Mitochondrial regulation in Cryptococcus neoformans Cryptococcus neoformans is a global pathogen responsible for hundreds of thousands of deaths yearly in HIV+ individuals and increasing morbidity in non-AIDS patient populations.  Mitochondrial processes are central to multiple aspects of cryptococcal biology and pathogenesis, and mitochondrial morphology correlates with the virulence of clinical strains within this species complex.  Despite this, mitochondria have been have been ne- glected as potential targets for therapies to combat this devastating AIDS-related pathogen.  The goal of this research is to address this gap in knowledge by determining how C. neoformans regulates key mitochondrial metabolic processes and morphological transitions, both of which are required for normal virulence.  Based on the literature and strong preliminary data, we specifically propose to explore the mitochondrial regulator Ssn801.  We hypothesize that this protein acts both as a transcriptional regulator in the nucleus and as an ef- fector protein at the mitochondria to influence mitochondrial function and morphology; through these activities it modulates the resistance of C. neoformans to host-imposed stress, and thus its virulence.  We propose to apply complementary approaches of genomics and biochemistry to test this hypothesis and define mechanisms of mitochondrial regulation.  In Aim 1 we will use gene expression analysis to determine the targets of Ssn801 and its associated kinase under conditions of host-like stress.  In Aim 2 we will use microscopy and protein in- teraction methods to determine the subcellular distribution of Ssn801 and its physical targets, thereby elucidat- ing its mechanism of action.  Completing the proposed studies will reveal how Ssn801 regulates C. neoformans mitochondrial function and morphology and will highlight features of cryptococcal biology that are distinct from those of host cells.  The significance of this application lies in the impact of the pathogen on human health, especially for AIDS patients; the importance of defining mitochondrial regulation in C. neoformans; the likely new insights into basic biology to be gained, which may apply to other microbes; the data resources to be provided to the community; and the potential for future application in terms of identifying novel therapeutic targets.  The innovation of the proposal lies in its focus on mechanistic understanding of mitochondrial regulation and remodeling in an important fun- gal pathogen, and its combination of approaches.  The probability of success of this exploratory proposal is high, as is its potential impact in terms of basic understanding, identification of potential vulnerabilities of the system that might be exploited in the future, and new directions for follow-up by us and others.