEVYECRP RKVISYLEGE AVRLSRQLPM YLSKEDIQDI 900 IYRMKHQFGN EIKECVHGRP FFHHLTYLPE TT 932 PMS1 (human) (SEQ ID NO:12) ggcacgagtg gctgcttgcg gctagtggat ggtaattgcc tgcctcgcgc tagcagcaag 60 ctgctctgtt aaaagcgaaa atgaaacaat tgcctgcggc aacagttcga ctcctttcaa 120 gttctcagat catcacttcg gtggtcagtg ttgtaaaaga gcttattgaa aactccttgg 180 atgctggtgc cacaagcgta gatgttaaac tggagaacta tggatttgat aaaattgagg 240 tgcgagataa cggggagggt atcaaggctg ttgatgcacc tgtaatggca atgaagtact 300 acacctcaaa aataaatagt catgaagatc ttgaaaattt gacaacttac ggttttcgtg 360 gagaagcctt ggggtcaatt tgttgtatag ctgaggtttt aattacaaca agaacggctg 420 ctgataattt tagcacccag tatgttttag atggcagtgg ccacatactt tctcagaaac 480 cttcacatct tggtcaaggt acaactgtaa ctgctttaag attatttaag aatctacctg 540 taagaaagca gttttactca actgcaaaaa aatgtaaaga tgaaataaaa aagatccaag 600 atctcctcat gagctttggt atccttaaac ctgacttaag gattgtcttt gtacataaca 660 aggcagttat ttggcagaaa agcagagtat cagatcacaa gatggctctc atgtcagttc 720 tggggactgc tgttatgaac aatatggaat cctttcagta ccactctgaa gaatctcaga 780 tttatctcag tggatttctt ccaaagtgtg atgcagacca ctctttcact agtctttcaa 840 caccagaaag aagtttcatc ttcataaaca gtcgaccagt acatcaaaaa gatatcttaa 900 agttaatccg acatcattac aatctgaaat gcctaaagga atctactcgt ttgtatcctg 960 ttttctttct gaaaatcgat gttcctacag ctgatgttga tgtaaattta acaccagata 1020 aaagccaagt attattacaa aataaggaat ctgttttaat tgctcttgaa aatctgatga 1080 cgacttgtta tggaccatta cctagtacaa attcttatga aaataataaa acagatgttt 1140 ccgcagctga catcgttctt agtaaaacag cagaaacaga tgtgcttttt aataaagtgg 1200 aatcatctgg aaagaattat tcaaatgttg atacttcagt cattccattc caaaatgata 1260 tgcataatga tgaatctgga aaaaacactg atgattgttt aaatcaccag ataagtattg 1320 gtgactttgg ttatggtcat tgtagtagtg aaatttctaa cattgataaa aacactaaga 1380 atgcatttca ggacatttca atgagtaatg tatcatggga gaactctcag acggaatata 1440 gtaaaacttg ttttataagt tccgttaagc acacccagtc agaaaatggc aataaagacc 1500 atatagatga gagtggggaa aatgaggaag aagcaggtct tgaaaactct tcggaaattt 1560 ctgcagatga gtggagcagg ggaaatatac ttaaaaattc agtgggagag aatattgaac 1620 ctgtgaaaat tttagtgcct gaaaaaagtt taccatgtaa agtaagtaat aataattatc 1680 caatccctga acaaatgaat cttaatgaag attcatgtaa caaaaaatca aatgtaatag 1740 ataataaatc tggaaaagtt acagcttatg atttacttag caatcgagta atcaagaaac 1800 ccatgtcagc aagtgctctt tttgttcaag atcatcgtcc tcagtttctc atagaaaatc 1860 ctaagactag tttagaggat gcaacactac aaattgaaga actgtggaag acattgagtg 1920 aagaggaaaa actgaaatat gaagagaagg ctactaaaga cttggaacga tacaatagtc 1980 aaatgaagag agccattgaa caggagtcac aaatgtcact aaaagatggc agaaaaaaga 2040 taaaacccac cagcgcatgg aatttggccc agaagcacaa gttaaaaacc tcattatcta 2100 atcaaccaaa acttgatgaa ctccttcagt cccaaattga aaaaagaagg agtcaaaata 2160 ttaaaatggt acagatcccc ttttctatga aaaacttaaa aataaatttt aagaaacaaa 2220 acaaagttga cttagaagag aaggatgaac cttgcttgat ccacaatctc aggtttcctg 2280 atgcatggct aatgacatcc aaaacagagg taatgttatt aaatccatat agagtagaag 2340 aagccctgct atttaaaaga cttcttgaga atcataaact tcctgcagag ccactggaaa 2400 agccaattat gttaacagag agtcttttta atggatctca ttatttagac gttttatata 2460 aaatgacagc agatgaccaa agatacagtg gatcaactta cctgtctgat cctcgtctta 2520 cagcgaatgg tttcaagata aaattgatac caggagtttc aattactgaa aattacttgg 2580 aaatagaagg aatggctaat tgtctcccat tctatggagt agcagattta aaagaaattc 2640 ttaatgctat attaaacaga aatgcaaagg aagtttatga atgtagacct cgcaaagtga 2700 taagttattt agagggagaa gcagtgcgtc tatccagaca attacccatg tacttatcaa 2760 aagaggacat ccaagacatt atctacagaa tgaagcacca gtttggaaat gaaattaaag 2820 agtgtgttca tggtcgccca ttttttcatc atttaaccta tcttccagaa actacatgat 2880 taaatatgtt taagaagatt agttaccatt gaaattggtt ctgtcataaa acagcatgag 2940 tctggtttta aattatcttt gtattatgtg tcacatggtt attttttaaa tgaggattca 3000 ctgacttgtt tttatattga aaaaagttcc acgtattgta gaaaacgtaa ataaactaat 3060 aac 3063 MSH2 (human) (SEQ IDNO:13) MAVQPKETLQ LESAAEVGFV RFFQGMPEKP TTTVRLFDRG DFYTAHGEDA LAAREVFKT 60 QGVIKYMGPA GAKNLQSWL SKMNFESFVK DLLLVRQYRV EVYKNRAGNK ASKENDWYLA 120 Y ASPGNLSQ FEDILFGNND MSASIGWGV KMSAVDGQRQ VGVGYVDSIQ RKLGLCEFPD 180 NDQFSNLEAL LIQIGPKECV LPGGETAGDM GKLRQIIQRG GILITERKKA DFSTKDIYQD 240 LNRLLKGKKG EQMNSAVLPE ENQVAVSSL SAVIKFLELL SDDSNFGQFE LTTFDFSQYM 300 KLDIAAVRAL NLFQGSVEDT TGSQSLAALL NKCKTPQGQR LVNQWIKQPL MDKNRIEERL 360 NLVEAFVEDA ELRQTLQEDL LRRFPDLNRL AKKFQRQAAN LQDCYRLYQG INQLPNVIQA 420 LEKHEGKHQK LLAVFVTPL TDLRSDFSKF QEMIETTLDM DQVENHEFLV KPSFDPNLSE 480 LREIMNDLEK KMQSTLISAA RDLGLDPGKQ IKLDSSAQFG YYFRVTCKEE KVLRNNKNFS 540 TVDIQKNGVK FTNSKLTSLN EEYTKNKTEY EEAQDAIVKE IVNISSGYVE PMQTLNDV A 600 ' QLDAWSFAH VSNGAPVPYV RPAILEKGQG RIILKASRHA CVEVQDEIAF IPNDVYFEKD 660 KQMFHIITGP NMGGKSTYIR QTGVIVLMAQ IGCFVPCESA EVSIVDCILA RVGAGDSQLK 720 GVSTFMAEML ETASILRSAT KDSLIIIDEL GRGTSTYDGF GLAWAISEYI ATKIGAFCMF 780 ATHFHELTAL ANQIPTVNNL HVTALTTEET LTMLYQVKKG VCDQSFGIHV AELANFPKHV 840 IECAKQKALE LEEFQYIGES QGYDIMEPAA KCYLEREQG EKIIQEFLSK VKQMPFTEMS 900 EENITIKLKQ LKAEVIAKNN SFVNEIISRI KVTT 934 MSH2 (human cDNA) (SEQ ID NO: 14) ggcgggaaac agcttagtgg gtgtggggtc gcgcattttc ttcaaccagg aggtgaggag 60 gtttcgacat ggcggtgcag ccgaaggaga cgctgcagtt ggagagcgcg gccgaggtcg 120 gcttcgtgcg cttctttcag ggcatgccgg agaagccgac caccacagtg cgccttttcg 180 accggggcga cttctatacg gcgcacggcg aggacgcgct gctggccgcc cgggaggtgt 240 tcaagaccca gggggtgatc aagtacatgg ggccggcagg agcaaagaat ctgcagagtg 300 ttgtgcttag taaaatgaat tttgaatctt ttgtaaaaga tcttcttctg gttcgtcagt 360 atagagttga agtttataag aatagagctg gaaataaggc atccaaggag aatgattggt 420 atttggcata taaggcttct cctggcaatc tctctcagtt tgaagacatt ctctttggta 480 acaatgatat gtcagcttcc attggtgttg tgggtgttaa aatgtccgca gttgatggcc 540 agagacaggt tggagttggg tatgtggatt ccatacagag gaaactagga ctgtgtgaat 600 tccctgataa tgatcagttc tccaatcttg aggctctcct catccagatt ggaccaaagg 660 aatgtgtttt acccggagga gagactgctg gagacatggg gaaactgaga cagataattc 720 aaagaggagg aattctgatc acagaaagaa aaaaagctga cttttccaca aaagacattt 780 atcaggacct caaccggttg ttgaaaggca aaaagggaga gcagatgaat agtgctgtat 840 tgccagaaat ggagaatcag gttgcagttt catcactgtc tgcggtaatc aagtttttag 900 aactcttatc agatgattcc aactttggac agtttgaact gactactttt gacttcagcc 960 agtatatgaa attggatatt gcagcagtca gagcccttaa cctttttcag ggttctgttg 