THE CDC7 PROTEIN-KINASE IS A DOSAGE-DEPENDENT REGULATOR OF SEPTUM FORMATION IN FISSION YEAST

Mutation of the Schizosaccharomyces pombe cdc7 gene prevents formation of the division septum and cytokinesis, We have cloned the cdc7 gene and show that it encodes a protein kinase which is essential for cell division. In the absence of cdc7 function, spore germination, DNA synt hesis and mitosis are unaffected, but cells are unable to initiate for mation of the division septum. Overexpression of p120(cdc7) causes cel l cycle arrest; cells complete mitosis and then undergo multiple round s of septum formation without cell cleavage, This phenotype, which is similar to that resulting from inactivation of cdc16 protein, requires the kinase activity of p120(cdc7). Mutations inactivating the early s eptation gene, cdc11, suppress the formation of multiple septa and all ow cells to proliferate normally. If formation of the division septum is prevented by inactivation of either cdc14 or cdc15, p120(cdc7) over production does not interfere with other events in the mitotic cell cy cle. Septation is not induced by overexpression of p120(cdc7) in G(2) arrested cells, indicating that it does not bypass the normal dependen cy of septation upon initiation of mitosis. These findings indicate th at the p120(cdc7) protein kinase plays a key role in initiation of sep tum formation and cytokinesis in fission yeast and suggest that p120(c dc7) interacts with the cdc11 protein in the control of septation.