Genetic and Molecular Analysis of cdrl lniml in Schizosacchuromyces Pombe

The cdrl gene in Schizosaccharomyces pombe was identified as a mutation affecting the nutritional responsiveness of the mitotic size control. cdrl alleles have been further analyzed for genetic interactions with elements of :he mitotic control pathway and cloned by plasmid rescue of a conditional lethal cdrl-76 cdc25-22 double mutant. These analyses show that the cdrl gene is allelic to niml, a gene identified as a high copy number plasmid suppressor of the mitotic control gene, cdc25. The gene structure for cdrl differs from the described niml gene in the carboxyl-terminal portion of the gene. The published niml sequence encoded a product of predicted M, 45,000, and included 356 amino acids from the amino-terminal region of the gene and 14 amino acids from a noncontiguous carboxyl-terminal fragment. The cdrl sequence includes an additional 237 amino acids of the contiguous fragment and encodes a product of predicted M, 67,000. The sequence shows a high level of identity with protein kinases over the amino-terminal catalytic domain, and limited identity with yeast protein kinases SNFl, KIN2 and KIN1 over part of the carboxyl-terminal domain. The effect of overexpression of the full length gene has been examined in various genetic backgrounds. These data show that the full length gene product is required to give a normal cell cycle response to nitrogen starvation. A detailed examination of the genetic interaction of cdrl mutants with various mutants of mitotic control genes (cdc2, cdc25, weel, cdcl3) demonstrated strong interactions with cdc25, some cdc2 alleles, and with cdcl3-117. Overall, the results are interpretable within the framework of the existing model of cdrllniml action in mitotic control, i.e., cdrl functions upstream of weel to relieve mitotic inhibition.