The role and regulation of Rif1 as an anti-checkpoint protein in S. cerevisiae

Abstract

The response to DNA damage is imperative to deciding the future of a cell. Damage needs to be repaired before the cell cycle is allowed to continue, or the cell must be destroyed. We study the role of the budding yeast telomeric protein Rif1 during arrest of the cell cycle, primarily in the temperature sensitive cdc13-1 strains, which undergoes telomere uncapping and DNA strand resection. Rap-interacting factor 1 (Rif1) forms a complex with Rap1 and Rif2 to antagonise the action of telomerase at telomeres. Rif1 has since been shown to be conserved across eukaryotes, with roles in a number of processes such as a globally conserved role in regulation of replication timing, and repair pathway choice at mammalian double strand breaks. We further develop an observed anti-checkpoint role of Rif1 during telomere uncapping, which correlates to a cell cycle arrest dependent phosphorylation of Rif1. In this we have demonstrated the likely phosphorylation sites of Rif1 during cell cycle arrest, as well as the importance of these sites for this anti-checkpoint role. Through substitution of these amino acid residues we have demonstrated that cdc13-1 strains containing non-phosphorylated Rif1 protein show increased sickness. We have further demonstrated that this phosphorylation is downstream of the activity of the CDK1 equivalent, Cdc28, and also occurs in cell cycle arrest resulting from multiple arresting reagents. We propose that Rif1 binds to regions of resected DNA and thereby shields ssDNA from recognition by checkpoint proteins, and that this interaction is regulated by the addition of phosphoryl groups at Serine-57 and Serine-110. The potentially conserved nature of this interaction could impact studies on RIF1 in human cells.