CHARACTERIZATION OF THE COHESIN ACETYLTRANSFERASE ECO1 AND ITS ROLE IN NUCLEAR FUNCTIONS

Abstract

Sister-chromatid cohesion plays a vital role in precise chromosome segregation and genome stability. This process is carried out by the cohesin complex and its associated proteins. In addition, a growing body of evidence suggests that the cohesin complex affects other processes, including gene transcription, DNA damage repair, and DNA replication. One piece of evidence for cohesin's role in other processes is that individuals with mutations in the cohesin complex can survive, albeit with congenital abnormalities. For example, mutations in ESCO2 cause Roberts syndrome. ESCO2 is the human homolog of Eco1 in budding yeast. Eco1 is a critical acetyltransferase for establishing cohesion during S phase and also re-establishing cohesion in G2/M phase in response to DNA damage. To identify the roles of the cohesin complex beyond chromosome segregation, we have constructed mutations in Eco1 which do not cause gross chromosome separation defect. We have shown that DNA damage repair is strongly affected in the eco1 mutants and that a specific DNA recombination pathway is affected. Further investigation of eco1 mutants showed transcription and DNA replication defects genome-wide. Interestingly, deletion of Fob1, a nucleolar protein required for replication fork blocking in rDNA region, corrects the genome-wide replication defects, nucleolar structure and chromosome segregation in an eco1 mutant by allowing bidirectional replication of the rDNA. This highlights cohesin's central role at the rDNA for global control of DNA replication and gene expression. Our results demonstrate the diversity of cohesin functions and have direct implications for the etiology of human cohesinopathies.