Association of Chk1 with 14-3-3 proteins is stimulated by DNA damage

The protein kinase Chk1 is required for cell cycle arrest in response to DN A damage. We have found that the 14-3-3 proteins Rad24 and Rad25 physically interact with Chk1 in fission yeast. Association of Chk1 with 14-3-3 prote ins is stimulated in response to DNA damage. DNA damage results in phosphor ylation of Chk1 and the 14-3-3 proteins bind preferentially to the phosphor ylated form. Genetic analysis has independently implicated both Rad24 and R ad25 in the DNA-damage checkpoint pathway. We suggest that DNA damage-depen dent association of phosphorylated Chk1 with 14-3-3 proteins mediates an im portant step along the DNA-damage checkpoint pathway, perhaps by directing Chk1 to a particular substrate or to a particular location within the cell. An additional role for 14-3-3 proteins in the DNA-damage checkpoint has be en suggested based on the observation that human Chk1 can phosphorylate Cdc 25C in vitro creating a 14-3-3 binding site. Our results suggest that in fi ssion yeast the interaction between the 14-3-3 proteins and Cdc25 does not require Chk1 function and is unaffected by DNA damage, in sharp contrast to the interaction between the 14-3-3 proteins and Chk1.