Anillin/Mid1p interacts with the ECSRT-associated protein Vps4p and mitotic kinases to regulate cytokinesis in fission yeast

Cytokinesis is the final stage of the cell cycle which separates cellular constituents to produce two daughter cells. Using Schizosaccharomyces pombe we have investigated the role of various classes of proteins involved in this process. Central to these is anillin/Mid1p which forms a ring-like structure at the cell equator that predicts the site of cell separation through septation in fission yeast. Here we demonstrate a direct physical interaction between Mid1p and the endosomal sorting complex required for transport (ESCRT)-associated protein Vps4p. The interaction is essential for cell viability, and Vps4p is required for the correct cellular localization of Mid1p. Furthermore, we show that Mid1p is phosphorylated by the aurora kinase Aurora A, that the interaction of mid1 and ark1 genes is essential for cell viability, and that Ark1p is also required for the correct cellular localization of Mid1p. We mapped the sites of phosphorylation of Mid1p by Aurora A and the polo kinase Plk1 and assessed their importance by mutational analysis. Mutational analysis revealed S332, S523 and S531 to be required for Mid1p function and its interaction with Vps4p, Ark1p and Plo1p. Combined our data suggest a physical interaction between Mip1p and Vps4p important for cytokinesis, and identify phosphorylation of Mid1p by aurora and polo kinases as being significant for this process.