ESSENTIAL FUNGAL GENES AND THEIR USE

Abstract: Disclosed are essential Aspergillus polypeptides and genes (AN97, AN17, AN80, and AN85), as well as homologs thereof, which can be used to identify antifungal agents for treating fungal infections such as aspergillosis.

Description: ESSENTIAL FUNGAL GENES AND THEIR USE Background of the Invention The invention relates to essential fungal genes and their use in identifying antifungal agents. Fungal infections (mycoses) may be cutaneous, subcutaneous, or systemic. Superficial mycoses include tinea capitis, tinea corporis, tinea pedis, perionychomycosis, pityriasis versicolor, oral thrush, and other candidoses such as vaginal, respiratory tract, biliary, eosophageal , and urinary tract candidoses. Systemic mycoses include systemic and mucocutaneous candidosis, cryptococcosis, aspergillosis, mucormycosis (phycomycosis) , paracoccidioidomycosis, North American blastomycosis, histoplasmosis, coccidioidomycosis, and sporotrichosis . Fungal infections can also contribute to meningitis and pulmonary or respiratory tract diseases. Opportunistic fungal infections proliferate, especially in patients afflicted with AIDS or other diseases that compromise the immune system. Examples of pathogenic fungi include dermatophytes (e.g., Microsporum canis and other M. spp.; and Trichophyton spp . such as T. rubrum, and T. entagrophytes) , yeasts (e.g., Candida albicans, C. Tropicalis, or other Candida species) , Torulopsis glabrata, Epidermophyton floccosum, Malassezia furfur {Pi tyropsporon orbiculare, or P. ovale) , Cryptococcus neoformans, Aspergillus fumigatus, and other Aspergillus sp . , Zygomycetes (e.g., Rhizopus, Mucor) , Paracoccidioides brasiliensis, Blastomyces dermati tides, Histoplasma capsulatum, Coccidioides iπwni tis, and Sporothrix schenckii . Various strains of the fungus Aspergillus sp . cause aspergillosis, a potentially life-threatening disease in humans and other mammals. The clinical manifestations of aspergillosis in humans are very similar to those observed in rodents and cows. For example, necrosis, angioinvasion, and hematogenous dissemination are common features of aspergillosis in rodent and bovine model systems and in humans. In humans, aspergillosis typically is caused by inhalation of conidia (i.e., asexual spores produced by the fungus) . In cattle, pathogenic Aspergillus typically enter the animal through the forestomach and then disseminate through the blood of the animal. Putative virulence factors produced by pathogenic species of Aspergillus include hydroxymate siderophores (i.e., compounds that compete with human iron-binding proteins to acquire iron to support fungal growth) , lipids having the ability to inhibit complement and phagocytosis, and proteinases that can degrade elastin and other substrates. Summary of the Invention The invention is based on the discovery of four new genes in the fungus Aspergillus nidulans that are essential for survival. These genes are referred to herein as AN97, AN80, AN17, and AN85; for convenience, the polypeptides encoded by these genes are referred to herein as "AN polypeptides." The genes encoding the AN polypeptides are useful molecular tools for identifying similar genes in pathogenic microrganisms, such as pathogenic strains of Aspergillus (e.g. Aspergillus fumigatus and Aspergillus flavus) . In addition, the AN polypeptides and the essential genes encoding them are useful targets for identifying compounds that are inhibitors of the pathogens in which the AN polypeptides are expressed. Such inhibitors inhibit fungal growth by being fungistatic (e.g., inhibiting reproduction or cell division) or by being fungicidal (i.e., by causing cell death) . The invention, therefore, features an isolated AN97 polypeptide having the amino acid sequence set forth in SEQ ID NO:l, or conservative variations thereof. Nucleic acids encoding AN97 also are included within the invention. In particular, the invention includes an isolated nucleic acid of (a) SEQ ID NO:2, as depicted in Fig. 1, or degenerate variants thereof; (b) SEQ ID NO:2, or degenerate variants thereof, wherein T is replaced by U; (c) nucleic acids complementary to (a) and (b) ; and (d) fragments of (a) , (b) , and (c) that are at least 15 base pairs in length and that hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO : 1. The invention also features an isolated AN80 polypeptide having the amino acid sequence set forth in SEQ ID NO: 3, or conservative variations thereof. Nucleic acids encoding AN80 also are included. In particular, the invention includes an isolated nucleic acid of: (a) SEQ ID NO: , as depicted in Fig. 2, or degenerate variants thereof; (b) SEQ ID NO:4, or degenerate variants thereof, wherein T is replaced by U; (c) nucleic acids complementary to (a) and (b) ; and (d) fragments of (a) , (b) , and (c) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO : 3. The invention also includes an isolated AN85 polypeptide having the amino acid sequence set forth in SEQ ID NO: 5, or conservative variations thereof. Nucleic acids encoding AN85 also are included. In particular, the invention includes an isolated nucleic acid of: (a) SEQ ID NO: 6, as depicted in Fig. 3, or degenerate variants thereof; (b) SEQ ID NO: 6, or degenerate variants thereof, wherein T is replaced by U; (c) nucleic acids complementary to (a) and (b) ; and (d) fragments of (a) , (b) , and (c) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO: 5. The invention also features an isolated AN17 polypeptide having the amino acid sequence set forth in SEQ ID NO: 7, or conservative variations thereof. Nucleic acids encoding AN17 also are included. In particular, the invention includes an isolated nucleic acid of: (a) SEQ ID NO: 8, as depicted in Fig. 4, or degenerate variants thereof; (b) SEQ ID NO: 8, or degenerate variants thereof, wherein T is replaced by U; (c) nucleic acids complementary to (a) and (b) ; and (d) fragments of (a) , (b) , and (c) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO : 7. The invention also includes isolated nucleic acids that are at least 15 base pairs in length and which hybridize under stringent conditions to a nucleotide sequence selected from the group consisting of SEQ ID NO: 2, SEQ ID NO:4, SEQ ID NO: 6, and SEQ ID NO: 8. In addition, the invention includes allelic variants (i.e., genes encoding isozymes) of the genes encoding AN97, AN17, AN80, and AN85. For example, the invention includes genes that encode an AN polypeptide but which gene includes point mutation, deletion, promoter variant, or splice site variant, provided that the resulting AN polypeptide functions as an AN polypeptide (e.g., as determined in a complementation assay, as described herein and elsewhere) . Also included within the invention are isolated nucleic acid molecules containing the cDNA sequences contained with ATCC accession numbers 209471, 209472, 209473, and 209484 (deposited November 19, 1997), as well as polypeptides encoded by the cDNA sequences of these nucleic acid molecules. Identification of the AN97, AN17, AN80, and AN85 genes and the determination that they are essential allows homologs of these genes to be found in other organisms (e.g., fungi, such as yeast like S . cerevisiae; mammalian cells, such as human or murine cells; or plant cells) . Thus, the AN polypeptides used not only can be as a model for identifying similar essential genes in other Aspergillus strains, but also to identify homologous essential genes in other organisms, e.g., S. cerevisiae . Because such genes are homologs, they can be expected to be essential for survival without the need for extensive characterization of the homologous gene or polypeptide. Even though some such homologous genes may have previously been identified, the invention allows one to determine that such genes are essential for survival. Having identified such homologous genes as essential, these genes and the polypeptides encoded by these genes can be used to identify compounds that inhibit the growth of the host organism (e.g., compounds that are fungicidal or fungistatic against pathogenic strains of the organism) . As used herein, the term "yeast" refers to organisms of the order Saccharomycetales, which includes yeast such as Saccharomyces and Candida . As described below, several homologs of the AN polypeptides have been identified in the yeast S . cerevisiae and are essential for survival. Given the identification of such genes as essential in S. cerevisiae, homologs of these essential yeast genes can also be found in pathogenic yeast strains (e.g., Candida albicans) . The S . cerevisiae polypeptide and gene termed D9798.4 are homologs of the AN97 polypeptide and gene. The D9798.4 polypeptide and nucleic acid are depicted in Fig. 5, and are set forth in SEQ ID NOs : 9 and 10, respectively (GenBank Accession No. U32517) . As described herein, various methods of the invention can utilize the D9798.4 polypeptide or conservative variations thereof. Also useful are isolated nucleic acids of (a) SEQ ID NO: 10, as depicted in Fig. 5, or degenerate variants thereof; (b) SEQ ID NO: 10, or degenerate variants thereof, wherein T is replaced by U; (c) nucleic acids complementary to (a) and (b) ; and (d) fragments of (a) , (b) , and (c) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO: 9. Yeast homologs of the AN85 and AN80 polypeptides and genes also have been identified as being essential for survival, and these homologs can be used in the methods described herein. As described above for AN97, conservative variations, degenerate variants, complementary sequences, fragments, and nucleic acids in which T is replaced by U also can be used in various methods of the invention. Two homologs of AN85 have been identified. The amino acid and nucleic acid sequences of the AN85 homolog termed YGR010 are depicted in Fig. 6 (GenBank Accession No. Z72795) ; these sequences are set forth as SEQ ID NOs: 11 and 12, respectively. The amino acid and nucleic acid sequences of the AN85 homolog termed L8543.16 are depicted in Fig. 7 (GenBank Accession No. U20618) ; these sequences are set forth as SEQ ID NOs : 13 and 14, respectively. The AN80 polypeptide and gene have a homolog in yeast, termed L8004.2, the amino acid and nucleic acid sequences of which are depicted in Fig. 8 (GenBank Accession No. U53876) . These sequences are set forth as SEQ ID NOs: 15 and 16, respectively. The term AN97 polypeptide or gene as used herein is intended to include the polypeptide and gene set forth in Fig. 1 herein, as well as homologs of the sequences set forth in Fig. 1. For example, encompassed by the term AN97 gene are degenerate variants of the nucleic acid sequence set forth in Fig. 1. (SEQ ID NO:2) . Degenerate variants of a nucleic acid sequence exist because of the degeneracy of the amino acid code; thus, those sequences that vary from the sequence represented by SEQ ID N0:2, but which nonetheless encode an AN97 polypeptide are included within the invention. Likewise, because of the similarity in the structures of amino acids, conservative variations can be made in the amino acid sequence of the AN97 polypeptide while retaining the function of the polypeptide (e.g., as determined in a complementation assay, as described herein and elsewhere) . AN97 polypeptides and genes identified in additional Aspergillus strains may be such conservative variations or degenerate variants of the particular AN97 polypeptide and nucleic acid set forth in Fig. 1 (SEQ ID NOs : 1 and 2, respectively) . The AN97 polypeptide and gene share at least 80%, e.g., 90%, sequence identity with SEQ ID NOs : 1 and 2, respectively. Regardless of the percent sequence identity between the AN97 sequence and the sequence represented by SEQ ID NOs : 1 and 2, the AN97 genes and polypeptides encompassed by the invention are able to complement for the lack of AN97 function (e.g., in a temperature-sensitive mutant) in a standard complementation assay. AN97 genes that are identified and cloned from additional Aspergillus strains, and pathogenic strains in particular, can be used to produce AN97 polypeptides for use in the various methods described herein, e.g., for identifying antifungal agents. Likewise, the term AN80 encompasses homologues and conservative and degenerate variants of the sequences depicted in Fig. 2. Such homologues, conservative variations, and degenerate variants of AN17, AN85, and AN80 also are included within the invention. Excluded from the invention are the naturally-occurring homologs of AN polypeptides and nucleic acids found in S. cerevisiae (D9798.4, L8543.16, YGROIOW, and L8004.2), although methods employing such polypeptides and nucleic acids are encompassed by the invention. The AN97, AN17, AN80, and AN85 genes have been identified and shown to be essential for survival, these AN polypeptides and their yeast homologs (e.g., D9798.4, L8543.16, YGROIOW, and L8004.2) can be used to identify antifungal agents. More specifically, these AN polypeptides and their yeast homologs can be used, separately or together, in assays to identify test compounds which bind these polypeptides. Such test compounds are expected to be antifungal agents, in contrast to compounds that do not bind AN97, AN17, AN80, AN85, D9798.4, L8543.16, YGROIOW, and/or L8004.2. As described herein, any of a variety of art-known methods can be used to assay for binding of test compounds to the polypeptides. The invention includes, for example, a method for identifying an antifungal or anti-yeast agent where the method entails: (a) contacting an AN polypeptide, or homolog thereof, with a test compound; (b) detecting binding of the test compound to the AN polypeptide or homolog; and (c) determining whether a test compound that binds the AN