The RCAF complex mediates chromatin assembly during DNA replication and repair

Chromatin assembly is a fundamental biological process that is essential fo r the replication and maintenance of the eukaryotic genome(1-4). In dividin g cells, newly synthesized DNA is rapidly assembled into chromatin by the d eposition of a tetramer of the histone proteins H3 and H4, followed by the deposition of two dimers of histones H2A and H2B to complete the nucleosome -the fundamental repeating unit of chromatin(5). Here we describe the ident ification, purification, cloning, and characterization of replication-coupl ing assembly factor (RCAF), a novel protein complex that facilitates the as sembly of nucleosomes onto newly replicated DNA in vitro. RCAF comprises th e Drosophila homologue of anti-silencing function 1 protein ASF1(6) and his tones H3 and H4. The specific acetylation pattern of H3 and H4 in RCAF is i dentical to that of newly synthesized histones. Genetic analyses in Sacchar omyces cerevisiae demonstrate that ASF1 is essential for normal fell cycle progression, and suggest that RCAF mediates chromatin assembly after DNA re plication and the repair of double-strand DNA damage in vivo.