DDK has a primary role in processing stalled replication forks to initiate downstream checkpoint signaling

Abstract

CDC7-DBF4 kinase (DDK) is required to initiate DNA replication in eukaryotes by activating the replicative MCM helicase. DDK has also been reported to have diverse and sometimes conflicting roles in the replication checkpoint response in various organisms but the underlying mechanisms are far from settled. Here we show that human DDK promotes limited resection of newly synthesized DNA at stalled replication forks or sites of DNA damage to initiate replication checkpoint signaling. DDK is also required for efficient fork restart and G2/M cell cycle arrest. DDK exhibits genetic interactions with the ssDNA exonuclease EXO1, and we show that EXO1 is also required for nascent strand degradation following exposure to HU, raising the possibility that DDK regulates EXO1 directly. Thus, DDK has a primary and previously undescribed role in the replication checkpoint to promote ssDNA accumulation at stalled forks, which is required to initiate a robust checkpoint response and cell cycle arrest to maintain genome integrity.