polypeptide or homolog inhibits growth of fungi or yeast, relative to growth of fungi or yeast cultured in the absence of the test compound that binds the AN polypeptide or homolog, as an indication that the test compound is an antifungal or anti-yeast agent. In various embodiments, the AN polypeptide is derived from a non-pathogenic or pathogenic Aspergillus strain, such as Aspergillus nidulans, Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger. Preferably, homologs thereof are derived from the yeast Saccharomyces cerevisiae. The test compound can be immobilized on a substrate, and binding of the test compound to the AN polypeptide or homolog can be detected as immobilization of the AN polypeptide or homolog on the immobilized test compound, e.g., in an immunoassay with an antibody that specifically binds AN97. If desired, the test compound can be a test polypeptide (e.g., a polypeptide having a random or predetermined amino acid sequence; or a naturally-occurring or synthetic polypeptide) . Alternatively, the test compound can be a nucleic acid, such as a DNA or RNA molecule. In addition, small organic molecules can be tested. The test compound can be a naturally-occurring compound or it can be synthetically produced, if desired. Synthetic libraries, chemical libraries, and the like can be screened to identify compounds that bind the AN polypeptides. More generally, binding of test compound to the AN polypeptide or homolog can be detected either in vi tro or in vivo . Regardless of the source of the test compound, the AN polypeptides described herein can be used to identify compounds that are fungicidal or fungistatic to a variety of pathogenic or non-pathogenic strains. In an exemplary method, binding of a test compound to an AN polypeptide can be detected in a conventional two-hybrid system for detecting protein/protein interactions (e.g., in yeast or mammalian cells) . Generally, in such a method, (a) the AN polypeptide is provided as a fusion protein that includes the AN polypeptide fused to (i) a transcription activation domain of a transcription factor or (ii) a DNA-binding domain of a transcription factor; (b) the test polypeptide is provided as a fusion protein that includes the test polypeptide fused to (i) a transcription activation domain of a transcription factor or (ii) a DNA-binding domain of a transcription factor; and (c) binding of the test polypeptide to the AN polypeptide polypeptide is detected as reconstitution of a transcription factor. The yeast homologs can be used in similar methods. Reconstitution of the transcription factor can be detected, for example, by detecting transcription of a gene that is operably linked to a DNA sequence bound by the DNA-binding domain of the reconstituted transcription factor (See, for example, White, 1996, Proc. Natl. Acad. Sci. 93:10001-10003 and references cited therein and Vidal et al . , 1996, Proc. Natl. Acad. Sci. 93:10315- 10320) . In an alternative method, an isolated nucleic acid molecule encoding an AN polypeptides is used to identify a compound that decreases the expression of the AN polypeptide in vivo . Such compounds can be used as antifungal agents. To discover such compounds, cells that express an AN polypeptide are cultured, exposed to a test compound (or a mixture of test compounds) , and the level of expression or activity is compared with the level of AN polypeptide expression or activity in cells that are otherwise identical but that have not been exposed to the test compound (s) . Many standard quantitative assays of gene expression can be utilized in this aspect of the invention. In order to identify compounds that modulate expression of an AN polypeptide (or homologous sequence), the test compound (s) can be added at varying concentrations to the culture medium of cells that express an AN polypeptide (or homolog) , as described above. Such test compounds can include small molecules (typically, non-protein, non-polysaccharide chemical entities) , polypeptides, and nucleic acids. The expression of the AN polypeptide is then measured, for example, by Northern blot PCR analysis or RNAse protection analyses using a nucleic acid molecule of the invention as a probe. The level of expression in the presence of the test molecule, compared with the level of expression in its absence, will indicate whether or not the test molecule alters the expression of the AN polypeptide. Because the AN polypeptides are essential for survival, test compounds that inhibit the expression and/or function of the AN polypeptide will inhibit growth of the cells or kill the cells. Compounds that modulate the expression of the polypeptides of the invention can be identified by carrying out the assay described above and then measuring the levels of the AN polypeptides expressed in the cells, e.g., by performing a Western blot analysis using antibodies that bind an AN polypeptide . The invention further features methods of identifying from a large group of mutants those strains that have conditional lethal mutations. In general, the gene and corresponding gene product are subsequently identified, although the strains themselves can be used in screening or diagnostic assays. The mechanism (s) of action for the identified genes and gene products provide a rational basis for the design of anti-fungal therapeutic agents. These antifungal agents reduce the action of the gene product in a wild type strain, and therefore are useful in treating a subject with that type, or a similarly susceptible type of infection by administering the agent to the subject in a pharmaceutically effective amount. Reduction in the action of the gene product includes competitive inhibition of the gene product for the active site of an enzyme or receptor; non-competitive inhibition; disrupting an intracellular cascade path which requires the gene product; binding to the gene product itself, before or after post- translational processing; and acting as a gene product mimetic, thereby down-regulating the activity. Therapeutic agents include monoclonal antibodies raised against the gene product. Furthermore, the presence of the gene sequence in certain cells (e.g., a pathogenic fungus of the same genus or similar species) , and the absence or divergence of the sequence in host cells can be determined, if desired. Therapeutic agents directed toward genes or gene products that are not present in the host have several advantages, including fewer side effects, and lower overall dosage. The invention includes pharmaceutical formulations that include a pharmaceutically acceptable excipient and an antifungal agent identified using the methods described herein. In particular, the invention includes pharmaceutical formulations that contain antifungal agents that inhibit the growth of, or kill, pathogenic Aspergillus strains. Such pharmaceutical formulations can be used for treating an Aspergillus infection in an organism. Such a method entails administering to the organism a therapeutically effective amount of the pharmaceutical formulation. In particular, such pharmaceutical formulations can be used to treat aspergillosis in mammals such as humans and domesticated mammals (e.g., cows and pigs) . The efficacy of such antifungal agents in humans can be estimated in an animal model system well known to those of skill in the art (e.g., bovine and rodent (e.g., mouse) model systems) . These formulations also can be used to treat fungal infections in plants, e.g., by topically applying the antifungal agent to the plant. Alternatively, where the antifungal agent is a polypeptide or an antisense RNA, a gene encoding the polypeptide or expressing the antisense RNA can be transfected into the plant, using conventional techniques, and the polypeptide or antisense RNA can be expressed in the plant. Also included within the invention are polyclonal and monoclonal antibodies that specifically bind AN97, AN17, AN80, or AN85 polypeptide. Such antibodies can facilitate detection of AN polypeptides in various Aspergillus strains. These antibodies also are useful for detecting binding of a test compound to AN97, AN17, AN80, or AN85 polypeptides (e.g., using the assays described herein) . In addition, monoclonal antibodies that bind AN97, AN17, AN80, or AN85 polypeptide are themselves adequate antifungal agents when administered to a mammal, as such monoclonal antibodies are expected to impede one or more functions of AN97, AN17, AN80, or AN85 polypeptide. As used herein, "nucleic acids" encompass both RNA and DNA, including cDNA, genomic DNA, and synthetic (e.g., chemically synthesized) DNA. The nucleic acid may be double-stranded or single-stranded. Where single-stranded, the nucleic acid may be a sense strand or an antisense strand. The nucleic acid may be synthesized using oligonucleotide analogs or derivatives (e.g., inosine or phosphorothioate nucleotides) . Such oligonucleotides can be used, for example, to prepare nucleic acids that have altered base-pairing abilities or increased resistance to nucleases . An "isolated nucleic acid" is a DNA or RNA that is not immediately contiguous with both of the coding sequences with which it is immediately contiguous (one on the 5' end and one on the 3' end) in the naturally occurring genome of the organism from which it is derived. Thus, in one embodiment, an isolated nucleic acid includes some or all of the 5' non-coding (e.g., promoter) sequences that are immediately contiguous to the coding sequence. The term therefore includes, for example, a recombinant DNA that is incorporated into a vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule (e.g., a cDNA or a genomic DNA fragment produced by PCR or restriction endonuclease treatment) independent of other sequences. It also includes a recombinant DNA that is part of a hybrid gene encoding an additional polypeptide sequence. The term "isolated" can refer to a nucleic acid or polypeptide that is substantially free of cellular material, viral material, or culture medium (when produced by recombinant DNA techniques) , or chemical precursors or other chemicals (when chemically synthesized) . Moreover, an "isolated nucleic acid fragment" is a nucleic acid fragment that is not naturally occurring as a fragment and would not be found in the natural state . A nucleic acid sequence that is "substantially identical" to an AN97, AN17, AN80, or AN85 nucleotide sequence is at least 80% or 85% identical to the nucleotide sequence of the Aspergillus AN97, AN80, AN85, and AN17 nucleic acids of SEQ ID NO: 2, NO:4, NO : 6 , and NO : 8 , respectively, as depicted in Figs. 1, 2, 3, and 4, respectively. For purposes of comparison of nucleic acids, the length of the reference nucleic acid sequence will generally be at least 40 nucleotides, e.g., at least 60 nucleotides or more nucleotides. Sequence identity can be measured using sequence analysis software (e.g., Sequence Analysis Software Package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison, WI 53705) . The AN polypeptides of the invention include, but are not limited to, recombinant polypeptides and natural polypeptides. The invention also encompasses nucleic acid sequences that encode forms of AN97, AN17, AN80, or AN85 polypeptides in which naturally occurring amino acid sequences are altered or deleted. Preferred nucleic acids encode polypeptides that are soluble under normal physiological conditions. Also within the invention are nucleic acids encoding fusion proteins in which a portion of AN97, AN17, AN80, or AN85 is fused to an unrelated polypeptide (e.g., a marker polypeptide or a fusion partner) to create a fusion protein. For example, the polypeptide can be fused to a hexa-histidine tag to facilitate purification of bacterially expressed polypeptides, or to a hemagglutinin tag to facilitate purification of polypeptides expressed in eukaryotic cells. The invention also includes isolated, for example, polypeptides (and the nucleic acids that encode these polypeptides) that include a first portion and a second portion; the first portion includes, e.g., an AN polypeptide, and the second portion includes an immunoglobulin constant (Fc) region or a detectable marker. The fusion partner can be, for example, a polypeptide which facilitates secretion, e.g., a secretory sequence. Such a fused polypeptide is typically referred to as a preprotein. The secretory sequence can be cleaved by the host cell to form the mature protein. Also within the invention are nucleic acids that encode AN97, AN17, AN80, or AN85 fused to a polypeptide sequence to produce an inactive preprotein. Preproteins can be converted into the active form of the protein by removal of the inactivating sequence. The invention also includes nucleic acids that hybridize, e.g., under stringent hybridization conditions (as defined herein) to all or a portion of the nucleotide sequence of SEQ ID NOs: 2, 4, 6, or 8 , or their complements. The hybridizing portion of the hybridizing nucleic acids is typically at least 15 (e.g., 20, 30, or 50) nucleotides in length. The hybridizing portion of the hybridizing nucleic acid is at least 80%, e.g., at least 95%, or at least 98%, identical to the sequence of a portion or all of a nucleic acid encoding an AN97, AN17, AN80, or AN85 polypeptide. Hybridizing nucleic acids of the type described herein can be used as a cloning probe, a primer (e.g., a PCR primer), or a diagnostic probe. Nucleic acids that hybridize to the nucleotide sequences of SEQ ID NOs : 2 , 4, 6, or 8 are considered "antisense oligonucleotides." Also included within the invention are ribozymes that inhibit the function of AN97, AN17, AN80, or AN85, as determined, for example, in a complementation assay. In another embodiment, the invention features cells, e.g., transformed