Heterochromatin dynamics in mouse cells: Interaction between chromatin assembly factor 1 and HP1 proteins

Mechanisms contributing to the maintenance of heterochromatin in proliferat ing cells are poorly understood. We demonstrate that chromatin assembly fac tor 1 (CAF-1) binds to mouse HP1 proteins via an N-terminal domain of its p 150 subunit, a domain dispensable for nucleosome assembly during DNA replic ation. Mutations in p150 prevent association with HP1 in heterochromatin in cells that are not in S phase and the formation of CAF-1-HP1 complexes in nascent chromatin during DNA replication in vitro. We suggest that CAF-1 p1 50 has a heterochromatin-specific function distinct from its nucleosome ass embly function during S phase. Just before mitosis, CAF-1 p150 and some HP1 progressively dissociate from heterochromatin concomitant with histone H3 phosphorylation. The HP1 proteins reassociate with chromatin at the end of mitosis, as histone H3 is dephosphorylated.