The balance between ATR and DDK activities controls TopBP1-mediated locking of dormant origins at the pre-IC stage

Abstract

SummaryReplication stress, a major hallmark of cancers, and ensuing genome instability source from impaired progression of replication forks. The first line of defense against fork slowing is compensation, a long-described process that elicits firing of otherwise dormant origins. It remains unclear whether compensation requires activation of the DNA replication checkpoint or passively results from lengthening of the window of time during which dormant origins can fire when fork progression slows, or both. Using molecular DNA combing we show here that a linear relationship ties inter-origin distances to fork speeds, independently of the checkpoint status. We called this line “stressline” and further show that its slope enables precise quantification of the compensation efficiency. Comparison of the slopes in different genetic backgrounds reveals that compensation requires ATR, not CHK1, while TopBP1 and CDC7/DBF4 repress dormant origin activation. These results strongly suggest that TopBP1 locks dormant origins at the pre-IC stage and that ATR and DDK oppose to control the conversion of dormant pre-ICs into functional salvage origins. Both passive and active processes thus contribute to compensation. Moreover, Repli-seq and OK-seq analyses confirm the activating role of ATR and permit development of ATRAP-seq, a new procedure allowing mapping of early constitutive origins.

Dual DNA Replication Modes: Varying Fork Speeds and Initiation Rates within the spatial replication program inXenopus

“…It is, therefore, tempting to speculate that in the absence of Plk1, the recycling of Treslin/MTBP and TopBP1 towards neighboring origins is slowed down, resulting in a decrease in the initiation rate. In further support of this hypothesis, a recent study showed that for dormant origin firing, the linear correlation between IODs and fork speed at different concentrations of aphidicolin is also dependent on TopBP1 but not on Chk1 [67]. Another possibility is that Plk1 directly interacts with replication fork proteins to reduce fork speed.…”