|M.Sc Student||Karni Shiri|
|Subject||The Switch from Repression to Transcriptional Activation|
of Early Meiosis Specific Genes in S.Cerevisiae
|Department||Department of Biology||Supervisor||Professor Emeritus Yona Kassir|
Early meiosis- specific genes are silent in a media promoting vegetative growth with glucose as the sole carbon source due to the formation of repression complexes on their promoters. Ume6, a DNA binding protein that binds to the promoter of these genes, recruits Sin3/Rpd3- the histone deacetylase complex, and Isw2- the chromatin remodeling complex. Under meiotic conditions, i.e. nitrogen depletion in the presence of acetate as the sole carbon source, Ume6 recruits the meiosis specific transcriptional activator, Ime1. In addition, Gcn5, a histone acetylase is also required for the transcription of these genes. In my thesis I tried to understand why under meiotic conditions the Isw2 complex doesn't repress the transcription of EMGs. I found that Isw2 is present throughout the meiotic process. A repression test revealed that Isw2 represses transcription only in the presence of glucose, and that this repression is partially dependent on Rim11, and is completely dependent on Rim15. The presence of Rim15 protein rather than its function as a kinase is required. The second aim of my thesis was to understand how Gcn5, a histone acetyl transferease, activates the transcription of EMGs. I found that Isw2, similarly to Gcn5, is also present throughout the meiotic pathway. Deletion of GCN5 has no effect on spore formation or viability, but the transcription of early and middle meiotic genes, as well as premeiotic DNA replication was delayed. On the other hand, a point mutation in the catalytic domain of Gcn5 has a more severe effect, cells arrest in G1 prior to the transcription of meiosis-specific genes, and spores are not formed.