Cell cycle control of spindle pole body duplication and splitting by Sfi1 and Cdc31 in fission yeast

Spindle pole biogenesis and segregation are tightly coordinated to produce a bipolar mitotic spindle. In yeasts, the spindle pole body (SPB) half‐bridge composed of Sfi1 and Cdc31 duplicates to promote the biogenesis of a second SPB. Sfi1 accumulates at the half‐bridge in two phases in Schizosaccharomyces pombe , from anaphase to early septation and throughout G2 phase. We found that the function of Sfi1–Cdc31 in SPB duplication is accomplished before septation ends and G2 accumulation starts. Thus, Sfi1 early accumulation at mitotic exit might correspond to half‐bridge duplication. We further show that Cdc31 phosphorylation on serine 15 in a Cdk1 (encoded by cdc2 ) consensus site is required for the dissociation of a significant pool of Sfi1 from the bridge and timely segregation of SPBs at mitotic onset. This suggests that the Cdc31 N‐terminus modulates the stability of Sfi1–Cdc31 arrays in fission yeast, and impacts on the timing of establishment of spindle bipolarity.