Asf1 links Rad53 to control of chromatin assembly

Yeast defective in the checkpoint kinase Rad53 fail to recover from transient DNA replication blocks and synthesize intact chromosomes. The effecters of Rad53 relevant to this recovery process are unknown. Here we report that overproduction of the chromatin assembly factor Asf1 can suppress the Ts phenotype of mrc1rad53 double mutants and the HU sensitivity of rad53 mutants. Eliminating silencing also suppresses this lethality, further implicating chromatin structure in checkpoint function. We find that Asf1 and Rad53 exist in a dynamic complex that dissociates in response to replication blocks and DNA damage. Thus, checkpoint pathways directly regulate chromatin assembly to promote survival in response to DNA damage and replication blocks.