host cells, that contain a nucleic acid encompassed by the invention. A "transformed cell" is a cell into which (or into an ancestor of which) has been introduced, by means of recombinant DNA techniques, a nucleic acid encoding an AN polypeptide. Both prokaryotic and eukaryotic cells are included, e.g., bacteria, Aspergillus, yeast, and the like. The invention also features genetic constructs (e.g., vectors and plasmids) that include a nucleic acid of the invention which is operably linked to a transcription and/or translation sequence to enable expression, e.g., expression vectors. By "operably linked" is meant that a selected nucleic acid, e.g., a DNA molecule encoding an AN polypeptide, is positioned adjacent to one or more sequence elements, e.g., a promoter, which directs transcription and/or translation of the sequence such that the sequence elements can control transcription and/or translation of the selected nucleic acid. The invention also features purified or isolated AN97, AN17, AN80, and AN85 polypeptides. As used herein, both "protein" and "polypeptide" mean any chain of amino acids, regardless of length or post-translational modification (e.g., glycosylation or phosphorylation) . Thus, the terms "AN97 polypeptide" (or AN97) , "AN17 polypeptide" (or AN17) , "AN80 polypeptide" (or AN80) , or "AN85 polypeptide" (or AN85) include full-length, naturally occurring AN97, AN17, AN80, or AN85 proteins, respectively, as well as recombinantly or synthetically produced polypeptides that correspond to a full- length, naturally occurring AN97, AN17, AN80, or AN85 protein, or to a portion of a naturally occurring or synthetic AN97, AN17, AN80, or AN85 polypeptide. A "purified" or "isolated" compound is a composition that is at least 60% by weight the compound of interest, e.g., an AN97 polypeptide or antibody. Preferably the preparation is at least 75% (e.g., at least 90% or 99%) by weight the compound of interest . Purity can be measured by any appropriate standard method, e.g., column chromatography, polyacrylamide gel electrophoresis, or HPLC analysis. Preferred AN97, AN17, AN80, AN85 polypeptides include a sequence substantially identical to all or a portion of a naturally occurring AN97, AN17, AN80, or AN85 polypeptide, e.g., including all or a portion of the sequences shown in Figs. 1, 2, 3, and 4, respectively. Polypeptides "substantially identical" to the AN polypeptide sequences described herein have an amino acid sequence that is at least 80% or 85% (e.g., 90%, 95% or 99%) identical to the amino acid sequence of the AN97, AN80, AN85 or AN17 polypeptides of SEQ ID NOs:l, 3, 5, and 7, respectively. For purposes of comparison, the length of the reference AN polypeptide sequence will generally be at least 16 amino acids, e.g., at least 20 or 25 amino acids. In the case of polypeptide sequences that are less than 100% identical to a reference sequence, the non-identical positions are preferably, but not necessarily, conservative substitutions for the reference sequence. Conservative substitutions typically include substitutions within the following groups: glycine and alanine; valine, isoleucine, and leucine; aspartic acid and glutamic acid; asparagine and glutamine; serine and threonine; lysine and arginine; and phenylalanine and tyrosine. Where a particular polypeptide is said to have a specific percent identity to a reference polypeptide of a defined length, the percent identity is relative to the reference polypeptide. Thus, a polypeptide that is 50% identical to a reference polypeptide that is 100 amino acids long can be a 50 amino acid polypeptide that is completely identical to a 50 amino acid long portion of the reference polypeptide. It also might be a 100 amino acid long polypeptide which is 50% identical to the reference polypeptide over its entire length. Of course, other polypeptides also will meet the same criteria. The invention also features purified or isolated antibodies that specifically bind to an AN polypeptide. By "specifically binds" is meant that an antibody recognizes and binds a particular antigen, e.g., an AN97, AN17 polypeptide, but does not substantially recognize and bind other molecules in a sample, e.g., a biological sample that naturally includes AN97, AN17, AN80, or AN85. In one embodiment the antibody is a monoclonal antibody. In another aspect, the invention features a method for detecting an AN polypeptide in a sample. This method includes: obtaining a sample suspected of containing AN97, AN17, AN85, or AN80; contacting the sample with an antibody that specifically binds an AN97, AN17, AN85 or AN80 polypeptide under conditions that allow the formation of complexes of an antibody and AN97, AN17, AN85 or AN80; and detecting the complexes, if any, as an indication of the presence of AN97, AN17, AN85 or AN80 in the sample . Also encompassed by the invention is a method of obtaining a gene related to (i.e., a functional homologue of) the AN97, AN17, AN85, or AN80 gene. Such a method entails obtaining a labeled probe that includes an isolated nucleic acid which encodes all or a portion of AN97, AN17, AN85, or AN80, or a homolog thereof (e.g., D9798.4, L8543.16, YGROIOW, or L8004.2); screening a nucleic acid fragment library with the labeled probe under conditions that allow hybridization of the probe to nucleic acid fragments in the library, thereby forming nucleic acid duplexes; isolating labeled duplexes, if any; and preparing a full-length gene sequence from the nucleic acid fragments in any labeled duplex to obtain a gene related to the AN97, AN17, AN85, or AN80 gene. The invention offers several advantages. By combining gene knockout assays, as described herein, with assays of conditional sensitivity, we have identified genes that are truly essential, i.e., genes whose absence is fungicidal to Aspergillus . In addition, the methods for identifying antifungal agents can be configured for high throughput screening of numerous candidate antifungal agents. Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated herein by reference in their entirety. In the case of a conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative and are not intended to limit the scope of the invention, which is defined by the claims. Brief Description of the Drawings Fig. 1 is a representation of the amino acid and nucleic acid sequences of the AN97 polypeptide and gene from an Aspergillus nidulans strain (SEQ ID NOs : 1 and 2, respectively) . Fig. 2 is a representation of the amino acid and nucleic acid sequences of the AN80 polypeptide and gene from an Aspergillus nidulans strain (SEQ ID NOs : 3 and 4, respectively) . Fig. 3 is a representation of the amino acid and nucleic acid sequences of the AN85 polypeptide and gene from an Aspergillus nidulans strain (SEQ ID NOs : 5 and 6, respectively). Fig. 4 is a representation of the amino acid and nucleic acid sequences of the AN17 polypeptide and gene from an Aspergillus nidulans strain (SEQ ID NOs : 7 and 8, respectively) . Fig. 5 is a representation of the amino acid and nucleic acid sequences of the D9798.4 polypeptide and gene from S. cerevisiae (SEQ ID NOs : 9 and 10, respectively). Fig. 6 is a representation of the amino acid and nucleic acid sequences of the YGROIOW polypeptide and gene from S . cerevisiae (SEQ ID NOs: 11 and 12, respectively). Fig. 7 is a representation of the amino acid and nucleic acid sequences of the L8543.16 polypeptide and gene from S . cerevisiae (SEQ ID NOs: 13 and 14, respectively). Fig. 8 is a representation of the amino acid and nucleic acid sequences of the L8004.2 polypeptide and gene from S . cerevisiae (SEQ ID NOs:15 and 16, respectively). Detailed Description of the Invention Identifying Essential Aspercrillus Genes As shown by the experiments described below, expression of each of the AN97, AN17, AN80, and AN85 polypeptides is essential for survival of Aspergillus nidulans . Aspergillus nidulans is available from the ATCC (#FGSC4) . To identify genes for which inhibition of gene expression is fungicidal, various mutants of Aspergillus nidulans were assayed for conditional sensitivity. In general, mutagenesis of Aspergillus nidulans can be accomplished using any of various art-known methods. For example, exposure to ultraviolet light, x-rays, and/or chemical mutagens is acceptable. Examples of suitable chemical mutagens include ethylmethansulfonate (EMS) , metyhlmethanesulfonate (MMS) , methylnitrosoguanidine (NTG) , 4-nitroquinoline-l-oxide (NQO) , 2-aminopurine, 5-bromouracil , ICR 191 and other acridine derivatives, sodium bisulfite, ethidium bromide, nitrous acid, hydroxylamine, N-methyl-N' -nitroso-N-nitroguanidine, and alkylating agents (for further description of art-known mutagens and mutagenesis methods, see, e.g., Current Protocols in Molecular Biology, 1995 and Adelberg et al . , Biochem . Biophys . Res . Comm. 18:788, 1965). To identify conditional-sensitive mutants, mutagenized cells can be grown under (a) a first set of permissive conditions, then shifted to (b) restrictive conditions, and then to (c) a second set of permissive conditions. The cells of interest are those mutants that grow under the permissive conditions of (a) , but fail to grow under the restrictive conditions of (b) , and fail to recover under the permissive conditions of (c) . Ostensibly, any change in a growth parameter can serve as the "restrictive condition." For example, the restrictive conditions may be met by increasing or decreasing the temperature at which the cells are grown, thereby allowing the identification of temperature-sensitive mutants. For example, the optimal growth temperature for A . nidulans is 28°C, and a typical restrictive temperature is 42 °C. In alternative methods, the change to a restrictive condition may entail changing one or more of the following parameters of the growth conditions: pH, type and/or concentration of carbon and nitrogen sources, trace minerals, vitamins, salts, conidia- forming materials (e.g., DMSO, glycerol, and deuterated water), humidity, and the like. In general, permissive growth conditions allow the strains to grow at a rate that is at least 75% of that of the wild-type growth rate of Aspergillus . The second set of permissive conditions (in (c) ) can be the same as, or different from, the first permissive conditions. Typically, the cells are subjected to the second permissive conditions for at least 2 growth cycles (more typically, at least 5, 10, 15 or even 20 growth cycles) . Generally, the cells are subjected to the restrictive conditions for 2 to 20 growth cycles (typically 2-10 growth cycles) and for 24 hours or less. In practicing the invention, cell death (e.g., in (b) ) can be detected using any of a number of conventional criteria. For example, cell death can be detected macroscopically by observing that a colony of cells has approximately the same size, or a reduced size, after a length of time that is normally sufficient for several growth cycles under the second permissive conditions. Detection of cell death also can be facilitated by the use of light microscopy and cell staining to reveal cytological deformations and/or morphologies commonly known to be indicative of cell death. The absence of DNA, RNA, or protein synthesis also can signify cell death. Identification of Homologs of AN Polypeptides Having shown that the AN97, and AN80, and AN85 genes and polypeptides are essential for survival in Aspergillus, it can be expected that homologs of these polypeptides, when present in other organisms, for example pathogenic yeast, are essential for survival of those organisms as well. Using the sequences of the AN polypeptides identified in Aspergillus, homologs of these polypeptides were identified in the yeast S. cerevisiae . The coding sequences of AN97, AN80, and AN85 were used to search the GenBank database of nucleotide sequences to identify homologs of AN97, AN80, and AN85, respectively, which are essential genes in other organisms. Sequence comparisons were performed using the Basic Local Alignment Search Tool (BLAST) (Altschul et al . , J. Mol . Biol . , 215:403-410 1990). The percent sequence identity shared by the AN polypeptides and their homologs were determined using the GAP program from the Genetics Computer Group (GCG) Wisconsin Sequence Analysis Package (Wisconsin Package Version 9.0, GCG; Madison, WI) . The following parameters were used: gap creation penalty, 12 (protein) 50 (DNA) ; gap extension penalty, 4 (protein) 3 (DNA) . The percent sequence identity shared by the AN polypeptides and their homologs are summarized in Table 1. Typically, the AN polypeptides and their homologs share at least 25% (e.g., at least 40%) sequence identity. Typically, the DNA sequences encoding AN polypeptides and their homologs share at least 35% (e.g., at least 45%) sequence identity. Table 1: Sequence Identity Shared by AN Polypeptides and Their Homologues . To confirm that these yeast homologs of the 7ΛN polypeptides are essential for survival of yeast, the gene encoding each of the homologs was, separately, deleted from the S . cerevisiae genome. To this end, standard methods for making yeast "knock outs" were used, as described by Baudin et al . , Nucl . Acids . Res . 