1020 aagataccac tggctctcag tctctggctg ccttgctgaa taagtgtaaa acccctcaag 1080 gacaaagact tgttaaccag tggattaagc agcctctcat ggataagaac agaatagagg 1140 agagattgaa tttagtggaa gcttttgtag aagatgcaga attgaggcag actttacaag 1200 aagatttact tcgtcgattc ccagatctta accgacttgc caagaagttt caaagacaag 1260 cagcaaactt acaagattgt taccgactct atcagggtat aaatcaacta ' cctaatgtta 1320 tacaggctct ggaaaaacat gaaggaaaac accagaaatt attgttggca gtttttgtga 1380 ctcctcttac tgatcttcgt tctgacttct ccaagtttca ggaaatgata gaaacaactt 1440 tagatatgga tcaggtggaa aaccatgaat tccttgtaaa accttcattt gatcctaatc 1500 tcagtgaatt aagagaaata atgaatgact tggaaaagaa gatgcagtca acattaataa 1560 gtgcagccag agatcttggc ttggaccctg gcaaacagat taaactggat tccagtgcac 1620 agtttggata ttactttcgt gtaacctgta aggaagaaaa agtccttcgt aacaataaaa 1680 actttagtac tgtagatatc cagaagaatg gtgttaaatt taccaacagc aaattgactt 1740 ctttaaatga agagtatacc aaaaataaaa cagaatatga agaagcccag gatgccattg 1800 ttaaagaaat tgtcaatatt tcttcaggct atgtagaacc aatgcagaca ctcaatgatg 1860 tgttagctca gctagatgct gttgtcagct ttgctcacgt gtcaaatgga gcacctgttc 1920 catatgtacg accagccatt ttggagaaag gacaaggaag aattatatta aaagcatcca 1980 ggcatgcttg tgttgaagtt caagatgaaa ttgcatttat tcctaatgac gtatactttg 2040 aaaaagataa acagatgttc cacatcatta ctggccccaa tatgggaggt aaatcaacat 2100 atattcgaca aactggggtg atagtactca tggcccaaat tgggtgtttt gtgccatgtg 2160 agtcagcaga agtgtccatt gtggactgca tcttagcccg agtaggggct ggtgacagtc 2220 aattgaaagg agtctccacg ttcatggctg aaatgttgga aactgcttct atcctcaggt 2280 ctgcaaccaa agattcatta ataatcatag atgaattggg aagaggaact tctacctacg 2340 atggatttgg gttagcatgg gctatatcag aatacattgc aacaaagatt ggtgcttttt 2400 gcatgtttgc aacccatttt catgaactta ctgccttggc caatcagata ccaactgtta 2460 ataatctaca tgtcacagca ctcaccactg aagagacctt aactatgctt tatcaggtga 2520 agaaaggtgt ctgtgatcaa agttttggga ttcatgttgc agagcttgct aatttcccta 2580 agcatgtaat agagtgtgct aaacagaaag ccctggaact tgaggagttt cagtatattg 2640 gagaatcgca aggatatgat atcatggaac cagcagcaaa gaagtgctat ctggaaagag 2700 agcaaggtga aaaaattatt caggagttcc tgtccaaggt gaaacaaatg ccctttactg 2760 aaatgtcaga agaaaacatc acaataaagt taaaacagct aaaagctgaa gtaatagcaa 2820 agaataatag ctttgtaaat gaaatcattt cacgaataaa agttactacg tgaaaaatcc 2880 cagtaatgga atgaaggtaa tattgataag ctattgtctg taatagtttt atattgtttt 2940 atattaaccc tttttccata gtgttaactg tcagtgccca tgggctatca acttaataag 3000 atatttagta atattttact ttgaggacat tttcaaagat ttttattttg aaaaatgaga 3060 gctgtaactg aggactgttt gcaattgaca taggcaataa taagtgatgt gctgaatttt 3120 ataaataaaa tcatgtagtt tgtgg 3145 MLHl (human) (SEQ ID NO: 15) MSFVAGVIRR LDETVVNRIA AGEVIQRPAN AIKE IENCL DAKSTSIQVI VKEGGLKLIQ 60 IQDNGTGIRK EDLDIVCERF TTSKLQSFED LASISTYGFR GEALASISHV AHVTITTKTA 120 DGKCAYRASY SDGKLKAPPK PCAGNQGTQI TVEDLFYNIA TRRKALKNPS EEYGKILEVV 180 GRYSVHNAGI SFSVKKQGET VADVRTLPNA STVDNIRSIF GNAVSRELIE IGCEDKTLAF 240 KMNGYISNAN YSVKKCIFLL FINHR VEST SLRKAIETVY AAYLPKNTHP FLY SLEISP 300 QNVDVNVHPT KHEVHFLHEE SILERVQQHI ESKL GSNSS RMYFTQTLLP GLAGPSGE V 360 KSTTSLTSSS TSGSSDKVYA HQMVRTDSRE QKLDAFLQPL SKPLSSQPQA IVTEDKTDIS 420 SGRARQQDEE MLELPAPAEV AAKNQSLEGD TTKGTSEMSE KRGPTSSNPR KRHREDSDVE 480 MVEDDSRKEM TAACTPRRRI INLTSVLSLQ EEINEQGHEV LREMLHNHSF VGCVNPQWAL 540 AQHQTKLYLL NTTKLSEELF YQILIYDFAN FGVLR SEPA PLFDLAMLAL DSPESG TEE 600 DGPKEGLAEY IVEFLKKKAE MLADYFSLEI DEEGNLIGLP LLIDNYVPPL EGLPIFILRL 660 ATEVNWDEEK ECFESLSKEC AMFYSIR QY ISEESTLSGQ QSEVPGSIPN SWKWTVEHIV 720 YKALRSHILP PKHFTEDGNI LQLANLPDLY KVFERC 756 MLHl (human) (SEQ ID NO: 16) cttggctctt ctggcgccaa aatgtcgttc gtggcagggg ttattcggcg gctggacgag 60 acagtggtga accgcatcgc ggcgggggaa gttatccagc ggccagctaa tgctatcaaa 120 gagatgattg agaactgttt agatgcaaaa tccacaagta ttcaagtgat tgttaaagag 180 ggaggcctga agttgattca gatccaagac aatggcaccg ggatcaggaa agaagatctg 240 gatattgtat gtgaaaggtt cactactagt aaactgcagt cctttgagga tttagccagt 300 atttctacct atggctttcg aggtgaggct ttggccagca taagccatgt ggctcatgtt 360 actattacaa cgaaaacagc tgatggaaag tgtgcataca gagcaagtta ctcagatgga 420 aaactgaaag cccctcctaa accatgtgct ggcaatcaag ggacccagat cacggtggag 480 gacctttttt acaacatagc cacgaggaga aaagctttaa aaaatccaag tgaagaatat 540 gggaaaattt tggaagttgt tggcaggtat tcagtacaca atgcaggcat tagtttctca 600 gttaaaaaac aaggagagac agtagctgat gttaggacac tacccaatgc ctcaaccgtg 660 gacaatattc gctccatctt tggaaatgct gttagtcgag aactgataga aattggatgt 720 gaggataaaa ccctagcctt caaaatgaat ggttacatat ccaatgcaaa ctactcagtg 780 aagaagtgca tcttcttact cttcatcaac catcgtctgg tagaatcaac ttccttgaga 840 aaagccatag aaacagtgta tgcagcctat ttgcccaaaa acacacaccc attcctgtac 900 ctcagtttag aaatcagtcc ccagaatgtg gatgttaatg tgcaccccac aaagcatgaa 960 gttcacttcc tgcacgagga gagcatcctg gagcgggtgc agcagcacat cgagagcaag 1020 ctcctgggct ccaattcctc caggatgtac ttcacccaga ctttgctacc aggacttgct 1080 ggcccctctg gggagatggt taaatccaca acaagtctga cctcgtcttc tacttctgga 1140 agtagtgata aggtctatgc ccaccagatg gttcgtacag attcccggga acagaagctt 1200 gatgcatttc tgcagcctct gagcaaaccc ctgtccagtc agccccaggc cattgtcaca 1260 gaggataaga cagatatttc tagtggcagg gctaggcagc aagatgagga gatgcttgaa 1320 ctcccagccc ctgctgaagt ggctgccaaa aatcagagct tggaggggga tacaacaaag 1380 gggacttcag aaatgtcaga gaagagagga cctacttcca gcaaccccag aaagagacat 1440 cgggaagatt ctgatgtgga aatggtggaa gatgattccc gaaaggaaat gactgcagct 1500 tgtacccccc ggagaaggat cattaacctc actagtgttt tgagtctcca ggaagaaatt 1560 aatgagcagg gacatgaggt tctccgggag atgttgcata accactcctt cgtgggctgt 1620 gtgaatcctc agtgggcctt ggcacagcat caaaccaagt tataccttct caacaccacc 1680 aagcttagtg aagaactgtt ctaccagata ctcatttatg attttgccaa ttttggtgtt 1740 ctcaggttat cggagccagc accgctcttt gaccttgcca tgcttgcctt agatagtcca 1800 gagagtggct ggacagagga agatggtccc aaagaaggac ttgctgaata cattgttgag 1860 tttctgaaga agaaggctga gatgcttgca gactatttct ctttggaaat tgatgaggaa 1920 gggaacctga ttggattacc ccttctgatt gacaactatg tgcccccttt ggagggactg 1980 cctatcttca ttcttcgact agccactgag gtgaattggg acgaagaaaa ggaatgtttt 2040 gaaagcctca gtaaagaatg cgctatgttc tattccatcc ggaagcagta catatctgag 2100 gagtcgaccc tctcaggcca gcagagtgaa gtgcctggct ccattccaaa ctcctggaag 2160 tggactgtgg aacacattgt ctataaagcc ttgcgctcac acattctgcc