The role of the Sid1p kinase and Cdc14p in regulating the onset of cytokinesis in fission yeast

Coordination of mitosis and cytokinesis is crucial for ensuring proper chro mosome segregation and genomic stability. In Schizosaccharomyces pombe, the sid genes (cdc7, cdc11, cdc14, spg1, sid1, sid2 and sid4) define a signali ng pathway that regulates septation and cytokinesis. Here we describe the c haracterization of a novel protein kinase, Sid1p, Sid1p localizes asymmetri cally to one spindle pole body (SPB) in anaphase. Sid1p localization is mai ntained during medial ring constriction and septum synthesis and disappears prior to cell separation. Additionally, we found that Cdc14p is in a compl ex with Sid1p. Epistasis analysis places Sid1p-Cdc14p downstream of Spg1p-C dc7p but upstream of Sid2p, Finally, we show that cyclin proteolysis during mitosis is unaffected by inactivating the sid pathway; in fact, loss of Cd c2-cyclin activity promotes Sid1p-Cdc14p association with the SPB, possibly providing a mechanism that couples cytokinesis with mitotic exit.