21:3329-3330, 1993. Briefly, a portion of the yeast genome was amplified in a polymerase chain reaction (PCR) that employed two primers. The primers for L8004.2 were 5 'AGGAAAGTAGCTATCGTAACGGGTACTAATAGTAATCTTGGTCTCTTGGCCTCCTCTAG3 ' (SEQ ID NO: 17) and 5 ' TACGCAGAGATATATTAAATGGGGGTTCTAGTTTCAACAATTTCGTTCAGAATGACACG3 ' (SEQ ID NO: 18) . The primers for D9798.4 were 5 ' TTAACAGCCGCGCCCATCATGCAAGATCCTGATGGTATTGACATTCTCTTGGCCTCCTCTAG3 ' (SEQ ID NO: 19) and 5 ' GCATATCAATTTTAACAGACCTCGCTGAAAGACTCTGAATCCTCGTTCAGAATGACACG3 ' (SEQ ID NO: 20) . These primers hybridized to a portion of the 5' and 3' sequences flanking the open reading frames of the yeast homologs and include nucleotides that are homologous to the HIS3 selectable marker. Following PCR amplification, the resulting crude mix was directly used to transform yeast, following a standard protocol . Identification of AN97, AN17, AN80, and AN85 Genes in Additional Aspercrillus Strains Now that the AN97, AN80, AN17, and AN85 genes and their yeast homologs, L8004.2, YGROIOW, L8543.16, and D9798.4, have been identified as essential for survival (as described below under "Examples"), these genes, or fragments thereof, can be used to detect homologous essential genes in other organisms. In particular, these genes can be used to analyze various pathogenic and non-pathogenic strains of Aspergillus (e.g., Aspergillus fumigatus , Aspergillus flavus and Aspergillus niger) and yeast (e.g., Candida albicans) . In particular, fragments of a nucleic acid (DNA or RNA) encoding an AN polypeptide or yeast homolog (or sequences complementary thereto) can be used as probes in conventional nucleic acid hybridization assays of pathogenic organisms (e.g., pathogenic Aspergillus strains). For example, nucleic acid probes (which typically are 8-30, or usually 15-20, nucleotides in length) can be used to detect the AN97, AN17, AN80, AN85 genes or homologs thereof in art-known molecular biology methods, such as Southern blotting, Northern blotting, dot or slot blotting, PCR amplification methods, colony hybridization methods, and the like. Typically, an oligonucleotide probe based on the nucleic acid sequences described herein, or fragments thereof, is labeled and used to screen a genomic library or a cDNA library constructed from mRNA obtained from an Aspergillus or yeast strain of interest. A suitable method of labeling involves using polynucleotide kinase to add 32 P-labeled ATP to the oligonucleotide used as the probe. This method is well known in the art, as are several other suitable methods (e.g., biotinylation and enzyme labeling). Hybridization of the oligonucleotide probe to the cDNA library, or other nucleic acid sample, typically is performed under moderate to high stringency conditions. Nucleic acid duplex or hybrid stability is expressed as the melting temperature or T m , which is the temperature at which a probe dissociates from a target DNA. This melting temperature is used to define the required stringency conditions. If sequences are to be identified that are related and substantially identical to the probe, rather than identical, then it is useful to first establish the lowest temperature at which only homologous hybridization occurs with a particular concentration of salt (e.g., SSC or SSPE) . Then, assuming that 1% mismatching results in a 1°C decrease in the T m , the temperature of the final wash in the hybridization reaction is reduced accordingly (for example, if sequences having > . 95% identity with the probe are sought, the final wash temperature is decreased by 5°C) . In practice, the change in T m can be between 0.5° and 1.5°C per 1% mismatch. As used herein, high stringency conditions include, for example, hybridizing at 68°C in 5x SSC/5x Denhardt's solution/1.0% SDS, or in 0.5 M NaHP0 4 (pH 7.2) /l mM EDTA/7% SDS, or in 50% formamide/0.25 M NaHP0 4 (pH 7.2) /0.25 M NaCl/1 mM EDTA/7% SDS; and washing in 0.2x SSC/O.1% SDS at room temperature or at 42°C, or in 0. lx SSC/0.1% SDS at 68°C, or in 40 mM NaHP0 4 (pH 7.2) /l mM EDTA/5% SDS at 50°C, or in 40 mM NaHP0 4 (pH 7.2) 1 mM EDTA/1% SDS at 50 °C. Moderately stringent conditions include washing in 3x SSC at 42 °C. The parameters of salt concentration and temperature can be varied to achieve the optimal level of identity between the probe and the target nucleic acid. Additional guidance regarding such conditions is readily available in the art, for example, by Sambrook et al . , 1989, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Press, N.Y.; and Ausubel et al . (eds.), 1995, Current Protocols in Molecular Biology, (John Wiley & Sons, N.Y.) at Unit 2.10. In one approach, cDNA libraries constructed from pathogenic or non-pathogenic Aspergillus or yeast strains can be screened. For example, such strains can be screened for AN97, AN17, AN85, or AN80 expression by Northern blot analysis. Upon detection of AN97, AN17, AN85, or AN80 transcripts or transcripts of homologs thereof, cDNA libraries can be constructed from RNA isolated from the appropriate strain, utilizing standard techniques well known to those of skill in the art. Alternatively, a total genomic DNA library can be screened using an AN97, AN17, AN85, or AN80 probe (or a probe directed to a homolog thereof) . New gene sequences can be isolated, for example, by performing PCR using two degenerate oligonucleotide primer pools designed on the basis of nucleotide sequences within the AN97, AN17, AN85 or AN80 genes, or their homologs, as depicted herein. The template for the reaction can be cDNA obtained by reverse transcription of mRNA prepared from strains known or suspected to express an AN97, AN17, AN85, or AN80 allele or an allele of a homolog thereof . The PCR product can be subcloned and sequenced to ensure that the amplified sequences represent the sequences of a new AN97, AN17, AN85, or AN80 nucleic acid sequence, or a sequence of a homolog thereof . The PCR fragment can then be used to isolate a full length cDNA clone by a variety of known methods. For example, the amplified fragment can be labeled and used to screen a bacteriophage cDNA library. Alternatively, the labeled fragment can be used to screen a genomic library. PCR technology also can be used to isolate full length cDNA sequences. For example, RNA can be isolated, following standard procedures, from an appropriate cellular or tissue source. A reverse transcription reaction can be performed on the RNA using an oligonucleotide primer specific for the most 5' end of the amplified fragment for the priming of first strand synthesis. The resulting RNA/DNA hybrid can then be "tailed" (e.g., with guanines) using a standard terminal transferase reaction, the hybrid can be digested with RNase H, and second strand synthesis can then be primed (e.g., with a poly-C primer) . Thus, cDNA sequences upstream of the amplified fragment can easily be isolated. For a review of useful cloning strategies, see e.g., Sambrook et al . , supra; and Ausubel et al . , supra . Now that the AN97, AN17, AN85, and AN80 genes and their homologs have been cloned, synthesis of the AN polypeptides or their homologs (or an antigenic fragment thereof) for use as antigens, or for other purposes, can readily be accomplished using any of the various art-known techniques. For example, an AN polypeptide or homolog, or an antigenic fragment (s) , can be synthesized chemically in vitro, or enzymatically (e.g., by in vi tro transcription and translation) . Alternatively, the gene can be expressed in, and the polypeptide purified from, a cell (e.g., a cultured cell) by using any of the numerous, available gene expression systems. For example, the polypeptide antigen can be produced in a prokaryotic host (e.g., E. coli or B . subtilis) or in eukaryotic cells, such as yeast cells or insect cells (e.g., by using a baculovirus-based expression vector) . Proteins and polypeptides can also be produced in plant cells, if desired. For plant cells viral expression vectors (e.g., cauliflower mosaic virus and tobacco mosaic virus) and plasmid expression vectors (e.g., Ti plasmid) are suitable. Such cells are available from a wide range of sources (e.g., the American Type Culture Collection, Rockland, MD; also, see, e.g., Ausubel et al . , Current Protocols in Molecular Biology, John Wiley & Sons, New York, 1994) . The optimal methods of transformation or transfection and the choice of expression vehicle will depend on the host system selected. Transformation and transfection methods are described, e.g., in Ausubel et al . , supra ; expression vehicles may be chosen from those provided, e.g., in Cloning Vectors : A Laboratory Manual (P.H. Pouwels et al . , 1985, Supp. 1987). The host cells harboring the expression vehicle can be cultured in conventional nutrient media, adapted as needed for activation of a chosen gene, repression of a chosen gene, selection of transformants, or amplification of a chosen gene . If desired, AN polypeptides or their homologs can be produced as fusion proteins. For example, the expression vector pUR278 (Ruther et al . , EMBO J. , 2:1791, 1983) can be used to create lacZ fusion proteins. The art-known pGEX vectors can be used to express foreign polypeptides as fusion proteins with glutathione S-transferase (GST) . In general, such fusion proteins are soluble and can be easily purified from lysed cells by adsorption to glutathione-agarose beads followed by elution in the presence of free glutathione. The pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned target gene product can be released from the GST moiety. In an exemplary insect cell expression system, a baculovirus such as Autographa californica nuclear polyhedrosis virus (AcNPV) , which grows in Spodoptera frugiperda cells, can be used as a vector to express foreign genes . A coding sequence encoding an AN polypeptide or homolog can be cloned into a non- essential region (for example the polyhedrin gene) of the viral genome and placed under control of a promoter, e.g., the polyhedrin promoter or an exogenous promoter. Successful insertion of a gene encoding an AN polypeptide or homolog can result in inactivation of the polyhedrin gene and production of non-occluded recombinant virus (i.e., virus lacking the proteinaceous coat encoded by the polyhedrin gene) . These recombinant viruses are then used to infect insect cells (e.g., Spodoptera frugiperda cells) in which the inserted gene is expressed (see, e.g., Smith et al . , J. Virol . , 46:584, 1983; Smith, U.S. Patent No. 4,215,051). In mammalian host cells, a number of viral-based expression systems can be utilized. When an adenovirus is used as an expression vector, the nucleic acid sequence encoding the AN polypeptide or homolog can be ligated to an adenovirus transcription/ translation control complex, e.g., the late promoter and tripartite leader sequence. This chimeric gene can then be inserted into the adenovirus genome by in vi tro or in vivo recombination. Insertion into a non-essential region of the viral genome (e.g., region El or E3) will result in a recombinant virus that is viable and capable of expressing an AN97, AN17, AN85, or AN80 gene product in infected hosts (see, e.g., Logan, Proc. Natl. Acad. Sci. USA, 81:3655, 1984). Specific initiation signals may be required for efficient translation of inserted nucleic acid sequences. These signals include the ATG initiation codon and adjacent sequences. In cases where an entire native gene (e.g., AN97) or cDNA, including its own initiation codon and adjacent sequences, is inserted into the appropriate expression vector, no additional translational control signals may be needed. In other cases, exogenous translational control signals, including, perhaps, the ATG initiation codon, should be provided. Furthermore, the initiation codon must be in phase with the reading frame of the desired coding sequence to ensure translation of the entire sequence. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic. The efficiency of expression may be enhanced by the inclusion of appropriate transcription enhancer elements, or transcription terminators (Bittner et al . , Methods in Enzymol . , 153:516, 1987) . The AN polypeptides and homologs can be expressed individually or as fusions with a heterologous polypeptide, such as a signal sequence or other polypeptide having a specific cleavage site at the N-and/or C-terminus of the protein or polypeptide. The heterologous signal sequence selected should be one that is recognized and processed, i.e., cleaved by a signal peptidase, by the host cell in which the fusion protein is expressed. A host cell can be chosen that modulates the expression of the inserted sequences, or modifies and processes the gene product in a specific, desired fashion. Such modifications (e.g., glycosylation) and processing (e.g., cleavage) of protein products may facilitate optimal functioning of the protein. Various host cells have characteristic and specific mechanisms for post-translational processing and modification of proteins and gene products. Appropriate cell lines or host systems familiar to those of skill in the art of molecular biology can be chosen to ensure the correct modification and processing of the foreign protein expressed. To this end, eukaryotic host cells that possess the cellular machinery for proper processing of the primary transcript, glycosylation, and phosphorylation of the gene product can be used. Such mammalian host cells include, but are not limited to, CHO, VERO, BHK, HeLa, COS, MDCK, 293, 3T3, WI38, and choroid plexus cell lines. If desired, the AN polypeptide or homolog thereof can be produced by a stably-transfected mammalian cell line. A number of vectors suitable for stable transection of mammalian cells are available to the public, see, e.g., Pouwels et al . (supra) ; methods for constructing such cell lines are also publicly known, e.g., in Ausubel et al . (supra) . In one example, cDNA encoding the protein is cloned into an expression vector that includes the dihydrofolate reductase (DHFR) gene. Integration of the plasmid and, therefore, the AN polypeptide-encoding gene into the host cell chromosome is selected for by including 0.01- 300 μM methotrexate in the cell culture medium (as described in Ausubel et al . , supra) . This dominant selection can be accomplished in most cell types. Recombinant