POSTREPLICATIVE CHROMATIN ASSEMBLY BY DROSOPHILA AND HUMAN CHROMATIN ASSEMBLY FACTOR-1

To study the relationship between DNA replication and chromatin assemb ly, we have purified a factor termed Drosophila chromatin assembly fac tor I (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 preferential ly mediates chromatin assembly of newly replicated DNA relative to unr eplicated DNA during T-antigen-dependent simian virus 40 DNA replicati on in vitro, as seen with human CAF-1. Analysis of the mechanism of DN A replication-coupled chromatin assembly revealed that both dCAF-I ari d human CAF-1 mediate chromatin assembly preferentially with previousl y yet newly replicated DNA relative to unreplicated DNA. Moreover, the preferential assembly of the postreplicative DNA was observed at 30 m in after inhibition of DNA replication by aphidicolin, but this effect slowly diminished until it was no longer apparent at 120 min after in hibition of replication. These findings suggest that the coupling betw een DNA replication and chromatin assembly may not necessarily involve a direct interaction between the replication and assembly factors at a replication fork.