Abstract
Through the passage of replication fork, parental nucleosomes are transiently disassembled and transferred to the newly synthesized DNA (parental nucleosome segregation), and the nascent histones H3-H4 tetramers are also deposited onto newly replicated DNA behind the replication fork (de novo nucleosome assembly), followed by loading of H2A-H2B dimers to complete nucleosome formation.CAF-1, composed of p150, p60, and p48 subunits, was purified from human cell nuclear extract as an activity to promote nucleosome assembly of replicating DNA in SV40 replication system. CAF-1 is recruited in replication foci with nascent histones H3-H4 in human cells, via interaction with DNA polymerase sliding clump, PCNA (Shibahara and Stillman, 1999, Cell). Therefore, CAF-1 is a prime candidate for the factor involved in, at least, the de novo nucleosome assembly. CAF-1 also mediates nucleosome assembly during NER following UV irradiation. Null mutations of CAF-1 homologue in Arabidopsis displayed unstable propagation of gene expression through plant growth and mild sensitivity to various DNA damaging agents including MMS and IR (Kaya et al., Cell, 2004; submitted). Recently, we analyzed conditional knockout chicken DT40 cells in which CAF-1 can be depleted by addition of tetracycline. CAF-1 depletion led to delayed S-phase progression with retarded DNA synthesis and defects in a rapid nucleosome formation of newly replicated DNA. Furthermore, we obtained some evidence suggesting that CAF-1 is involved in the activation of replication checkpoint via Chk1 (Takami et al., submitted).
