THE RCK1 AND RCK2 PROTEIN-KINASE GENES FROM SACCHAROMYCES-CEREVISIAE SUPPRESS CELL-CYCLE CHECKPOINT MUTATIONS IN SCHIZOSACCHAROMYCES-POMBE

The protein kinase-encoding genes RCK1 and RCK2 from Saccharomyces cer evisiae have been identified as suppressors of Schizosaccharomyces pom be cell cycle checkpoint mutations. Upon expression of these genes, ra diation resistance is partially restored in S. pombe mutants with chec kpoint deficiencies, but not in mutants with DNA repair defects. Some checkpoint mutants are sensitive to the DNA synthesis inhibitor hydrox yurea, and this sensitivity is also suppressed by RCK1 and RCK2. The d egree of suppression can be modulated by varying expression levels. Ex pression of RCK1 or RCK2 in S. pombe causes cell elongation and decele rated growth. Cells expressing these genes have a single nucleus and a 2n DNA content. We conclude that these genes act in S. pombe to prolo ng the G2 phase of the cell cycle.