protein expression can be increased by DHFR- mediated amplification of the transfected gene. Methods for selecting cell lines bearing gene amplifications are described in Ausubel et al . (supra) ; such methods generally involve extended culture in medium containing gradually increasing levels of methotrexate . DHFR-containing expression vectors commonly used for this purpose include pCVSEII-DHFR and pAdD26SV(A) (described in Ausubel et al . , supra) . A number of other selection systems can be used, including but not limited to the herpes simplex virus thymidine kinase, hypoxanthine-guanine phosphoribosyl-transferase, and adenine phosphoribosyltransferase genes can be employed in ti, hgprt , or aprt cells, respectively. In addition, gpt, which confers resistance to mycophenolic acid (Mulligan et al . , Proc. Natl . Acad. Sci . USA, 78:2072, 1981); neo, which confers resistance to the aminoglycoside G-418 (Colberre-Garapin et al . , J " . Mol . Biol . , 150:1, 1981); and hygro, which confers resistance to hygromycin (Santerre et al . , Gene, 30:147, 1981), can be used. Alternatively, any fusion protein can be readily purified by utilizing an antibody or other molecule that specifically binds the fusion protein being expressed. For example, a system described in Janknecht et al . , Proc. Natl . Acad . Sci . USA, 88:8972 (1981), allows for the ready purification of non- denatured fusion proteins expressed in human cell lines. In this system, the gene of interest is subcloned into a vaccinia recombination plasmid such that the gene's open reading frame is translationally fused to an amino-terminal tag consisting of six histidine residues. Extracts from cells infected with recombinant vaccinia virus are loaded onto Ni 2+ nitriloacetic acid-agarose columns, and histidine-tagged proteins are selectively eluted with imidazole-containing buffers. Alternatively, an AN polypeptide or homolog, or a portion thereof, can be fused to an immunoglobulin Fc domain. Such a fusion protein can be readily purified using a protein A column, for example. Moreover, such fusion proteins permit the production of a chimeric form of an AN polypeptide or homolog having increased stability in vivo . Once the recombinant AN polypeptide (or homolog) is expressed, it can be isolated (i.e., purified). Secreted forms of the polypeptides can be isolated from cell culture media, while non-secreted forms must be isolated from the host cells. Polypeptides can be isolated by affinity chromatography. For example, an anti-AN97 antibody (e.g., produced as described herein) can be attached to a column and used to isolate the protein. Lysis and fractionation of cells harboring the protein prior to affinity chromatography can be performed by standard methods (see, e.g., Ausubel et al . , supra) . Alternatively, a fusion protein can be constructed and used to isolate an AN polypeptide (e.g., an AN97-maltose binding fusion protein, an AN97-jS-galactosidase fusion protein, or an AN97-trpE fusion protein; see, e.g., Ausubel et al . , supra; New England Biolabs Catalog, Beverly, MA) . The recombinant protein can, if desired, be further purified, e.g., by high performance liquid chromatography using standard techniques (see, e.g., Fisher, Laboratory Techniques In Biochemistry And Molecular Biology, eds., Work and Burdon, Elsevier, 1980). Given the amino acid sequences described herein, polypeptides useful in practicing the invention, particularly fragments of AN97, AN17, AN85, AN80 from pathogenic Aspergillus strains, and fragments of D9798.4, L8004.2, L8543.16, and YGROIOW from yeast, can be produced by standard chemical synthesis (e.g., by the methods described in Solid Phase Peptide Synthesis, 2nd ed., The Pierce Chemical Co., Rockford, IL, 1984) and used as antigens, for example. Antibodies AN97, AN17, AN85, or AN80 polypeptides (or antigenic fragments or analogs of such polypeptide) can be used to raise antibodies useful in the invention, and such polypeptides can be produced by recombinant or peptide synthetic techniques (see, e.g., Solid Phase Peptide Synthesis, supra ; Ausubel et al . , supra) . Likewise, antibodies can be raised against the yeast homologs. In general, the polypeptides can be coupled to a carrier protein, such as KLH, as described in Ausubel et al . , supra, mixed with an adjuvant, and injected into a host mammal. Antibodies can be purified, for example, by affinity chromatography methods in which the polypeptide antigen is immobilized on a resin. In particular, various host animals can be immunized by injection of a polypeptide of interest. Examples of suitable host animals include rabbits, mice, guinea pigs, and rats. Various adjuvants can be used to increase the immunological response, depending on the host species, including but not limited to Freund's (complete and incomplete), adjuvant mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin, dinitrophenol , BCG (bacille Calmette-Guerin) and Corynebacterium parvum. Polyclonal antibodies are heterogeneous populations of antibody molecules derived from the sera of the immunized animals. Antibodies within the invention include monoclonal antibodies, polyclonal antibodies, humanized or chimeric antibodies, single chain antibodies, Fab fragments, F(ab') 2 fragments, and molecules produced using a Fab expression library. Monoclonal antibodies (mAbs) , which are homogeneous populations of antibodies to a particular antigen, can be prepared using the AN polypeptides or homologs thereof and standard hybridoma technology (see, e.g., Kohler et al . , Nature, 256:495, 1975; Kohler et al . , Eur. J. Immunol . , 6:511, 1976; Kohler et al., Eur. J. Immunol . , 6:292, 1976; Hammerling et al . , In Monoclonal Antibodies and T Cell Hybridomas, Elsevier, ΝY, 1981; Ausubel et al . , supra) . In particular, monoclonal antibodies can be obtained by any technique that provides for the production of antibody molecules by continuous cell lines in culture, such as those described in Kohler et al . , Nature, 256:495, 1975, and U.S. Patent No. 4,376,110; the human B-cell hybridoma technique (Kosbor et al . , Immunology Today, 4:72, 1983; Cole et al . , Proc . Natl . Acad . Sci . USA, 80:2026, 1983); and the EBV-hybridoma technique (Cole et al . , Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96, 1983). Such antibodies can be of any immunoglobulin class including IgG, IgM, IgE, IgA, IgD, and any subclass thereof. The hybridomas producing the mAbs of this invention can be cultivated in vi tro or in vivo . Once produced, polyclonal or monoclonal antibodies are tested for specific recognition of an AN polypeptide or homolog thereof in an immunoassay, such as a Western blot or immunoprecipitation analysis using standard techniques, e.g., as described in Ausubel et al . , supra . Antibodies that specifically bind to AN97, AN17, AN85, or AN80, or conservative variants and homologs thereof, are useful in the invention. For example, such antibodies can be used in an immunoassay to detect AN97 in pathogenic or non-pathogenic strains of Aspergillus (e.g., in Aspergillus extracts) . Preferably, antibodies of the invention are produced using fragments of the AN polypeptides that appear likely to be antigenic, by criteria such as high frequency of charged residues. In one specific example, such fragments are generated by standard techniques of PCR, and are then cloned into the pGEX expression vector (Ausubel et al . , supra) . Fusion proteins are expressed in E. coli and purified using a glutathione agarose affinity matrix as described in Ausubel, et al . , supra . If desired, several (e.g., two or three) fusions can be generated for each protein, and each fusion can be injected into at least two rabbits. Antisera can be raised by injections in a series, typically including at least three booster injections. Typically, the antisera is checked for its ability to immunoprecipitate a recombinant AN polypeptide or homolog, or unrelated control proteins, such as glucocorticoid receptor, chloramphenicol acetyltransferase, or luciferase. Techniques developed for the production of "chimeric antibodies" (Morrison et al . , Proc . Natl . Acad . Sci . , 81:6851, 1984; Neuberger et al . , Nature, 312:604, 1984; Takeda et al . , Nature, 314:452, 1984) can be used to splice the genes from a mouse antibody molecule of appropriate antigen specificity together with genes from a human antibody molecule of appropriate biological activity. A chimeric antibody is a molecule in which different portions are derived from different animal species, such as those having a variable region derived from a murine mAb and a human immunoglobulin constant region. Alternatively, techniques described for the production of single chain antibodies (U.S. Patent 4,946,778; and U.S. Patents 4,946,778 and 4,704,692) can be adapted to produce single chain antibodies against an AN polypeptide or homolog. Single chain antibodies are formed by linking the heavy and light chain fragments of the Fv region via an amino acid bridge, resulting in a single chain polypeptide. Antibody fragments that recognize and bind to specific epitopes can be generated by known techniques. For example, such fragments can include but are not limited to F(ab') 2 fragments, which can be produced by pepsin digestion of the antibody molecule, and Fab fragments, which can be generated by reducing the disulfide bridges of F(ab') 2 fragments. Alternatively, Fab expression libraries can be constructed (Huse et al., Science, 246:1275, 1989) to allow rapid and easy identification of monoclonal Fab fragments with the desired specificity. Polyclonal and monoclonal antibodies that specifically bind AN polypeptides or homologs can be used, for example, to detect expression of an AN97, AN17, AN85, AN80 gene or homolog in another strain of Aspergillus . For example, AN97 polypeptide can be readily detected in conventional immunoassays of Aspergillus cells or extracts. Examples of suitable assays include, without limitation, Western blotting, ELISAs, radioimmune assays, and the like. Assay for Antifungal Agents The invention provides a method for identifying an antifungal agent (s). Although the inventors are not bound by any particular theory as to the biological mechanism involved, the new antifungal agents are thought to inhibit specifically the function of the AN polypeptides or expression of the AN97, AN17, AN85, or AN80 genes, or homologs thereof. Screening for antifungal agents can be rapidly accomplished by identifying those compounds (e.g., polypeptides, ribonucleic acids (including ribozymes) , nucleic acids (including antisense nucleic acids) , or small molecules) that specifically bind to an AN polypeptide. A homolog of an AN polypeptide (e.g., D9798.4, L8004.2, L8543.16, or YGROIOW) can be substituted for the AN polypeptide in the methods summarized herein. Specific binding of a test compound to an AN polypeptide can be detected, for example, in vi tro by reversibly or irreversibly immobilizing the test compound(s) on a substrate, e.g., the surface of a well of a 96-well polystyrene microtitre plate. Methods for immobilizing polypeptides and other small molecules are well known in the art. For example, the microtitre plates can be coated with an AN polypeptide (or a combination of AN polypeptides and/or homologs) by adding the polypeptide (s) in a solution (typically, at a concentration of 0.05 to 1 mg/ml in a volume of 1-100 μl) to each well, and incubating the plates at room temperature to 37 °C for 0.1 to 36 hours. Polypeptides that are not bound to the plate can be removed by shaking the excess solution from the plate, and then washing the plate (once or repeatedly) with water or a buffer. Typically, the AN polypeptide or homolog is contained in water or a buffer. The plate is then washed with a buffer that lacks the bound polypeptide. To block the free protein-binding sites on the plates, the plates are blocked with a protein that is unrelated to the bound polypeptide. For example, 300 μl of bovine serum albumin (BSA) at a concentration of 2 mg/ml in Tris-HCl is suitable. Suitable substrates include those substrates that contain a defined cross-linking chemistry (e.g., plastic substrates, such as polystyrene, styrene, or polypropylene substrates from Corning Costar Corp. (Cambridge, MA), for example). If desired, a beaded particle, e.g., beaded agarose or beaded sepharose, can be used as the substrate. Binding of the test compound to the new AN polypeptides (or homologs thereof) can be detected by any of a variety of art- known methods. For example, an antibody that specifically binds an AN polypeptide can be used in an immunoassay. If desired, the antibody can be labeled (e.g., fluorescently or with a radioisotope) and detected directly (see, e.g., West and McMahon, J. Cell Biol . 