Phosphosites of the yeast centrosome component Spc110 contribute to cell cycle progression and mitotic exit

Spc110 is an essential component of the spindle pole body (SPB), the yeast equivalent of the centrosome, that recruits the γ-tubulin complex to the nuclear side of the SPB to produce the microtubules that form the mitotic spindle. Here we identified phosphosites S11 and S36 in maternally originated Spc110 and explored their functions in vivo. Yeast expressing non-phosphorylatable Spc110S11A had a distinct spindle phenotype characterized by higher levels of α-tubulin, which was frequently asymmetrically distributed between the two SPBs. Furthermore, expression of the double mutant Spc110S11AS36A had a delayed cell cycle progression. Specifically, the final steps of mitosis were delayed in Spc110S11AS36A cells, including expression and degradation of the mitotic cyclin Clb2, disassembling the mitotic spindle and re-localizing Cdc14 to the nucleoli, resulting in late mitotic exit and entry in G1. Thus, we propose that Spc110 phosphorylation at S11 and S36 is required to regulate timely cell cycle progression in budding yeast.