Degradation of budding yeast protein Far1 during G1/S phase transition

Abstract

Cell cycle events must be precisely controlled for the cell to proliferate. Cyclin-dependent kinases (Cdks) upon activation by cyclins control cell cycle events. Cyclin-Cdk complexes govern events of cell cycle by binding their substrate proteins at specific docking motifs and phosphorylating them, thus changing the proteins’ activity. Far1 is a cyclin-dependent kinase inhibitor, that causes cell cycle arrest in response to mating pheromones. However, if mating pheromones are not present, Far1 is degraded. Clb5-Cdk1 complex phosphorylates the protein at S87/S91 residues, which triggers Far1 degradation. A Clb5-Cdk1 docking motif in N-terminal part of Far1 was recently discovered. This sequence, however, serves as docking motif only in truncated NFar1(1-170 aa). In this work it was shown that another possible motif involved in Far1 degradation might be located between 170th and 190th amino acids in the protein, Far1 does not contain another degron besides S87/S91 and Pho85 kinase does not affect Far1 degradation.