P13(SUC1) OF SCHIZOSACCHAROMYCES-POMBE REGULATES 2 DISTINCT FORMS OF THE MITOTIC CDC2 KINASE

suc1 is an essential gene initially identified for its ability to resc ue certain temperature-sensitive alleles of cdc2 in Schizosaccharomyce s pombe. The role of suc1 in the regulation of the cdc2 kinase is not well understood. In our study, we have characterized the biochemical e ffect of loss of suc1 function on specific cdc2-cyclin complexes. We s how that the cig1 cyclin is associated with cdc2 and that the cdc2-cig 1 kinase is activated at mitosis, with kinetics similar to those of th e cdc2-cdc13 kinase. We provide evidence that loss of suc1 function af fects the kinase activity of the two distinct mitotic forms of the cdc ? kinase. We also show that a dramatic increase in the level of the cd c13 protein is associated with loss of suc1. These results suggest tha t mitosis cannot be properly completed in the absence of suc1, possibl y because of an increase in the level of cdc2-cdc13 complex, and suppo rt the idea of a role for suc1 in the regulation of multiple forms of the cdc2 kinase.