The GIN4 Family Kinase, Cdr2p, Acts Independently of Septins in Fission Yeast

Two relatives of the GIN4 protein kinase family, Cdr1p and Cdr2p, exist in the yeast Schizosaccharomyces pombe. Although in Saccharomyces cerevisiae GIN4-related kinases influence septin ring organization and septin rings influence the localization and function of GIN4-related protein kinases, it is unknown whether this relationship is conserved in S. pombe. Here, we have probed the relationship between Cdr2p activity and septins and find that Cdr2p and septins are functionally independent. Cdr2p localizes in a cortical band overlying the nucleus during interphase, whose dimension is proportional to cell length, and to a medial ring structure in late mitosis. Both localizations are septin-independent and disrupted by treatment with filipin. Structure/function analysis indicates that the intracellular targeting domain of Cdr2p is largely contained within its non-catalytic C-terminus. Cdr2 protein kinase activity, while unimportant for its localization, is critical for its cell cycle function. Our data indicate that Cdr2p functions at two positions within the cell at discrete cell cycle stages to influence the timing of mitotic entry and cytokinesis, respectively.