VCP/p97 extracts DNA polymerase α/Primase from chromatin to limit the activation of the replication stress response

The replication stress response is an essential pathway that deals with the lesions that halt the progression of DNA replication forks even during an unperturbed S phase. Basal activation of the ATR and CHK1 kinases prevents the premature firing of origins of replication during S phase, avoiding the activation of an excessive number of replication forks and the appearance of genomic instability. However, the mechanisms that regulate ATR activation in the unperturbed S phase have not been fully determined. Here we present evidence showing that the AAA ATPase VCP/p97 regulates the presence of the DNA polymerase α/Primase complex (POLA/PRIM) on chromatin after origin firing, thus limiting the generation of primed DNA structures that mediate the activation of ATR by TOPBP1. As a consequence, inhibiting VCP/p97 activates ATR and CHK1 leading to cell cycle arrest in G2/M. We propose that the loading of POLA/PRIM after origin firing drives the basal activation of ATR during an unperturbed S phase and VCP/p97 regulates this activation through the extraction of POLA/PRIM from chromatin.