FIG. 9.

Model for bidirectional propagation of nucleosomal arrays facilitated by the interaction of CAF-1 with PCNA sliding clamps during DNA damage processing. The initiation of this nucleosome assembly process is dependent on the presence of single-strand breaks and gaps produced either by direct DNA damage or during excision repair. The recruitment to repair sites of PCNA and the histone chaperone CAF-1 (together with H3/H4) requires ATP. The amino terminus of CAF-1 p150 is engaged in a stable interaction with specific sites on the outer front side of PCNA. The ability of the PCNA toroidal ring to slide along the DNA helix provides a possible mechanism for nucleosomal arrays to propagate bidirectionally from sites of repair (indicated by the arrows). The hatched nucleosome represents an undefined structure at the repair site.