74:264, 1977). Alternatively, a second antibody can be used for detection (e.g., a labeled antibody that binds the Fc portion of an anti-AN97 antibody) . In an alternative detection method, the AN polypeptide is labeled, and the label is detected (e.g., by labeling an AN polypeptide with a radioisotope, fluorophore, chromophore, or the like) . In still another method, the AN polypeptide is produced as a fusion protein with a protein that can be detected optically, e.g., green fluorescent protein (which can be detected under UV light) . In an alternative method, the AN polypeptide can be produced as a fusion protein with an enzyme having a detectable enzymatic activity, such as horse radish peroxidase, alkaline phosphatase, ce-galactosidase, or glucose oxidase. Genes encoding all of these enzymes have been cloned and are readily available for use by those of skill in the art. If desired, the fusion protein can include an antigen, and such an antigen can be detected and measured with a polyclonal or monoclonal antibody using conventional methods. Suitable antigens include enzymes (e.g., horse radish peroxidase, alkaline phosphatase, and cϋ-galactosidase) and non-enzymatic polypeptides (e.g., serum proteins, such as BSA and globulins, and milk proteins, such as caseins) . In various in vivo methods for identifying polypeptides that bind AN polypeptides, the conventional two-hybrid assays of protein/protein interactions can be used (see e.g., Chien et al., Proc . Natl . Acad . Sci . USA, 88:9578, 1991; Fields et al . , U.S. Pat. No. 5,283,173; Fields and Song, Nature, 340:245, 1989; Le Douarin et al . , Nucleic Acids Research, 23:876, 1995; Vidal et al., Proc . Natl . Acad . Sci . USA, 93:10315-10320, 1996; and White, Proc . Natl . Acad. Sci . USA, 93:10001-10003, 1996). Kits for practicing various two-hybrid methods are commercially available (e.g., from Clontech; Palo Alto, CA) . Generally, the two-hybrid methods involve in vivo reconstitution of two separable domains of a transcription factor. The DNA binding domain (DB) of the transcription factor is required for recognition of a chosen promoter. The activation domain (AD) is required for contacting other components of the host cell's transcriptional machinery. The transcription factor is reconstituted through the use of hybrid proteins. One hybrid is composed of the AD and a first protein of interest . The second hybrid is composed of the DB and a second protein of interest. In cases where the first and second proteins of interest interact with each other, the AD and DB are brought into close physical proximity, thereby reconstituting the transcription factor. Association of the proteins can be measured by assaying the ability of the reconstituted transcription factor to activate transcription of a reporter gene . Useful reporter genes are those that are operably linked to a promoter which is specifically recognized by the DB. Typically, the two-hybrid system employs the yeast Saccharomyces cerevisiae and reporter genes, the expression of which can be selected under appropriate conditions. Other eukaryotic cells, including mammalian and insect cells, can be used, if desired. The two-hybrid system provides a convenient method for cloning a gene encoding a polypeptide (i.e., a candidate antifungal agent) that binds a second, preselected polypeptide (e.g., AN97) . Typically, though not necessarily, a cDNA library is constructed such that randomly generated sequences are fused to the AD, and the protein of interest (e.g., AN97 or AN80) is fused to the DB . In such two-hybrid methods, two fusion proteins are produced. One fusion protein contains the AN polypeptide (or homolog thereof) fused to either a transactivator domain or DNA binding domain of a transcription factor (e.g., of Gal4) . The other fusion protein contains a test polypeptide fused to either the DNA binding domain or a transactivator domain of a transcription factor. Once brought together in a single cell (e.g., a yeast cell or mammalian cell), one of the fusion proteins contains the transactivator domain and the other fusion protein contains the DNA binding domain. Therefore, binding of the AN polypeptide to the test polypeptide (i.e., candidate antifungal agent) reconstitutes the transcription factor. Reconstitution of the transcription factor can be detected by detecting expression of a gene (i.e., a reporter gene) that is operably linked to a DNA sequence that is bound by the DNA binding domain of the transcription factor. The methods described above can be used for high throughput screening of numerous test compounds to identify candidate antifungal (or anti-yeast) agents. Having identified a test compound as a candidate antifungal agent, the candidate antifungal agent can be further tested for inhibition of fungal growth in vi tro or in vivo (e.g., using an animal, e.g., rodent, model system) if desired. Using other, art-known variations of such methods, one can test the ability of a nucleic acid (e.g., DNA or RNA) used as the test compound to bind an AN polypeptide or homolog thereof. In vi tro, further testing can be accomplished by means known to those in the art such as an enzyme inhibition assay or a whole-cell fungal growth inhibition assay. For example, an agar dilution assay identifies a substance that inhibits fungal growth. Microtiter plates are prepared with serial dilutions of the test compound; adding to the preparation a given amount of growth substrate; and providing a preparation of Aspergillus spores. Inhibition of growth is determined, for example, by observing changes in optical densities of the fungal cultures. Inhibition of fungal growth is demonstrated, for example, by comparing (in the presence and absence of a test compound) the rate of growth or the absolute growth of fungal sporulation or nuclei. Inhibition includes a reduction of one of the above measurements by at least 20% (e.g., at least 25%, 30%, 40%, 50%, 75%, 80%, or 90%) . Rodent (e.g., murine) and bovine animal models of aspergillosis are known to those of skill in the art, and such animal model systems are accepted for screening antifungal agents as an indication of their therapeutic efficacy in human patients (Rhodes et al . , J. Med. and Vet . Myco . , 30:51-57, 1992) . Indeed, the clinical manifestations of bovine aspergillosis show many pathological similarities to aspergillosis in humans and rodents. In a typical in vivo assay, an animal is infected with a pathogenic Aspergillus strain, e.g., by inhalation of Aspergillus spores (i.e., conidia) , and conventional methods and criteria are used to diagnose the mammal as being afflicted with aspergillosis. The candidate antifungal agent then is administered to the mammal at a dosage of 1-100 mg/kg of body weight, and the mammal is monitored for signs of amelioration of disease. Alternatively, the test compound can be administered to the mammal prior to infecting the mammal with Aspergillus, and the ability of the treated mammal to resist infection is measured. Of course, the results obtained in the presence of the test compound are compared with results in control animals, which are not treated with the test compound. Administration of candidate antifungal agent to the mammal can be carried out as described below, for example . Antisense Methods Antisense approaches involve the design of oligonucleotides (either DNA or RNA) that are complementary to AN97, AN17, AN80, or AN85 mRNA. The antisense oligonucleotides bind to the AN97, AN17, AN80, or AN85 coding sequences and/or mRNA transcripts and inhibit transcription and/or translation. Absolute ■ complementarity is not required. A sequence "complementary" to a portion of an RNA, as referred to herein, means a sequence having sufficient complementarity to be able to hybridize with the RNA and form a stable duplex; in the case of double-stranded antisense nucleic acids, a single strand of the duplex DNA can be tested, or triplex formation can be assayed. The ability to hybridize will depend on both the degree of complementarity and the length of the antisense nucleic acid. Generally, the longer the hybridizing nucleic acid, the more base mismatches with an RNA it may contain and still form a stable duplex (or triplex, as the case may be) . One skilled in the art can ascertain a tolerable degree of mismatch by use of standard procedures to determine the melting point of the hybridized complex. Oligonucleotides that are complementary to the 5' end of the message, e.g., the 5' untranslated sequence up to and including the AUG initiation codon, should work most efficiently at inhibiting translation. However, sequences complementary to the 3' untranslated sequences of mRNAs have been shown to be effective at inhibiting translation of mRNAs as well (Wagner, Nature, 372:333, 1984). Thus, oligonucleotides complementary to either the 5'- or 3'- non-translated, non-coding regions of the AN97, AN17, AN80, or AN85 genes, or their yeast homologs D9798.4, L8543.16, YGROIOW, of L8004.2, as represented by SEQ ID NOs:2, 4, 6, 8, 10, 12, 14, and 16 can be used in an antisense approach to inhibit translation of the endogenous sequences. Oligonucleotides complementary to the 5' untranslated region of the mRNA typically also include the complement of the AUG start codon. Antisense oligonucleotides complementary to mRNA coding regions are less preferred inhibitors of translation, but can be used in accordance with the invention. Whether designed to hybridize to the 5'-, 3'-, or coding region of the mRNA, antisense nucleic acids should be at least six nucleotides in length (e.g., oligonucleotides ranging from 6 to about 50 nucleotides in length) . In specific aspects, the oligonucleotide is at least 10 nucleotides, at least 15 nucleotides, or at least 25 nucleotides. Regardless of the choice of target sequence, in vi tro studies typically are first performed to quantitate the ability of the antisense oligonucleotide to inhibit gene expression. Typically, these studies utilize controls that distinguish between antisense gene inhibition and nonspecific biological effects of oligonucleotides. Generally, these studies compare levels of the target RNA or protein with that of an internal control RNA or protein. Additionally, it is envisioned that results obtained using the antisense oligonucleotide are compared with those obtained using a control oligonucleotide. Typically, the control oligonucleotide is of approximately the same length as the test oligonucleotide and that the nucleotide sequence of the oligonucleotide differs from the antisense sequence no more than is necessary to prevent specific hybridization to the target sequence. The antisense oligonucleotides can be DNA or RNA, or chimeric mixtures, or derivatives or modified versions thereof, and can be single-stranded or double-stranded. The oligonucleotides can be modified at the base moiety, sugar moiety, or phosphate backbone, for example, to improve stability of the molecule, hybridization, etc. The oligonucleotide may include other appended groups such as peptides (e.g., for targeting host cell receptors in vivo) , or agents facilitating transport across the cell membrane (as described, e.g., in Letsinger et al . , Proc . Natl . Acad . Sci . USA, 86:6553, 1989; Lemaitre et al . , Proc. Natl . Acad. Sci . USA, 84:648, 1987; PCT Publication No. WO 88/09810) or the blood-brain barrier (see, e.g., PCT Publication No. WO 89/10134), or hybridization- triggered cleavage agents (see, e.g., Krol et al . , BioTechniques , 6:958, 1988), or intercalating agents (see, e.g., Zon, Pharm . Res . , 5:539, 1988). To this end, the oligonucleotide can be conjugated to another molecule, e.g., a peptide, hybridization triggered cross-linking agent, transport agent, or hybridization-triggered cleavage agent. The antisense oligonucleotide can include at least one modified base moiety selected from the group including, but not limited to, 5-fluorouracil , 5-bromouracil , 5-chlorouracil , 5- iodouracil, hypoxanthine , xantine, 4 -acetylcytosine, 5- (carboxyhydroxylmethyl) uracil, 5-carboxymethylaminomethyl-2- thiouridine, 5-carboxymethyl-aminomethyluracil , dihydrouracil , beta-D-galactosylqueosine, inosine, N6-isopentenyladenine, 1- methylguanine, 1-methylinosine, 2 , 2-dimethylguanine, 2- methyladenine, 2 -methylguanine, 3-methylcytosine, 5- methylcytosine, N6-adenine, 7-methylguanine, 5- methylaminomethyluracil, 5-methoxyaminomethyl-2-thiouracil, beta-D-mannosylqueosine, 5' -methoxycarboxymethyluracil , 5- methoxyuracil, 2-methylthio-N6-isopentenyladenine, uracil-5- oxyacetic acid (v) , wybutoxosine, pseudouracil , queosine, 2- thiocytosine, 5-methyl-2-theouracil, 2-thiouracil, 4-thiouracil , 5-methyluracil, uracil-5-oxyacetic acid methylester, uracil-5- oxyacetic acid (v) , 5-methyl-2-thiouracil, 2- (3-amino-3-N-2 - carboxypropyl) uracil, (acp3)w, and 2 , 6-diaminopurine. The antisense oligonucleotide can also include at least one modified sugar moiety selected from the group including, but not limited to, arabinose, 2-fluoroarabinose, xylulose, and hexose . In yet another embodiment, the antisense oligonucleotide includes at least one modified phosphate backbone, e.g., a phosphorothioate, a phosphorodithioate, a phosphoramidothioate, a phosphoramidate, a phosphorodiamidate, a methylphosphonate, an alkyl phosphotriester, and a formacetal, or an analog of any of these backbones . In addition, the antisense oligonucleotide can be an a- anomeric oligonucleotide that forms specific double-stranded hybrids with complementary RNA in which, contrary to the usual jS-units, the strands run parallel to each other (Gautier et al . , Nucl . Acids . Res . , 15:6625, 1987). The oligonucleotide can be a 2' -O-methylribonucleotide (Inoue et al . , Nucl . Acids Res . , 15:6131, 1987), or a chimeric RNA-DNA analog (Inoue et al . , FEBS Lett . , 215:327, 1987) . Antisense oligonucleotides of the invention can be synthesized by standard methods known in the art, e.g., by use of an automated DNA synthesizer (such as are commercially available from Biosearch, Applied Biosystems, etc.). As examples, phosphorothioate oligonucleotides can be synthesized by the method of Stein et al . , Nucl . Acids Res . , 16:3209, 1988, and methylphosphonate oligonucleotides can be prepared by use of controlled pore glass polymer supports (Sarin et al . , Proc . Natl . Acad . Sci . USA, 85:7448, 1988) . While antisense nucleotides complementary to the AN97, AN17, AN80, AN85, D9798.4, L8543.16, YGROIOW, or L8004.2 coding region sequence could be used, those complementary to the transcribed untranslated region are preferred. Generally, such antisense oligonucleotides are 10-100 nucleotides in length (e.g., 15-50 nucleotides). Pathogenic microorganisms, such