tcctaaacat 2220 ttcacagaag atggaaatat cctgcagctt gctaacctgc ctgatctata caaagtcttt 2280 gagaggtgtt aaatatggtt atttatgcac tgtgggatgt gttcttcttt ctctgtattc 2340 cgatacaaag tgttgtatca aagtgtgata tacaaagtgt accaacataa gtgttggtag 2400 cacttaagac ttatacttgc cttctgatag tattccttta tacacagtgg attgattata 2460 aataaataga tgtgtcttaa cata 2484 hPMS2-134 (human) (SEQ ID NO:17) MERAESSSTE PAKAIKPIDR KSVHQICSGQ VVLSLSTAVK E VENSLDAG ATNIDLKLKD 60 YGVDLIEVSD NGCGVEEENF EGLTLKHHTS KIQEFADLTQ VETFGFRGEA LSSLCALSDV 120 TISTCHASAK VGT 133 hPMS2-134 (human cDNA) (SEQ ID NO: 18) cgaggcggat cgggtgttgc atccatggag cgagctgaga gctcgagtac agaacctgct 60 aaggccatca aacctattga tcggaagtca gtccatcaga tttgctctgg gcaggtggta 120 ctgagtctaa gcactgcggt aaaggagtta gtagaaaaca gtctggatgc tggtgccact 180 aatattgatc taaagcttaa ggactatgga gtggatctta ttgaagtttc agacaatgga 240 tgtggggtag aagaagaaaa cttcgaaggc ttaactctga aacatcacac atctaagatt 300 caagagtttg ccgacctaac tcaggttgaa acttttggct ttcgggggga agctctgagc 360 tcactttgtg cactgagcga tgtcaccatt tctacctgcc acgcatcggc gaaggttgga 420 acttga 426 The above disclosure generally describes the present invention. A more complete understanding can be obtained by reference to the following specific examples, which are provided herein for purposes of illustration only, and are not intended to limit the scope of the invention. EXAMPLES Example 1: hPMS2-134 Encodes a Dominant Negative Mismatch Repair Protein A profound defect in MMR was found in the normal cells of two HNPCC patients. That this defect was operative in vivo was demonstrated by the widespread presence of microsatellite instability in non-neoplastic cells of such patients. One ofthe two patients had a germ-line truncating mutation ofthe hPMS2 gene at codon 134 (the hPMS2-134 mutation), while the other patient had a small germ-line deletion within the hMLHl gene. Leach et al, Cell, 1993, 75, 1215-1225. These data contradicted the two-hit model generally believed to explain the biochemical and biological features of HNPCC patients. The basis for this MMR deficiency in the normal cells of these patients was unclear, and several potential explanations were offered. For example, it was possible that the second allele ofthe relevant MMR gene was inactivated in the germ-line of these patients through an undiscovered mechanism, or that unknown mutations of other genes involved in the MMR process were present that cooperated with the known germ-line mutation. It is clear from knock-out experiments in mice that MMR-deficiency is compatible with normal growth and development, supporting these possibilities. Edehnann et al, Cell, 1996, 85, 1125-1134. Alternatively, it was possible that the mutant alleles exerted a dominant-negative effect, resulting in MMR deficiency even in the presence of the wild-type allele ofthe corresponding MMR gene and all other genes involved in the MMR process. To distinguish between these possibilities, the truncated polypeptide encoded by the hPMS2-134 mutation was expressed in an MMR proficient cell line its affect on MMR activity was analyzed. The results showed that this mutant could indeed exert a dominant-negative effect, resulting in biochemical and genetic manifestations of MMR deficiency. One embodiment ofthe present invention is demonstrated in Table 1, where a Syrian hamster fibroblast cell line (TK) was transfected with an expression vector containing the hPMS2-134 (TK-PMS2-134) or the empty expression vector (TKvect), which also contains the NEO gene as a selectable marker. TK-PMS2-134 cells were determined to be stably expressing the gene via western blot analysis (data not shown). Nuclear lysates from hPMS2-134 and control cells were measured for the ability to correct mismatched DNA substrates. As shown in Table 1, TK-PMS2-134 cells had a dramatic decrease in repair activity while TKvect control cells were able to repair mismatched DNA duplexes at a rate of ~4.0 fmol/15 minutes (p<.01). Table 1: Relative endogenous MMR activity of MMR-proficient cells expressing an ectopically expressed morphogene or an empty expression vector Cell Lines 5' DNA Repair activity of G/T mismatch (fmol/15 minutes) TKvect 1 3.5 2 2.9 3 5.5 TK-PMS2-134 1 0 2 0 3 0.5 These data show that the expression ofthe TK-PMS2-134 results in suppressed MMR of a host organism and allows for an enhanced mutation rate of genetic loci with each mitosis. Example 2: hPMS2-134 Can Alter Genes In Vivo An example ofthe ability to alter mismatch repair comes from experiments using manipulation of mismatch repair TK cells (described above) that expressed the TK- hPMS2-134 mutant were used by transfection ofthe mammalian expression construct containing a defective β-galactosidase gene (referred to as pCAR-OF) which was transfected into TK-hPMS2-134 or TKvect cells as described above. The pCAR-OF vector consists of a β-galactosidase gene containing a 29-basepair poly-CA tract inserted at the 5' end of its coding region, which causes the wild-type reading frame to shift out-of-frame. This chimeric gene is cloned into the pCEP4, which contains the constitutively active cytomegalovirus (CMV) promoter upstream ofthe cloning site and also contains the hygromycin-resistance gene that allows for selection of cells containing this vector. The pCAR-OF reporter cannot generate β-galactosidase activity unless a frame-restoring mutation (t.e., insertion or deletion) arises following transfection into a host. Another reporter vector called pCAR-IF contains a β-galactosidase in which a 27-bp poly-CA repeat was cloned into the same site as the pCAR-OF gene, but it is biologically active because the removal of a single repeat restores the open reading frame and produces a functional chimeric β-galactosidase polypeptide (not shown). In these experiments, TK- hPMS2-134 and TKvect cells were transfected with the pCAR-OF reporter vector and selected for 17 days in neomycin plus hygromycin selection medium. After the 17 days, resistant colonies were stained for β-galactosidase production to determine the number of clones