14-3-3 proteins regulate exonuclease 1-dependent processing of stalled replication forks

Replication fork integrity,which is essential for the maintenance of genome stability,is monitored by checkpoint-mediated phosphorylation events. 14-3-3 proteins are able to bind phosphorylated proteins and were shown to play an undefined role under dna replication stress. exonuclease 1 (exo1) processes stalled replication forks in checkpoint-defective yeast cells. we now identify 14-3-3 proteins as in vivo interaction partners of exo1,both in yeast and mammalian cells. yeast 14-3-3-deficient cells fail to induce mec1-dependent exo1 hyperphosphorylation and accumulate exo1-dependent ssdna gaps at stalled forks,as revealed by electron microscopy. this leads to persistent checkpoint activation and exacerbated recovery defects. moreover,using dna bi-dimensional electrophoresis,we show that 14-3-3 proteins promote fork progression under limiting nucleotide concentrations. we propose that 14-3-3 proteins assist in controlling the phosphorylation status of exo1 and additional unknown targets,promoting fork progression,stability,and restart in response to dna replication stress. © 2011 engels et al.