Fungal diseases in humans are extremely common. They include mild cosmetic symptoms, recurrent skin and mucosal surface infections, and the rarer life-threatening diseases caused by disseminated fungi particularly in immunocompromised patients such as those suffering from AIDS, undergoing chemotherapy or corticosteroid therapy, and organ transplant recipients. Currently there is a limited repertoire of drugs available to treat fungi. Some species are naturally resistance to these drugs and resistance can be acquired in clinical settings. Thus, there is an urgent need to develop new treatments for fungal diseases. The objective of this proposal is to identify suitable targets for drug development in fungi, using a model organism Cryptococcus neoformans (in phylum Basidiomycota). This fungus is very diverged and different from commonly studied pathogenic or model species like Candida albicans, Saccharomyces cerevisiae or Schizosaccharomyces pombe (in phylum Ascomycota), and thus discoveries made in this organism are expected to extend across all pathogenic fungi. The specific aim of the proposed research is to identify essential genes of C. neoformans, using two experimental approaches. Essential genes are those required for viability: because mutants cannot grow, the identification of essential genes is a technical challenge. Here these genes will be identified by an innovative genetic screen and through a bioinformatic prioritization to essential genes found in fungi but not in humans. The proposal will also generate a resource of heterozygous strains suitable for small molecule studies utilizing haplo-insufficiency. The discovery of these essential genes represents new avenues for the development of antifungal agents.