Chromatin assembly: biochemical identities and genetic redundancy

Investigations on chromatin assembly in vitro implicate chromatin assembly factor 1 (CAF1) as a chaperone for histones H3/H4 and nucleosome assembly p rotein 1 (NAP1) as a chaperone for histones H2A/H2B, Deletion analysis of C AF1 in vivo suggests multiple redundant pathways for deposition of the hist ones. Histone deposition requires acetylation of the amino-terminal tails a nd analysis of mutants suggests a specific but redundant role for acetylati on of the tails in assembly. Furthermore, studies on the HAT1 acetyltransfe rase raise the possibility that acetylation of histones occurs following th eir transport into the nucleus but prior to their deposition onto DNA. Iden tification of the factors involved in the redundant pathways of assembly is awaited.