ATR-Dependent Activation of S-Phase Checkpoint: The Influence of Replication Stress Severity and Duration on Cdc6 Mediation

Abstract

The CDC6 protein is well-known to facilitate replication origin activation in eukaryotic cells. The Cdc6 protein is part of the pre-replication complex, which initiates DNA replication by binding to specific sites on the genome called origins of replication. In doing so, it helps recruit other proteins that are required for DNA synthesis. It is also an important factor in response to replication stress, where it has been shown to physically interact with ATR in order to activate the S-phase checkpoint response. The ATR, though, can also activate the S-phase checkpoint without interacting with Cdc6. Up to this day, the Cdc6-ATR binding was thought occur where there is a low level of replication stress. Here we show that it can also occur when high levels of replication stress persist for long time. Our research shows that in root meristem cells of V. faba, subjected to long-term replication stress (24–32 hours) induced by hydroxyurea, some DNA damage sites express ATR activity through binding with Cdc6. We conclude that the Cdc6-ATR cooperation may not only depend on the dose of the stressor but also on the longitude of the treatment.