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A Cdt1–geminin complex licenses chromatin for DNA replication and prevents rereplication during S phase in Xenopus
Author(s) -
Lutzmann Malik,
Maiorano Domenico,
Méchali Marcel
Publication year - 2006
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/sj.emboj.7601436
Subject(s) - dna replication factor cdt1 , biology , chromatin , pre replication complex , origin recognition complex , microbiology and biotechnology , origin of replication , control of chromosome duplication , dna replication , eukaryotic dna replication , genetics , dna
Initiation of DNA synthesis involves the loading of the MCM2–7 helicase onto chromatin by Cdt1 (origin licensing). Geminin is thought to prevent relicensing by binding and inhibiting Cdt1. Here we show, using Xenopus egg extracts, that geminin binding to Cdt1 is not sufficient to block its activity and that a Cdt1–geminin complex licenses chromatin, but prevents rereplication, working as a molecular switch at replication origins. We demonstrate that geminin is recruited to chromatin already during licensing, while bulk geminin is recruited at the onset of S phase. A recombinant Cdt1–geminin complex binds chromatin, interacts with the MCM2–7 complex and licenses chromatin once per cell cycle. Accordingly, while recombinant Cdt1 induces rereplication in G1 or G2 and activates an ATM/ATR‐dependent checkpoint, the Cdt1–geminin complex does not. We further demonstrate that the stoichiometry of the Cdt1–geminin complex regulates its activity. Our results suggest a model in which the MCM2–7 helicase is loaded onto chromatin by a Cdt1–geminin complex, which is inactivated upon origin firing by binding additional geminin. This origin inactivation reaction does not occur if only free Cdt1 is present on chromatin.