Different repair pathways are involved in checkpoint-dependent replication fork stabilization

Abstract

The ability to survive spontaneous and induced DNA damage depends on S phase checkpoints, which act by inhibiting late origin firing, stabilizing replication forks and preventing S phase progression. It has been previously shown in our lab that the preservation of fork integrity, rather than inhibition of origin firing, is essential to mantain cell viability under DNA damage conditions. Therefore, we are interested in the identification of checkpoint-dependent pathways involved in stabilization of the forks. We have initiated a genetic screen to identify mutants that render checkpoint-defective yeast cells more resistant to fork-stalling agents. In our first attempt we identified a number of mutants but we were unable to complement the mutants because of the partially penetrant phenotype. We have screened the entire deletion library for mutants with heightened resistance to hydroxyurea when the checkpoint has been compromised with caffeine. From this, we have identified mutants in several repair pathways, and therefore, we decided to check for caffeine plus hydroxyurea resistance in several members of the main repair pathways. Our conclusions indicate that different repair pathways contribute to lethality in checkpoint mutants.