PROJECT SUMMARY Toxoplasma gondii is an intracellular protozoan parasite that poses a major threat to patients with HIV/AIDS. The replicative stage (tachyzoite) develops into a latent stage (bradyzoite) that resides inside host cells as cysts in brain, heart, and skeletal muscle tissues. Tissue cysts remain in the host for life, as they are impervious to the immune response and currently approved drugs, and give rise to recurrent reactivation of infection in immune compromised patients. Despite its clinical importance, little is known about the complex transition from the tachyzoite to bradyzoite stage. A key transcription factor called BFD1 was recently discovered that is necessary and sufficient for cyst formation in vitro and in mice, but we currently know nothing about the regulation this factor. We will fill this gap in our knowledge building from our strong preliminary findings that BFD1 is subject to tight regulatory control at the post- transcriptional level. We have shown that translation of BFD1 mRNA is enhanced more than 30- fold in response to TgIF2α phosphorylation. Consistent with this observation is the presence of numerous upstream open reading frames (uORFs) in the 5’-leader of BFD1 mRNA. Aim 1 will test our hypothesis that these uORFs play a key role in the preferential translation of BFD1 that occurs in response to bradyzoite induction. In addition to translational control, we have additional preliminary data suggesting that BFD1 is regulated at the protein level through lysine acetylation. Our acetylome analysis of tachyzoites found that BFD1 is acetylated at lysine 1720 (K1720) and that BFD1 was the top hit in a yeast two-hybrid screen performed with the lysine acetyltransferase TgGCN5a. Aim 2 will test our hypothesis that TgGCN5a regulates BFD1 through K1720 acetylation using co-immunoprecipitation assays and mutational analysis. Completion of these two aims will reveal critical new insights into the post-transcriptional mechanisms that govern BFD1 activity, which promise to serve as novel points of therapeutic intervention to treat this devastating opportunistic infection in HIV/AIDS patients.