Scw1p Antagonizes the Septation Initiation Network To Regulate Septum Formation and Cell Separation in the Fission Yeast Schizosaccharomyces pombe

Cytokinesis in the fission yeast Schizosaccharomyces pombe is regulated by a signaling pathway termed the septation initiation network (SIN). The SIN is essential for initiation of actomyosin ring constriction and septum formation. In a screen to search for mutations that can rescue the sid2-250 SIN mutant, we obtained scw1-18. Both the scw1-18 mutant and the scw1 deletion mutant (scw1Delta mutant), have defects in cell separation. Both the scw1-18 and scw1Delta mutations rescue the growth defects of not just the sid2-250 mutant but also the other temperature-sensitive SIN mutants. Other cytokinesis mutants, such as those defective for actomyosin ring formation, are not rescued by scw1Delta. scw1Delta does not seem to rescue the SIN by restoring SIN signaling defects. However, scw1Delta may function downstream of the SIN to promote septum formation, since scw1Delta can rescue the septum formation defects of the cps1-191beta-1,3-glucan synthase mutant, which is required for synthesis of the primary septum.