Phospho-Regulation of the Anillin-Related Scaffolding Protein Mid1 by Sid2 in Fission Yeast Cytokinesis

During cytokinesis, division of one cell into two identical cells occurs through constriction of a protein-rich ring structure: the contractile ring. In fission yeast, the protein Mid1 functions as a scaffold to bridge the cell cortex with the contractile ring. Coincident with its cortical accumulation, Mid1 becomes hyper-phosphorylated. Mass spectroscopy and two-dimensional phosphopeptide mapping identified multiple Sid2 phosphorylation sites within Mid1. Phospho-site mutants were generated at the endogenous mid1 locus and analyzed. These cells displayed cell division defects, including sensitivity to low dose latrunculin A and disorganized actin localization. Also, Mid1 protein levels increased when compared to checkpoint activated cells expressing wild-type Mid1. Given that Mid1 departure from the contractile ring coincides with Sid2 relocalization to the division site, Sid2 may temporally regulate the interaction of Mid1 with the membrane or other contractile ring components