In metazoans, accurate replication of chromosomes is ensured by the coupling of DNA synthesis to the synthesis of histone proteins. Expression of replication-dependent histone genes is restricted to S-phase by a combination of cell cycle-regulated transcriptional and post-transcriptional control mechanisms and is linked to DNA replication by a poorly understood mechanism involving checkpoint kinases [Su, Gao, Schneider, Helt, Weiss, O'Reilly, Bohmann and Zhao (2004) EMBO J. 23, 1133-1143; Kaygun and Marzluff (2005) Nat. Struct. Mol. Biol. 12, 794-800]. Here we propose a model for the molecular mechanisms that link these two important processes within S-phase, and propose roles for multiple checkpoints in this mechanism.