containing a genetically altered β-galactosidase gene. All conditions produced a relatively equal number of neomycin/hygromycin resistant cells, however, only the cells expressing the TK-hPMS2-134 contained a subset of clones that were positive for β- galactosidase activity. Representative results are shown in Table 2, which shows the data from these experiments where cell colonies were stained in situ for β-galactosidase activity and scored for activity. Cells were scored positive if the colonies turned blue in the presence of X-gal substrate and scored negative if colonies remained white. Analysis of triplicate experiments showed that a significant increase in the number of functional β- galactosidase positive cells was found in the TK-hPMS2-134 cultures, while no β- galactosidase positive cells were seen in the control TKvect cells. Table 2. Number of TKmorph and TKvect cells containing functional β-galactosidase activity Cells White Colonies Blue Colonies % Clones with altered B-gal Tkvect 65 +/- 9 0 0/65 = 0% TK-PMS2-134 40 +/- 12 28 +/- 4 28/68 = 41% TK-PMS2-134/pCAR-OF clones that were pooled and expanded also showed a number of cells that contained a functional β-galactosidase gene. No β-galactosidase positive cells were observed in TKvect cells transfected with the pCAR-OF vector. These data are shown in Figure 1 where the dark staining in panel B represent β-galactosidase positive cells present in the TK-PMS2- 134/ρCAR-OF cultures while none are found in the TKvect cells grown under similar conditions (panel A). These data demonstrate the ability of he mutant mismatch repair gene, hPMS2-134, to generate gene alterations in vivo, which allows for the rapid screening of clones with altered polypeptides exhibiting new biochemical features. To confirm that alterations within the nucleotide sequences ofthe β-galactosidase gene was indeed responsible for the in vivo β-galactosidase activity present in TK-hPMS2- 134 clones, RNA was isolated from TK-hPMS2-134/pCAR-OF and TKvect/pCAR-OF and the β-galactosidase mRNA primary structure was examined by reverse transcriptase polymerase chain reaction (RT-PCR) amplification and sequencing. Sequence analysis of β-galactosidase message from TKvect cells found no structural alterations in the input gene sequence. Analysis ofthe β-galactosidase message from TK-hPMS-134 cells found several changes within the coding sequences ofthe gene. These sequence alterations included insertion and deletions ofthe poly CA tract in the amino terminus as expected. Other alterations included insertions of sequences outside ofthe polyCA repeat as well as a series of single base alterations contained throughout the length ofthe gene. A summary ofthe genetic alterations are given in Figure 2 where a schematic representation ofthe β-galactosidase gene is shown with the regions and types of genetic alterations depicted below. Plasmids. The full-length wild-type hPMS2 cDNA was obtained from a human Hela cDNA library as described in Strand et. al. , Nature, 1993, 365, 274-276, which is incorporated herein by reference in its entirety. An hPMS2 cDNA containing a termination codon at amino acid 134 was obtained via RT-PCR from the patient in which the mutation was discovered. Nicolaides et. al , Mol. Cell. Biol , 1998, 18, 1635-1641, which is incorporated herein by reference in its entirety. The cDNA fragments were cloned into the BamHI site into the pSG5 vector, which contains an SV40 promoter followed by an SV40 polyadenylation signal. Nicolaides et al. , Genomics, 1995, 29, 329-334, which is incorporated herein by reference in its entirety. The pCAR reporter vectors described in Figure 1 were constructed as described in Palombo et al. , Nature, 1994, 36, 417, which is incorporated herein by reference in its entirety. β-galactosidase assay. Seventeen days following transfection with pCAR, β-galactosidase assays were performed using 20 μg of protein in 45 mM 2-mercaptoethanol, 1 mM MgCl 2 , 0.1 M NaPO 4 and 0.6 mg/ml Chlorophenol red-β-D-galatopyranoside (CPRG, Boehringer Mannheim). Reactions were incubated for 1 hour, terminated by the addition of 0.5 M Na 2 CO 3 , and analyzed by spectrophotometry at 576 nm. Nicolaides et. al , Mol. Cell. Biol , 1998, 18, 1635-1641. For in situ β-galactosidase staining, cells were fixed in 1 % glutaraldehyde in PBS and incubated in 0.15 M NaCl, 1 mM MgCl 2 , 3.3 mM K 4 Fe(CN) 6 , 3.3 mM K 3 Fe(CN) 6 , 0.2% X-Gal for 2 hours at 37°C. Example 3: hPMS2-134 Causes a Defect in MMR Activity The differences in β-galactosidase activity between PMS2-WT and PMS2-134 transfected cells can be due to the PMS2-134 protein disturbing MMR activity resulting in a higher frequency of mutation within the pCAR-OF reporter and re-establishing the ORF. To directly test whether MMR was altered, a biochemical assay for MMR with the individual clones described in Example 1 was employed. Nuclear extracts were prepared from the clones and incubated with heteroduplex substrates containing either a /CA\ insertion-deletion or a G/T mismatch under conditions described previously. The /CA\ and G/T heteroduplexes were used to test repair from the 3' and 5' directions, respectively. There was a dramatic difference between the PMS2-134 expressing clones and the other clones in these assays (Table 3). Table 3. MMR activity of nuclear extracts from SH clones or pooled cultures- Amt of repaired substrate (fmol/15 min) Cell line 37CA\ 3' G/T 5' G/T 37CTGΛ 57CTGΛ SH clones^ PMS2-NOT Clone A 10.2 3.5 Clone B 12.7 2.9 Clone C 13.5 5.5 PMS2-WT Clone A 2.8 2.2 Clone B 5.7 4.8 Clone c 4.7 2.9 PMS2-134 Clone A 2.5 0.0 Clone B 2.4 0.0 Clone C 5.0 0.5 Pooled cultures PMS2-NOT 2.07 ± 0.09 2.37 ± 0.37 3.45 ± 1.35 2.77 ± 1.37 PMS2-WT 1.65 ± 0.94 1.86 ± 0.57 1.13 ± 0.23 1.23 ± 0.65 PMS2-134 0.14 ± 0.2 0.0 ± 0.0 1.31 ± 0.66 0.0 ± 0.0 a The extracts were tested for MMR activity with 24 fmol of heteroduplex. b These data represent similar results derived from more than five independent experiments. While all clones repaired substrates from the 