The key regulatory checkpoint for DNA replication completion before mitosis is:
Before mitosis, cells must verify complete and accurate genome duplication to avoid mitotic breakage of under-replicated chromosomes. G2/M checkpoint operates as surveillance system mediated by ATR-Chk1 and ATM-Chk2 kinases activated by RPA-coated single-stranded DNA at stalled forks and double-strand breaks respectively. Chief effectors are Cdc25 phosphatase family isoforms B and C that normally remove inhibitory Thr14 and Tyr15 phosphorylations placed on CDK1 by Wee1 and Myt1 nuclear kinases, triggering abrupt CDK1 activation. Checkpoint kinases phosphorylate Cdc25B/C at Ser216 and Ser323 ge
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 20: G2/M Checkpoint and Replication Completion.