as Aspergillus, can spontaneously phagocytose oligonucleotides. Accordingly, these antisense oligonucleotides can be administered systemically or locally to a patient suffering from a pathogen infection in order to deliver the antisense oligonucleotides to the infectious organism in a method of treatment. For example, such antisense oligonucleotides can be used to inhibit expression of an AN polypeptide and thereby treat or inhibit fungal infections. A suitable approach uses a recombinant DNA construct in which the antisense oligonucleotide is placed under the control of a strong pol III or pol II promoter. The use of such a construct to transfect fungal cells in the patient will result in the transcription of sufficient amounts of single stranded nucleic acids that form complementary base pairs with the endogenous transcripts encoding AN polypeptides and thereby prevent translation of the mRNA. For example, a vector can be introduced in vivo such that it is taken up by a cell and directs the transcription of an antisense RNA. Such a vector can remain episomal or become chromosomally integrated, as long as it can be transcribed to produce the desired antisense RNA. Appropriate vectors can be constructed by recombinant DNA technology methods standard in the art. Vectors can be plasmid, viral, or others known in the art, used for replication and expression in fungal cells. Expression of the sequence encoding the antisense RNA can be by any promoter known in the art to act in fungi, e.g. Aspergillus, cells. Such promoters can be inducible or constitutive, such as an alcohol dehydrogenase promoter (e.g., alcA) and a nitrate reductase promoter (e.g., niiA) . Any type of plasmid, cosmid, or viral vector can be used to prepare the recombinant DNA construct which can be administered systemically or directly to the infected tissue. Ribozymes Ribozyme molecules designed to catalytically cleave mRNA transcripts encoding AN polypeptides also can be used to prevent translation of mRNA and expression of the AN polypeptides (see, e.g., PCT Publication WO 90/11364; Saraver et al . , Science, 247:1222, 1990). Various ribozymes that cleave mRNA at site- specific recognition sequences can be used to destroy mRNAs encoding the AN polypeptides (e.g., the use of hammerhead ribozymes) . Hammerhead ribozymes cleave mRNAs at locations dictated by flanking regions that form complementary base pairs with the target mRNA. It is recommended that the target mRNA have the following sequence of two bases: 5'-UG-3'. The construction and production of hammerhead ribozymes is known in the art (Haseloff et al . , Nature, 334:585, 1988). There are numerous examples of potential hammerhead ribozyme cleavage sites within the nucleotide sequence of cDΝAs encoding AN polypeptides (Figs. 1 to 3). Typically, the ribozyme is engineered so that the cleavage recognition site is located near the 5' end of the mRNA encoding the AN polypeptide in order to increase efficiency and minimize the intracellular accumulation of non-functional mRNA transcripts. The ribozymes of the present invention also include RNA endoribonucleases (hereinafter "Cech-type ribozymes"), such as the one that occurs naturally in Tetrahymena Thermophila (known as the IVS or L-19 IVS RNA) , and which has been extensively described by Cech and his collaborators (Zaug et al . , Science, 224:574, 1984; Zaug et al . , Science, 231:470, 1986; Zug et al . , Nature, 324:429, 1986; PCT Application No. WO 88/04300; and Been et al., Cell , 47:207, 1986). The Cech-type ribozymes have an eight base-pair sequence that hybridizes to a target RNA sequence, whereafter cleavage of the target RNA takes place. The invention encompasses those Cech-type ribozymes that target eight base-pair active site sequences present in AN polypeptides . As in the antisense approach, the ribozymes can be composed of modified oligonucleotides (e.g., for improved stability, targeting, etc.), and should be delivered to cells that express the AN polypeptide. A typical method of delivery involves using a DNA construct "encoding" the ribozyme under the control of a strong constitutive promoter, e.g., a pol III or pol II promoter, so that transfected cells will produce sufficient quantities of the ribozyme to destroy endogenous mRNAs encoding AN polypeptides and inhibit translation thereof. Because ribozymes, unlike typical antisense molecules, are catalytic, a lower intracellular concentration is required for efficiency. Pharmaceutical Formulations Treatment includes administering a pharmaceutically effective amount of a composition containing an antifungal agent to a subject in need of such treatment, thereby inhibiting fungal growth in the subject. Such a composition typically contains from about 0.1 to 90% by weight (such as 1 to 20% or 1 to 10%) of an antifungal agent of the invention in a pharmaceutically acceptable carrier. Solid formulations of the compositions for oral administration may contain suitable carriers or excipients, such as corn starch, gelatin, lactose, acacia, sucrose, microcrystalline cellulose, kaolin, mannitol, dicalcium phosphate, calcium carbonate, sodium chloride, or alginic acid. Disintegrators that can be used include, without limitation, micro-crystalline cellulose, corn starch, sodium starch glycolate and alginic acid. Tablet binders that may be used include acacia, methylcellulose, sodium carboxymethylcellulose, polyvinylpyrrolidone (Povidone) , hydroxypropyl methylcellulose, sucrose, starch, and ethylcellulose . Lubricants that may be used include magnesium stearates, stearic acid, silicone fluid, talc, waxes, oils, and colloidal silica. Liquid formulations of the compositions for oral administration prepared in water or other aqueous vehicles may contain various suspending agents such as methylcellulose, alginates, tragacanth, pectin, kelgin, carrageenan, acacia, polyvinylpyrrolidone, and polyvinyl alcohol. The liquid formulations may also include solutions, emulsions, syrups and elixirs containing, together with the active compound (s), wetting agents, sweeteners, and coloring and flavoring agents. Various liquid and powder formulations can be prepared by conventional methods for inhalation into the lungs of the mammal to be treated. Injectable formulations of the compositions may contain various carriers such as vegetable oils, dimethylacetamide, dimethylformamide, ethyl lactate, ethyl carbonate, isopropyl myristate, ethanol, polyols (glycerol, propylene glycol, liquid polyethylene glycol, and the like). For intravenous injections, water soluble versions of the compounds may be administered by the drip method, whereby a pharmaceutical formulation containing the antifungal agent and a physiologically acceptable excipient is infused. Physiologically acceptable excipients may include, for example, 5% dextrose, 0.9% saline, Ringer's solution or other suitable excipients. Intramuscular preparations, a sterile formulation of a suitable soluble salt form of the compounds can be dissolved and administered in a pharmaceutical excipient such as Water-for-Injection, 0.9% saline, or 5% glucose solution. A suitable insoluble form of the compound may be prepared and administered as a suspension in an aqueous base or a pharmaceutically acceptable oil base, such as an ester of a long chain fatty acid, (e.g., ethyl oleate) . A topical semi-solid ointment formulation typically contains a concentration of the active ingredient from about 1 to 20%, e.g., 5 to 10% in a carrier such as a pharmaceutical cream base. Various formulations for topical use include drops, tinctures, lotions, creams, solutions, and ointments containing the active ingredient and various supports and vehicles. The optimal percentage of the antifungal agent in each pharmaceutical formulation varies according to the formulation itself and the therapeutic effect desired in the specific pathologies and correlated therapeutic regimens. Appropriate dosages of the antifungal agents can readily be determined by those of ordinary skill in the art of medicine by monitoring the mammal for signs of disease amelioration or inhibition, and increasing or decreasing the dosage and/or frequency of treatment as desired. The optimal amount of the antifungal compound used for treatment of conditions caused by or contributed to by fungal infection may depend upon the manner of administration, the age and the body weight of the subject and the condition of the subject to be treated. Generally, the antifungal compound is administered at a dosage of 1 to 100 mg/kg of body weight, and typically at a dosage of 1 to 10 mg/kg of body weight. Example In this example, the identification and cloning of AN97, AN17, AN85, and AN80 are described. A library of approximately 1,000 A . nidulans mutants was obtained, which was prepared using 4-nitroquinoline as a mutagen, as described previously (Harris et al . , Genetics 136:517-532 1994). To identify strains having a temperature- sensitive mutation in an essential gene, the collection of 1,000 strains was grown at the permissive temperature of 28 °C for 16 hours in minimal medium (MN; pH 6.5, 1% glucose, nitrate salts and trace elements as described in Kafer, Adv. Genet . 19:33-131, 1977) . The trace element solution was stored at 4° in the dark; each liter contained 40 mg Na 2 B 4 0 7 (10 H 2 0) , 400 mg cupric sulfate (5 H 2 0) , 1 g ferric phosphate (4 H 2 0) , 600 mg manganese sulfate (4 H 2 0) , 800 mg disodium molybdate (2 H 2 0) , and 8 g zinc sulfate (7 H 2 0) . Slat solution was stored at 4° C after adding 2 ml chloroform as a preservative; each liter contained 26 g potassium chloride, 26 g magnesium sulfate (7 H 2 0) 76 g monobasic potassium phosphate and 50 mL trace element solution. Supplement solution was sterilized by autoclaving for 15 minutes and stored in a light-proof container due to the reactivity of riboflavin. Each liter contains 100 mg nicotinic acid, 250 mg riboflavin, 200 mg pantothenic acid, 50 mg pyridoxin, 1 mg biotin, and 20 mg p-aminobenzoic acid. Condidia (2 x 10 6 /ml in sterile, distilled water) were mutagenized with NQO (4 μg/ml) for 30 minutes at 37° C with constant shaking. Diluting the conidia with an equal volume of 5% sodium thiosulfate inactivated the NQO. Mutagenized conidia were diluted and plated onto CM + TRITON X-100 plates (from Union Carbide Chemicals,) and incubated at 28°C for -3 days. Colonies were replica plated and the replica plated plates were incubated at 28° C and 42° C. Putative temperature-sensitive mutants were picked and retested, then stored as a colony plug in 15% glycerol at -70 °C. The cells were replica plated and shifted to 42 °C for 24 hours. Strains that grew poorly or not at all were selected, because they were most likely to represent strains having a mutation in an essential gene. After 1 round of subjecting the collection of cells to the temperature shift, approximately 100 strains (10% of the strains) were identified as having failed to recover once they were shifted to the second permissive temperature. These 100 strains were again grown at a first permissive temperature, followed by 24 hours at 42 °C, and 24 or 48 hours at 28 °C (the second permissive temperature) . After this second round of selection, 10 strains were identified as having failed to recover, and therefore as containing a temperature sensitive mutation in an essential gene. Complementation analysis was used to identify the essential gene containing the mutation for each strain. Each of the 10 mutant strains was transformed, separately, with an Aspergillus genomic cosmid library containing an ArgB marker in a pCosAx vector (Adams et al . , FEMS Microbiol . Lett . , 122:227-231 1994). The strains were grown for 3-4 days at 28°C, replica plated, and shifted to 42 °C for a maximum of 3 days. Strains that grew were collected, and the cosmid DNA was packaged by "selfing" the organism to force it to undergo meiosis. In this method, a colony is picked and grown on a separate plate (which typically is sealed to prevent contamination) . The resulting spores then are picked and grown in liquid culture, prior to isolating the DNA. The cosmid was packaged using GIGAPACK III Gold packaging system (Stratagene; La Jolla, CA) , which produced plasmids that were subsequently isolated, purified, and used to transform bacteria for amplification, isolation, purification, and sequencing. In one of the resulting strains, the mutation was in a gene designated "AN97," indicating that in A . nidulans this gene is essential for survival. The amino acid sequence of the AN97 polypeptide and the AN97 gene of A . nidulans axe provided in Fig. 1 as SEQ ID NOs : 1 and 2, respectively. In a second strain, the mutation was in a gene designated "AN80," indicating that this gene is essential for survival. The AN80 amino acid and nucleic acid sequences are shown in Fig. 2 as SEQ ID NOs : 3 and 4, respectively. In a third strain, the mutation was in a gene designated "AN85," indicating that this gene is essential for survival. The AN85 amino acid and nucleic acid sequences are shown in Fig. 3 as SEQ ID NOs : 5 and 6, respectively. In a fourth strain, the mutation was in a gene designated "AN17," indicating that this gene is essential for survival. The AN17 amino acid and nucleic acid sequences are shown in Fig. 4 as SEQ ID NOs : 7 and 8, respectively. Now that each of these genes is known to be essential for survival of Aspergillus; the AN polypeptides (AN97, AN17, AN80, and AN85) can be used to identify antifungal agents by using the assays described herein. Other art-known assays to detect interactions of test compounds with proteins, or to detect inhibition of fungal growth also can be used with the AN97, AN17, AN80, and AN85 genes and gene products and homologs thereof .