3' direction (/CA\ heteroduplex), cells expressing the PMS2-134 polypeptide had very little 5' repair activity. A similar directional defect in mismatch repair was evident with pooled clones resulting from PMS2-134 transfection, or when the heteroduplex contained a 2-4 base pair loop, examples of which are shown in Table 3. A small decrease in MMR activity was observed in the 3' /CA\ PMS2-WT repair assays, perhaps a result of interference in the biochemical assays by over-expression ofthe PMS2 protein. No significant activity was caused by PMS2-WT 'in the in situ β-galactosidase assays, a result more likely to reflect the in vivo condition. Biochemical assays for mismatch repair. MMR activity in nuclear extracts was performed as described, using 24 fmol of substrate, inBronner et. al, Nature, 1994, 368, 258-261 and Nicolaides et. al., Mol Cell. Biol, 1998, 18, 1635-1641, each of which is incorporated herein by reference in its entirety. Complementation assays were done by adding ~ 100 ng of purified MutLα or MutSα components to 100 μg of nuclear extract, adjusting the final KCl concentration to 100 mM. Bevins, Ciba Found. Symp., 1994, 186, 250-69 and Alderson et al, Res. Microbiol, 1993, 144, 665-72. The substrates used in these experiments contain a strand break 181 nucleotides 5' or 125 nucleotides 3' to the mismatch. Values represent experiments performed at least in duplicate. Example 4: C-Terminus of hPMS2 Mediates Interaction Between hPMS2 and hMLHl To elucidate the mechanism by which hPMS2-134 affected MMR, the interaction between hPMS2 and hMLHl was analyzed. Previous studies have shown that these two proteins dimerize to form a functionally active complex. Bronner et. al. , Nature, 1994, 368, 258-261. Proteins were synthesized in vitro using reticulocyte lysates, employing RNA generated from cloned templates. The full-length hMLHl and hPMS2 proteins bound to each other and were co-precipitated with antibodies to either protein, as expected (data not shown). To determine the domain of hPMS2 that bound to hMLHl, the amino terminus (codons 1-134), containing the most highly conserved domain among mutL proteins (Su et al. , J. Biol. Chem. , 1988, 263, 6829-6835 and Edehnann et al. , Cell, 1996, 85, 1125-1134), and the carboxyl terminus (codons 135-862) were separately cloned and proteins produced in vitro in coupled transcription-translation reactions. Figures 3 A, 3B, and 3C show a representative immunoprecipitation of in v/tro-translated hPMS2 and hMLHl proteins. Figure 3A shows labeled (indicated by an asterisk) or unlabelled proteins incubated with an antibody to the C-terminus of hPMS2 in lanes 1 to 3 and to hMLHl in lanes 4 to 6. Lane 7 contains a nonprogrammed reticulocyte lysate. PMS2-135 contains codons 135 to 862 of hPMS2. The major translation products of hPMS2 and hMLHl are indicated. Figure 3B shows labeled hPMS2-134 (containing codons 1-134 of hPMS2) incubated in the presence or absence of unlabelled hMLHl plus an antibody to hMLHl (lanes 1 and 2, respectively). Lane 3 contains lysate from a nonprogrammed reticulolysate. Figure 3C shows labeled proteins incubated with an antibody to the N terminus of hPMS2. Lane 6 contains a nonprogrammed reticulocyte lysate. In both panels A and B, autoradiographs of immunoprecipitated products are shown. When a 35 S-labelled, full-length hMLHl protein (Figure 3 A, lane 5) was mixed with the unlabelled carboxyl terminal hPMS2 polypeptide, a monoclonal antibody (mAb) to the carboxyl terminus of hPMS2 efficiently immunoprecipitated the labeled hMLHl protein (lane 1). No hMLHl protein was precipitated in the absence of hPMS2 (lane 2). Conversely, when the 35 S-labelled carboxyl-terminus of hPMS2 (lane 3) was incubated with unlabelled, full-length hMLHl protein, an anti-hMLHl mAb precipitated the hPMS2 polypeptide (lane 4). In the absence ofthe unlabelled hMLHl protein, no hPMS2 protein was precipitated by this mAb (lane 6). The same antibody failed to immunoprecipitate the amino-terminus of hPMS2 (amino acids 1-134) when mixed with unlabelled MLHl protein (Figure 3B, lane 1). This finding was corroborated by the converse experiment in which radiolabelled hPMS2-134 (Figure 3C, lane 1) was unable to coprecipitate radiolabelled MLHl when precipitations were done using an N-terminal hPMS2 antibody (Figure 3C, lane 2) while this antibody was shown to be able to coprecipitate MLHl when mixed with wild-type hPMS2 (Figure 3C, lane 4). The initial steps of MMR are dependent on two protein complexes, called MutSα and MutLα. Drummond et. al , Science, 1995, 268, 1909-1912. As the amino terminus of hPMS2 did not mediate binding of hPMS2 to hMLHl, it was of interest to determine whether it might instead mediate the interaction between the MutLα complex (comprised of hMLHl and hPMS2) and the MutSα complex (comprised of MSH2 and GTBP). Because previous studies have demonstrated that MSH2 and the MutLα components do not associate in solution, direct hPMS2-134:MutSα interaction was unable to be assayed. A different approach was used to address this issue, and attempted to complement nuclear extracts from the various SH cell lines with MutSα or MutLα. If the truncated protein present in the PMS2-134 expressing SH cells was binding to MutSα and lowering its effective concentration in the extract, then adding intact MutSα should rescue the MMR defect in such extracts. Figure 4 shows complementation of MMR activity in transduced SH cells. Lysates from pooled clones stably transduced with PMS2-NOT, PMS2-WT, or PMS2-134 were complemented with purified MutSα or MutLα MMR components by using the 5' G/T heteroduplex substrate. The values are presented as the percentage of repair activity in each case compared to that in lysates complemented with both purified MutLα and MutSα components to normalize for repair efficiency in the different lysate backgrounds. The values shown represent the average of at least three different determinations. Purified MutSα added to such extracts had no effect (Figure 4). In contrast, addition