Multiple DNA repair pathways contribute to cell lethality in checkpoint mutants

Abstract

The checkpoint kinases Mec1 and Rad53 play an essential role in stabilizing stalled DNA replication forks. We have initiated a genetic screen to identify mutants that render checkpoint-defective yeast cells more resistant to fork-stalling agents (e.g. hydroxyurea, MMS, etc). We have screened the entire 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. We have also found that there is a significant Increase in HU-resistance when combining different repair mutants in rad53-null background. However, none of these multiple mutants is able to rescue viability completely, indicating that there are other requirements to maintain fork stability in the absence of rad53.