Postreplicative Chromatin Assembly by Drosophila and Human Chromatin Assembly Factor 1

To study the relationship between DNA replication and chromatin assembly, we have purified a factor termed Drosophila chromatin assembly factor 1 (dCAF-1) to approximately 50% homogeneity from a nuclear extract derived from embryos. dCAF-1 appears to consist of four polypeptides with molecular masses of 180, 105, 75, and 55 kDa. dCAF-1 preferentially mediates chromatin assembly of newly replicated DNA relative to unreplicated DNA during T-antigen-dependent simian virus 40 DNA replication in vitro, as seen with human CAF-1. Analysis of the mechanism of DNA replication-coupled chromatin assembly revealed that both dCAF-1 and human CAF-1 mediate chromatin assembly preferentially with previously yet newly replicated DNA relative to unreplicated DNA. Moreover, the preferential assembly of the postreplicative DNA was observed at 30 min after inhibition of DNA replication by aphidicolin, but this effect slowly diminished until it was no longer apparent at 120 min after inhibition of replication. These findings suggest that the coupling between DNA replication and chromatin assembly may not necessarily involve a direct interaction between the replication and assembly factors at a replication fork.