of intact MutLα to the extract completely restored directional repair to the extracts from PMS2-134 cells (Figure 4). The results described above lead to several conclusions. First, expression ofthe amino-terminus of hPMS2 results in an increase in microsatellite instability, consistent with a replication error (RER) phenotype. That this elevated microsatellite instability is due to MMR deficiency was proven by evaluation of extracts from stably transduced cells. Interestingly, the expression of PMS2-134 resulted in a polar defect in MMR, which was only observed using heteroduplexes designed to test repair from the 5' direction (no significant defect in repair from the 3' direction was observed in the same extracts). Interestingly, cells deficient in hMLHl also have a polar defect in MMR, but in this case preferentially affecting repair from the 3' direction. Huttner et al, Pediatr. Res., 1999, 45, 785-94. It is known from previous studies in both prokaryotes and eukaryotes that the separate enzymatic components mediate repair from the two different directions. Our results indicate a model in which 5' repair is primarily dependent on hPMS2 while 3' repair is primarily dependent on hMLHl. It is easy to envision how the dimeric complex between PMS2 and MLHl might set up this directionality. The combined results also demonstrate that a defect in directional MMR is sufficient to produce a RER+ phenotype. The dominant-negative function ofthe PMS2-134 polypeptide can result from its binding to MLHl and consequent inhibition of MutLα function. This is based in part on the fact that the most highly conserved domain ofthe PMS2 gene is located in its amino terminus, and the only known biochemical partner for PMS2 is MLHl . The binding studies revealed, however, that the carboxyl terminus- of PMS2, rather than the highly conserved amino terminus, actually mediated binding to MLHl . This result is consistent with those recently obtained in S. cerevisciae, in which the MLHl -interacting domain of PMS1 (the yeast homolog of human PMS2) was localized to its carboxyl-terminus. Leach et al , Cell, 1993, 75, 1215-1225. The add-back experiments additionally showed that the hPMS2-134 mutant was not likely to mediate an interaction with the MutSα complex (Figure 4). The hPMS2-134 polypeptide does not inhibit the initial steps in MMR, but rather interacts with and inhibits a downstream component ofthe pathway, perhaps a nuclease required for repair from the 5' direction. The demonstration that the hPMS2-l 34 mutation can confer a dominant-negative MMR defect to transfected cells helps to explain the phenotype ofthe kindred in which this mutant was discovered. Three individuals from this kindred were found to carry the mutation, a father and his two children. Both children exhibited microsatellite instability in their normal tissues and both developed tumors at an early age, while the father had no evidence of microsatellite instability in his normal cells and was completely healthy at age 35. The only difference known to us with respect to the MMR genes in this family is that the father's mutant allele was expressed at lower levels than the wild-type allele as assessed by sequencing of RT-PCR products of RNA from lymphocytes. The children expressed both alleles at approximately equal levels. The dominant negative attribute of the hPMS2-134 mutant may only be manifest when it is present at sufficient concentrations (at least equimolar) thus, explaining the absence of MMR deficiency in the father. The reason for the differential expression ofthe hPMS2-134 allele in this kindred is not clear, though imprinting is a possibility. Ascertainment of additional, larger kindreds with such mutations will facilitate the investigation of this issue. Western blots. Equal number of cells were lysed directly in lysis buffer (60 mM Tris, pH 6.8, 2% SDS, 10% glycerol, 0.1 M 2-mercaptoethanol, 0.001% bromophenol blue) and boiled for 5 minutes. Lysate proteins were separated by electrophoresis on 4-12% Tris-glycine gels (for analysis of full-length hPMS2) or 4-20% Tris-glycine gels (for analysis of hPMS2-134). Gels were electroblotted onto Immobilon-P (Millipore) in 48 mM Tris base, 40 mM glycine, 0.0375% SDS, 20% methanol and blocked overnight at 4°C in Tris-buffered saline plus 0.05% Tween-20 and 5% condensed milk. Filters were probed with a polyclonal antibody generated against residues 2-20 of hPMS2 (Santa Cruz Biotechnology, Inc.) and a horseradish peroxidase conjugated goat anti-rabbit secondary antibody, using chemiluminescence for detection (Pierce). In vitro translation. Linear DNA fragments containing hPMS2 and hMLHl cDNA sequences were prepared by PCR, incorporating sequences for in vitro transcription and translation in the sense primer. A full-length hMLHl fragment was prepared using the sense primer 5 ' -ggatcctaatacgactcactatagggaga ccaccatgtcgttcgtggcaggg-3 ' (SEQ ID NO : 1 ) (codons 1-6) and the antisense primer 5'-taagtcttaagtgctaccaac-3' (SEQ ID NO:2) (located in the 3' untranslated region, nt 2411-2433), using a wild-type hMLHl cDNA clone as template. A full-length hPMS2 fragment was prepared with the sense primer 5 ' -ggatcctaatacgactcactatagggag accaccatggaacaattgcctgcgg-3' (SEQ ID NO: 3) (codons 1- 6) and the antisense primer 5'-aggttagtgaagactctgtc-3' (SEQ ID NO: 4) (located in 3' untranslated region, nt 2670-2690) using a cloned hPMS2 cDNA as template. A fragment encoding the amino-terminal 134 amino acids of hPMS2 was prepared using the same sense primer and the antisense primer 5'-agtcgagttccaaccttcg-3' (SEQ ID NO:5). A fragment containing codons 135-862 of hPMS135 was generated using the sense primer 5 ' -ggatcctaatacgactcactatagggagaccaccatgatgtttgatcacaat gg-3' (SEQ ID NO:6) (codons 135-141) and the same antisense primer as that used for the full-length hPMS2 protein. These fragments were used to produce proteins via the coupled transcription-translation system (Promega). The reactions were supplemented with 35 S-labelled methionine or unlabelled methionine, as