Principal Investigator/Program Director (Last, first, middle): Haye, Joanna, Elizabeth Abstract: DNA mismatch repair (MMR) is a highly conserved process. A functional MMR pathway is essential for maintaining genome integrity; loss of MMR results in genome instability and cancer in higher eukaryotes. For example, defects in MMR genes result in Lynch Syndrome, a common hereditary cancer syndrome resulting in early onset cancers of the colon, endometrium, ovaries, small intestine, hepatobiliary tract, upper urinary tract as well as other tissues. In our most recent publication, we showed that in yeast, deletion of Modulator of Transcription (also known as Not4) or General Control Nonderepressible 5 (Gcn5) modulate the levels of Msh2, a major MMR component. Loss of Gcn5 significantly decreases Msh2, whereas deleting Not4 stabilizes functional Msh2. Not4 and Gcn5 are proteins that ubiquitylate and acetylate various proteins respectively. We hypothesize that Not4 and Gcn5 modify yeast MutSα (comprised of Ms2 and Msh6) and that the modifications affect the stability of the complex. Using the yeast Saccharomyces cerevisiae (S. cerevisiae), the first aim of the proposed research is to establish the role of Gcn5 and Not4 in the regulation of the major mismatch recognition complex MutSα. Our previous experiments have also shown that yeast MutS tracks with the replication machinery during DNA replication. Human MutSα is recruited to chromatin through specific histone modifications and interacts with the replication machinery by binding PCNA, the DNA polymerase processivity factor. However, the modifications that recruit human MutSα are not utilized in yeast. How yeast MutSα is recruited to chromatin remains elusive. The second aim of this research is to determine the role of post- translational modifications in MutSα recruitment to chromatin. PHS398 (Rev. 5/01) Page Continuation Format Page