Claims: Other Embodiments The invention also features fragments, variants, analogs, and derivatives of the AN polypeptides described above that retain one or more of the biological activities of the AN polypeptides, e.g., as determined in a complementation assay. Also included within the invention are naturally-occurring and non-naturally-occurring allelic variants. Compared with the naturally-occurring AN97, AN80, AN85, and AN17 nucleotide sequences depicted in Figs. 1, 2, 3, and 4 respectively, the nucleic acid sequence encoding allelic variants may have a substitution, deletion, or addition of one or more nucleotides. The preferred allelic variants are functionally equivalent to an AN polypeptide, e.g., as determined in a complementation assay. It is to be understood that, while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims. What is claimed is: 1. An isolated nucleic acid or an allelic variant thereof encoding : an AN97 polypeptide comprising the amino acid sequence of SEQ ID NO:l, as depicted in Fig. 1 ; an AN80 polypeptide comprising the amino acid sequence of SEQ ID NO:3, as depicted in Fig. 2 ; an AN85 polypeptide comprising the amino acid sequence of SEQ ID NO: 5, as depicted in Fig. 3; or an AN17 polypeptide comprising the amino acid sequence of SEQ ID NO: 7, as depicted in Fig. 4. 2. An isolated nucleic acid comprising a sequence selected from the group consisting of: (a) SEQ ID NO:2, as depicted in Fig. 1, or degenerate variants thereof; (b) SEQ ID NO: 2, or degenerate variants thereof, wherein T is replaced by U; (c) nucleic acids complementary to (a) and (b) ; (d) fragments of (a) , (b) , and (c) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO : 1 ; (e) SEQ ID N0:4, as depicted in Fig. 2, or degenerate variants thereof; (f) SEQ ID N0:4, or degenerate variants thereof, wherein T is replaced by U; (g) nucleic acids complementary to (e) and (f ) ; (h) fragments of (e) , (f) , and (g) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO : 3 ; (i) SEQ ID NO: 6, as depicted in Fig. 3, or degenerate variants thereof; (j) SEQ ID NO: 6, or degenerate variants thereof, wherein T is replaced by U; (k) nucleic acids complementary to (i) and (j); (1) fragments of (i) , (j), and (k) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO: 5 (m) SEQ ID NO: 8, as depicted in Fig. 4, or degenerate variants thereof; (n) SEQ ID NO: 8, or degenerate variants thereof, wherein T is replaced by U; (o) nucleic acids complementary to (m) and (n) ; and (p) fragments of (m) , (n) , and (o) that are at least 15 base pairs in length and which hybridize under stringent conditions to genomic DNA encoding the polypeptide of SEQ ID NO: 7. 3. An isolated nucleic acid from Aspergillus comprising a nucleotide sequence that is at least 85% identical to a nucleotide sequence selected from the group consisting of SEQ ID NO: 2, and encoding an AN97 polypeptide, SEQ ID NO: 4, and encoding an AN80 polypeptide, SEQ ID NO: 6, and encoding an AN85 polypeptide; and SEQ ID NO: 8, and encoding an AN17 polypeptide. 4. An isolated nucleic acid that is at least 15 base pairs in length and hybridizes under stringent conditions to a nucleotide sequence selected from the group consisting of SEQ ID NO: 2 SEQ ID NO: 4 SEQ ID NO: 6 and SEQ ID NO: 8 5. An isolated nucleic acid molecule, said molecule comprising the cDNA sequence contained within an American Type Culture Collection (ATCC) accession number selected from the group consisting of 209471, 209472, 209473, and 209484. 6. A vector comprising a nucleic acid of claim 1. 7. A vector comprising a nucleic acid of claim 2. 8. An expression vector comprising a nucleic acid of claim 1 operably linked to a nucleotide sequence regulatory element that controls expression of said nucleic acid. 9. An expression vector comprising a nucleic acid of claim 2 operably linked to a nucleotide sequence regulatory element that controls expression of said nucleic acid. 10. A genetically engineered host cell comprising a nucleic acid of claim 1. 11. A genetically engineered host cell comprising a nucleic acid of claim 2. 12. A host cell of claim 10, wherein the cell s a yeast or bacterium. 13. A host cell of claim 11, wherein the cell is a yeast or bacterium. 14. A genetically engineered host cell comprising a nucleic acid of claim 1 operably linked to a nucleotide sequence regulatory element that controls expression of the nucleic acid in the host cell . 15. A host cell of claim 14, wherein the cell is a yeast or bacterium. 16. A genetically engineered host cell comprising a nucleic acid of claim 2 operably linked to a nucleotide sequence regulatory element that controls expression of the nucleic acid in the host cell. 17. A host cell of claim 16, wherein the cell is a yeast or bacterium. 18. A polypeptide comprising an amino acid sequence selected from the group consisting of: the amino acid sequence of SEQ ID NO:l, as depicted in Fig. 1; the amino acid sequence of SEQ ID NO: 3, as depicted in Fig. 2; the amino acid sequence of SEQ ID NO: 5, as depicted in Fig . 3 ; and the amino acid sequence of SEQ ID NO: 7, as depicted in Fig. 4. 19. A polypeptide encoded by the cDNA sequence of the isolated nucleic acid molecule of claim 5. 20. A polypeptide encoded by a nucleic acid of claim 2. 21. A polypeptide encoded by a nucleic acid of claim 3. 22. A method for identifying an antifungal agent, the method comprising: (a) contacting an AN polypeptide with a test compound, wherein the AN polypeptide is selected from the group consisting of AN97, AN17, AN85, and AN80; (b) detecting binding of the test compound to the AN polypeptide; and (c) determining whether a test compound that binds to an AN polypeptide inhibits growth of fungi, relative to growth of fungi cultured in the absence of a test compound that binds to an AN polypeptide, wherein inhibition of growth is an indication that the test compound is an antifungal agent . 23. The method of claim 22, wherein the AN polypeptide is derived from a non-pathogenic Aspergillus strain. 24. The method of claim 22, wherein the AN polypeptide is derived from a pathogenic Aspergillus strain. 25. The method of claim 24, wherein the pathogenic Aspergillus strain is selected from the group consisting of Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger. 26. The method of claim 22, wherein the test compound is immobilized on a substrate, and binding of the test compound to the AN polypeptide is detected as immobilization of the AN polypeptide on the immobilized test compound. 27. The method of claim 26, wherein immobilization of the AN polypeptide on the test compound is detected in an immunoassay with an antibody that specifically binds to the AN polypeptide. 28. The method of claim 22, wherein the test compound is selected from the group consisting of polypeptides, ribonucleic acids, small molecules, and deoxyribonucleic acids. 29. The method of claim 28, wherein: (a) the AN polypeptide is provided as a fusion protein comprising the AN polypeptide fused to (i) a transcription activation domain of a transcription factor or (ii) a DNA- binding domain of a transcription factor; and (b) the test compound is a polypeptide that is provided as a fusion protein comprising the test polypeptide fused to (i) a transcription activation domain of a transcription factor or (ii) a DNA-binding domain of a transcription factor, to interact with the AN fusion polypeptide; and (c) binding of the test compound to the AN polypeptide is detected as reconstitution of a transcription factor. 30. A pharmaceutical formulation comprising an antifungal agent identified by the method of claim 22, and a pharmaceutically acceptable excipient. 31. A method for treating an organism having a fungal infection, the method comprising administering to the organism a therapeutically effective amount of the pharmaceutical formulation of claim 30. 32. A pharmaceutical formulation comprising an antifungal agent identified by the method of claim 24, and a pharmaceutically acceptable excipient. 33. A method for treating an Aspergillus infection in an organism, the method comprising administering to the organism a therapeutically effective amount of the pharmaceutical formulation of claim 32. 34. The method of claim 33, wherein the organism is a rodent or human. 35. The method of claim 33, wherein the organism is a plant . 36. An antibody that specifically binds to an AN polypeptide of claim 20. 37. An antibody of claim 36, wherein the antibody is a monoclonal antibody. 38. A pharmaceutical formulation comprising an antifungal agent, wherein the agent is a ribozyme that inhibits the function of AN97, AN17, AN80, or AN85. 39. A method for treating an organism having a fungal infection, the method comprising administering to the organism a therapeutically effective amount of the pharmaceutical formulation of claim 38. 40. A pharmaceutical formulation comprising an antifungal agent, wherein the agent is an antisense nucleic acid that inhibits the function of AN97, AN17, AN80, or AN85. 41. A method for treating an organism having a fungal infection, the method comprising administering to the organism a therapeutically effective amount of the pharmaceutical formulation of claim 40. 42. A method for identifying an antifungal agent, the method comprising: (a) contacting an AN polypeptide with a test compound, wherein the AN polypeptide is selected from the group consisting of AN97, AN17, AN85, and AN80; (b) detecting a decrease in function of the AN polypeptide contacted with the test compound; and (c) determining whether a test compound that decreases function of a contacted AN polypeptide inhibits growth of fungi, relative to growth of fungi cultured in the absence of a test compound that decreases function of a contacted AN polypeptide, wherein inhibition of growth is an indication that the test compound is an antifungal agent. 43. The method of claim 42, wherein the test compound is selected from the group consisting of polypeptides, ribonucleic acids, small molecules, and deoxyribonucleic acids. 44. The method of claim 42, wherein the test compound is an antisense oligonucleotide. 45. The method of claim 42, wherein the test compound is a ribozyme . 46. A method for identifying an antifungal agent, the method comprising: (a) contacting a nucleic acid encoding an AN polypeptide with a test compound, wherein the AN polypeptide is selected from the group consisting of AN97, AN17, AN80, and AN85; (b) detecting binding of the test compound to the nucleic acid; and (c) determining whether a test compound that binds the nucleic acid inhibits growth of fungi, relative to growth of fungi cultured in the absence of the test compound that binds the nucleic acid, wherein inhibition of growth is an indication that the test compound is an antifungal agent. 47. The method of claim 46, wherein the test compound is selected from the group consisting of polypeptides, small molecules, ribonucleic acids, and deoxyribonucleic acids. 48. The method of claim 46, wherein the test compound is an antisense oligonucleotide. 49. The method of claim 46, wherein the test compound is a ribozyme . 50. A method for identifying an anti-yeast agent, the method comprising: (a) contacting a yeast homolog of an AN polypeptide with a test compound, wherein the AN polypeptide is selected from the group consisting of AN97, AN17, AN85, and AN80; (b) detecting binding of the test compound to the yeast homolog; and (c) determining whether a test compound that binds to the yeast homolog inhibits growth of yeast, relative to growth of yeast cultured in the absence of the test compound that binds the yeast homolog, wherein inhibition of growth is indication that the test compound is an anti-yeast agent. 51. The method of claim 50, wherein the homolog is derived from a non-pathogenic yeast strain. 52. The method of claim 51, wherein the homolog is derived from Saccharomyces cerevisiae . 53. The method of claim 51, wherein the homolog is selected from the group consisting of D9798.4, L8543.16, YGROIOW, and L8004.2. 54. The method of claim 50, wherein the homolog is derived from a pathogenic yeast strain. 55. The method of claim 50, wherein the test compound is immobilized on a substrate, and binding of test compound to the homolog is detected as immobilization of the homolog on the immobilized test compound. 56. The method of claim 55, wherein immobilization of the homolog on the test compound is detected in an immunoassay with an antibody that specifically binds to the homolog. 57. The method of claim 50, wherein the test compound is selected from the group consisting of polypeptides, ribonucleic acids, small molecules, and deoxyribonucleic acids. 58. The method of claim 57, wherein: (a) the homolog is provided as a fusion protein comprising the homolog fused to (i) a transcription activation domain of a transcription factor or (ii) a DNA-binding domain of a transcription factor; and (b) the test compound is a polypeptide that is provided as a fusion protein comprising the test polypeptide fused to (i) a transcription activation domain of a transcription factor or (ii) a DNA-binding domain of a transcription factor, to interact with the homolog; and (c) binding of the test polypeptide to the homolog is detected as reconstitution of a transcription factor. 59. A method for identifying an anti-yeast agent, the method comprising: (a) contacting a homolog of an AN polypeptide with a test compound, wherein the AN polypeptide is selected from the group consisting of AN97, AN17, AN85, and AN80; (b) detecting a decrease in function of the AN polypeptide contacted by the homolog; and (c) determining whether a test compound that decreases function of a contacted AN polypeptide inhibits growth of yeast, relative to growth of yeast cultured in the absence of a test compound that decreases function of a contacted AN polypeptide, wherein inhibition of growth is an indication that the test compound is an anti-yeast agent. 60. The method of claim 59, wherein the test compound is selected from the group consisting of polypeptides, ribonucleic acids, small molecules, and deoxyribonucleic acids. 61. The method of claim 59, wherein the test compound is an antisense oligonucleotide. 62. The method of claim 59, wherein the test compound is a ribozyme . 63. A method for identifying an anti-yeast agent, the method comprising: (a) contacting a nucleic acid encoding a homolog of an AN polypeptide with a test compound, wherein the AN polypeptide is selected from the group consisting of AN97, AN17, AN80, and AN85; (b) detecting binding of the test compound to the nucleic acid; and (c) determining whether a test compound that binds the nucleic acid inhibits growth of yeast, relative to growth of yeast cultured in the absence of a test compound that binds the nucleic acid, wherein inhibition of growth is an indication that the test compound is an anti-yeast agent. 64. The method of claim 63, wherein the test compound is selected from the group consisting of polypeptides, small molecules, ribonucleic acids, and deoxyribonucleic acids. 65. The method of claim 63, wherein the test compound is an antisense oligonucleotide. 66. The method of claim 63, wherein the test compound is a ribozyme .

Inventors: GAVRIAS VICTORIA, KOLTIN YIGAL, GAVRIAS, VICTORIA, KOLTIN, YIGAL
Applicants: MILLENNIUM PHARM INC, MILLENNIUM PHARMACEUTICALS, INC.
Application year: 1998
Main classification: C12N15
IPC codes: A61K38, C07K14, C12N1, C12N15