indicated in the text. The PMS135 and hMLHl proteins could not be simultaneously radiolabelled and immunoprecipitated because of their similar molecular weights precluded resolution. Lower molecular weight bands are presumed to be degradation products and/or polypeptides translated from alternative internal methionines. Immunoprecipitation. Immunoprecipitations were performed on in vitro translated proteins by mixing the translation reactions with 1 μg ofthe MLHl specific monoclonal antibody (mAB) MLHl 4 (Oncogene Science, Inc.), a polyclonal antibody generated to codons 2-20 of hPMS2 described above, or a polyclonal antibody generated to codons 843-862 of hPMS2 (Santa Cruz Biotechnology, Inc.) in 400 μl of EBC buffer (50 mM Tris, pH 7.5, 0.1 M NaCl, 0.5% NP40). After incubation for 1 hour at 4°C, protein A sepharose (Sigma) was added to a final concentration of 10% and reactions were incubated at 4°C for 1 hour. Proteins bound to protein A were washed five times in EBC and separated by electrophoresis on 4-20% Tris-glycine gels, which were then dried and autoradiographed. Example 5: Syrian hamster Tk-ts-13 Cells Produce a Novel Anti-Microbial Polypeptide Can Suppress the Growth of Bacillus subtilis The feasibility of creating microbial-resistant mammalian cells is demonstrated as follows. Syrian Hamster TK fibroblasts were transfected with a mammalian expression vector containing a novel anti-microbial polypeptide called mlgl or the empty expression vector called psg. When cells expressing the mlg polypeptide (referred to as TK-mlgl) were grown in the presence of Bacillus subtilis, these cells were able to suppress the growth ofthe microbes and allow the TK host to remain viable in contrast to TK cells transfected with the empty vector (TK=psg), which all died from the toxic effects that Bacillus subtilis has on mammalian cells. Figure 5 shows a photograph of TK-mlgl and TK=psg cultures grown in the presence of Bacillus for 4 days. Syrian hamster Tk-tsl3 cells were transfected with a eukaryotic expression vector that produces a novel antimicrobial polypeptide referred to as mlgl (Panel A) or the expression vector lacking an inserted cDNA for expression (TK=psg, Panel B). Cells were plated at a density of 5x10 5 cells/ml in a 10 cm falcon pyrogenic-free petri dish in growth medium for 24 hours and then inoculated with 10 μl of an exponentially growing culture of Bacillus subtilis. Cultures were then incubated for 4 days at which time Bacilli grow and begin to lyse the Tk-tsl3 parental culture as shown in panel B (indicated by arrows), while cells expressing the anti-microbial mlgl polypeptide (Panel A) remain viable in the presence of Bacillus (small granular structures present in panels A and B). These data demonstrate the feasibility of cells to survive in the presence of Bacillus contamination when they produce an anti-microbial agent. These data show that antimicrobial producing mammalian cells are capable of growing and surviving in the presence of toxic microbes. Cell lines and transfection. Syrian Hamster fibroblast Tk " tsl3 cells were obtained from ATCC and cultured as described. Modrich, Science, 1994, 266, 1959-1960. Stably transfected cell lines expressing hPMS2 were created by cotransfection ofthe PMS2 expression vectors and the pLHL4 plasmid encoding the hygromycin resistance gene at a ratio of 3:1 (pCAR:pLHL4) and selected with hygromycin. Stably transfected cell lines containing pCAR reporters were generated by co-transfection of pCAR vectors together with either pNTK plasmid encoding the neomycin resistance plasmid or with pLHL4. All transfections were performed using calcium phosphate as previously described in Modrich, Science, 1994, 266, 1959-1960, which is incorporated herein by reference in its entirety. Example 6: TK-hPMS2-134 Cells Can Suppress the Growth of Escherichia coli in vitro While TK-hPMS2-134 TK-tsl3 cells have been previously shown to be capable of altering genes in vivo (refer to Table 2 and Figure 1), the ability to generate "naturally microbial-resistant" clones has not been reported in the literature. To generate microbial- resistant TK cells, TK-tsl3 cells constitutively expressing the a dominant-negative mismatch repair gene, TK-hPMS2-134 or the empty vector (TKvect) that have been in culture for >3 months (~60 passages) were seeded at 5x10 5 cells/ml in Dulbelcco's Modified Eagles Medium (DMEM) plus 10% fetal bovine serum (FBS) and plated into 10 cm dishes (Falcon) in duplicate. These cells were grown overnight at 37°C in 5%CO 2 to allow cells to adhere to the plastic. The next day, TK cultures were inoculated with 10 μl of an exponentially growing culture of Escherichia coli. Cultures were then grown at 37°C in 5%CO 2 and observed on day 7 and 14 for microbial-resistant cell clones; these cells appear as clones of cells surrounded by "cleared" areas on the plate. At day 7, all cells in the control transfected TKvect culture were dead, while a subset of cells were viable in the TK-hPMS2-134 transfected cultures. At day 14, there were no clones in the control transfected TKvect cultures, while there were 34 and 40 Escherichia co/t-resistant colonies formed in the TK-hPMS2-134 transfected cultures. Growing clones from each dish were then pooled as individual cultures and grown to confluence. These cultures were named TK-hPMS2-134 (RI) and TK-hPMS2-134 (R2). Cultures were cured of Escherichia coli by the addition of 1 mg/ml G418, in which the TK-hPMS2-134 cells are resistant due to expression ofthe neomycin-resistance gene contained on the mammalian expression vector used to generate the cells. TKvect, TK-hPMS2-134 (RI) and TK-hPMS2-134 (R2) cells were plated at 5x10 5 cell/ml in 10 mis and plated into 10 cm dishes in duplicate. The next day, 10 μl of a logarithmic stage Escherichia coli culture was added to each TK culture and cultures were grown for 48 hours at 37°C in 5%CO 2 . An aliquot of supernatant from each culture was harvested immediately after inoculation to establish a baseline density of