The CAF-1 or chromatin assembly factor-1 consists of three subunits, and this is the first, or A [1]. The A domain is uniquely required for the progression of S phase in mouse cells [2], independent of its ability to promote histone deposition [1] but dependent on its ability to interact with HP1 - heterochromatin protein 1-rich heterochromatin domains next to centromeres that are crucial for chromosome segregation during mitosis. This HP1-CAF-1 interaction module functions as a built-in replication control for heterochromatin, which, like a control barrier, has an impact on S-phase progression in addition to DNA-based checkpoints [2].

1: Essential role of chromatin assembly factor-1-mediated rapid nucleosome assembly for DNA replication and cell division in vertebrate cells. Takami Y, Ono T, Fukagawa T, Shibahara K, Nakayama T; Mol Biol Cell. 2007;18:129-141. PMID:17065558

2: The HP1-p150/CAF-1 interaction is required for pericentric heterochromatin replication and S-phase progression in mouse cells. Quivy JP, Gerard A, Cook AJ, Roche D, Almouzni G; Nat Struct Mol Biol. 2008;15:972-979. PMID:19172751