Characterization of a Genetic Interaction Between SBP1 and WHI3 In Saccharyomyces cerevisiae

Proper regulation of cell cycle progression is necessary to ensure that cells do not undergo uncontrolled cellular division, which results in reduced cell volume, or cancer formation. The cell cycle is regulated by three checkpoints, the most important of which is the G1/S checkpoint. In the budding yeast S. cerevisiae, the G1/S checkpoint is sensitive to the levels of Cln3p, a homolog of mammalian cyclin D. To ensure that the cell passes through the G1/S checkpoint at the appropriate time, Cln3p levels throughout G1 phase are, in part, controlled by local translational repression of the CLN3 mRNA by Whi3p, an ER associated RNA binding protein, by an unknown mechanism. Previously, WHI3 was found to genetically interact with SBP1, a gene encoding an RNA binding protein involved in general translational repression. We characterized the genetic interaction between WHI3 and SBP1 by overexpressing Sbp1p in a whi3Δ strains. High Sbp1p overexpression in whi3Δ strains resulted in lethality at 37 C, whereas low overexpression resulted in a moderate growth defect at 30 C and a significant growth defect at 37 C. We next determined whether low Sbp1p overexpression could suppress the cell volume defect in whi3Δ strains, by calculating budding cell volume of mid‐log phase cultures grown at 30 C and 37 C. whi3Δ cells overexpressing Sbp1p were significantly larger at 37 C than whi3Δ cells whereas there was no effect at 30 C.