bacteria for each culture. After 48 hours, 2 ml of supernatant were harvested from each culture as well as from uninfected TK cultures. One ml of each supernatant was then analyzed by a spectrophotometer at an OD 600 to measure for bacterial density. Supernatants from uninfected cultures were used as a blank to correct for background. As shown in Figure 6, bacterial growth was significantly suppressed in TK-hPMS2-134 (RI) and TK-hPMS2- 134 (R2) cultures in contrast to TKvect control cells. These data demonstrate the feasibility of using a dominant-negative mismatch repair mutant hPMS2-134 on mammalian cells to produce genetically altered clones capable of producing a molecule(s) that can suppress microbial growth. As those skilled in the art will appreciate, numerous changes and modifications may be made to the preferred embodiments ofthe invention without departing from the spirit ofthe invention. It is intended that all such variations fall within the scope ofthe invention. In addition, the entire disclosure of each publication cited herein is hereby incorporated herein by reference.

Claims: What is claimed is: 1. A method for making a mammalian cell hypermutable, comprising: introducing into said mammalian cell a polynucleotide comprising a dominant-negative allele of a mismatch repair gene, whereby said cell becomes hypermutable. 2. The method of claim 1 wherein said polynucleotide is introduced into said cell by transfection in vitro. 3. The method of claim 1 , wherein said polynucleotide is introduced into said cell by transfection of an adherent cell in vitro. 4. The method of claim 1 wherein said mismatch repair gene is PMS2. 5. The method of claim 1 wherein said mismatch repair gene is human PMS2. 6. The method of claim 1 wherein said mismatch repair gene is human MLHl. I. The method of claim 1 wherein said mismatch repair gene is human PMS1. 8. The method of claim 1 wherein said mismatch repair gene is human MSH2. 9. The method of claim 4 wherein said allele comprises a truncation mutation. 10. The method of claim 4 wherein said allele comprises a truncation mutation at codon 134. I I . The method of claim 9 wherein said truncation mutation is a thymidine at nucleotide 424 of wild-type PMS2. 12. A homogeneous composition comprising a cultured, hypermutable, mammalian cell comprising a dominant negative allele of a mismatch repair gene. 13. The composition of claim 12 wherein said mismatch repair gene is PMS2. 14. The composition of claim 12 wherein said mismatch repair gene is human PMS2. 15. The composition of claim 12 wherein said mismatch repair gene is human MLHl . 16. The composition of claim 12 wherein said mismatch repair gene is human PMS1. 17. The composition of claim 12 wherein said mismatch repair gene is human MSH2. 18. The composition of claim 12 wherein said cell expresses a protein consisting of the first 133 amino acids of hPMS2. 19. A method for obtaining a mammalian cell that is resistant to a selected microbe comprising: growing a culture of mammalian cells wherein said cells have a dominant- negative allele of a mismatch repair gene; exposing said cells to said selected microbe; and selecting said mammalian cell that is resistant to said selected microbe. 20. The method of claim 19 wherein said hypermutable cell is selected for resistance to a gram-negative microbe. 21. The method of claim 19 wherein said hypermutable cell is selected for resistance to a gram-positive microbe. 22. The method of claim 19 wherein said hypermutable cell is selected for resistance to a protozoan. 23. The method of claim 19 wherein said hypermutable cell is selected for resistance to a bacteria. 24. The method of claim 19 wherein said hypermutable cell is selected for resistance to a fungi. 25. The method of claim 19 wherein said step of selecting for microbial resistance comprises isolating and testing conditioned medium from said hypermutable cell. 26. A method for obtaining a cell comprising a mutation in a gene encoding an antimicrobial activity comprising: growing a culture of mammalian cells having said gene encoding said antimicrobial activity, and a dominant negative allele of a mismatch repair gene; selecting a cell comprising said antimicrobial activity; and determining whether said gene comprises a mutation. 27. The method of claim 26 wherein said hypermutable cell is selected for resistance to a gram-negative microbe. 28. The method of claim 26 wherein said hypermutable cell is selected for resistance to a gram-positive microbe. 29. The method of claim 26 wherein said hypermutable cell is selected for resistance to a protozoan. 30. The method of claim 26 wherein said hypermutable cell is selected for resistance to a bacteria. 31. The method of claim 26 wherein said hypermutable cell is selected for resistance to a fungi. 32. The method of claim 26 wherein said step of selecting a cell for antimicrobial activity comprises isolating and testing conditioned medium from said hypermutable cell. 33. The method of claim 26 wherein said step of examining said cell to determine whether said gene comprises a mutation comprises analyzing a nucleotide sequence of said gene. 34. The method of claim 26 wherein said step of examining said cell to determine whether said gene comprises a mutation comprises analyzing mRNA transcribed from said gene. 35. The method of claim 26 wherein said step of examining said cell to determine whether said gene comprises a mutation comprises analyzing a protein encoded by said gene. 36. The method of claim 26 wherein said step of examining said cell to determine whether said gene comprises a mutation comprises analyzing the phenotype of said gene.

Inventors: GRASSO LUIGI, NICOLAIDES NICHOLAS C, SASS PHILIP M, GRASSO, LUIGI, NICOLAIDES, NICHOLAS, C., SASS, PHILIP, M.
Applicants: GRASSO LUIGI, MORPHOTEK INC, NICOLAIDES NICHOLAS C, SASS PHILIP M, GRASSO, LUIGI, MORPHOTEK INC., NICOLAIDES, NICHOLAS, C., SASS, PHILIP, M.
Application year: 2000
Main classification: C12N15
IPC codes: C07K14, C12N5, C12N9, C12N15