Characterization of Byr4 and Cdc7 functional domains affecting the septation initiation network in Schizosaccharomyces pombe

Abstract

The study of cytokinesis in fission yeast S.pombe has revealed a signaling network, the septation initiation network (SIN) that serves to coordinate cytokinesis with mitotic exit in the fission yeast Schizosaccharomyces pombe. The timing of cytokinesis and septum formation hinges upon the activation of the GTPase Spg1. Given the central role of Spg1 GTPase in regulating this pathway we investigated the role of Cdc7 its effector, and Byr4 the GAP component that serves to inactivate it. In order to elucidate Cdc7 regulation I have identified various functional domains within Cdc7. I show that a region adjacent to the kinase domain is responsible for association with Spg1 but insufficient for SPB localization. In addition I find that Cdc7 self associates which is required for binding to Spg1. Our findings indicate that there are potentially multiple modes of regulating Cdc7 function and hence the SIN. I have investigated the regulation of the GAP component Byr4 by phosphorylation as a means of regulating Spg1activation and further characterized its interaction with Spg1 and Cdc16. Together these results point to modes of regulating the activation of Spg1 and its effector as a means of controlling septum formation and cytokinesis.