This proposal describes experiments to investigate the regulation of meiosis-specific target genes in yeast. This research has initially focused on the transcriptional regulation of HOP1, a gene expressed early in the meiotic pathway. The URS1H site in the HOP1 promoter is bound by the Ume6 protein and functions as a repressor during mitosis and an activator during the early stages of meiosis. However, Ume6 also binds to URS1 sites in non-meiotic promoters to regulate transcription. This raises the question of how the cell distinguishes between Ume6 bound to meiotic and non-meiotic promoters to differentially regulate genes. One of the objectives is to identify the proteins that bind to URS1 and determine how they contribute to the specificity of meiotic induction. To investigate the mechanisms that control transcription of genes expressed later in the meiotic pathway, the regulation of SMK1, a mid-sporulation specific MAP kinase required for spore development, has been examined. A regulatory site in the SMK1 promoter called MSE has been identified, which function to repress transcription during vegetative growth and the early stages of meiosis and activate transcription during middle stages of meiosis. This site sets the timing of SMK1 expression. The Ndt80 protein binds to this site to activate transcription during meiosis. Preliminary studies have shown the Sum1 and Hst1 proteins are required for MSE-mediated repression and that Sum1 protein binds to the site. Interestingly, these proteins have previously been identified based upon their sequence or functional similarity to proteins involved in transcriptional silencing of the mating type, telomeres, and rDNA loci. However, unlike silencing proteins, Sum1 and Hst1 are gene-specific regulation and therefore may function by a novel mechanism. Experiments are proposed to investigate the interactions and mechanisms of DNA binding of Sum1 and Hst1, potentially novel DNA binding proteins. The mechanism by which Sum1 and Hst1 repress transcription will be investigated. Additionally, the regulation of Sum1 and Hst1 activity by the meiotic regulatory pathway will be examined.
