Role of amino-terminal histone domains in chromatin replication.

Simian virus 40 minichromosomes were treated with trypsin to specifically remove the amino-terminal histone domains (tails). Trypsin treatment does not affect the spacing and the number of nucleosomes on minichromosomes but indices a more extended conformation, as shown by the reduced sedimentation coefficient of trypsinized minichromosomes compared with the untreated controls. Trypsinized minichromosomes replicate more efficiently than control minichromosomes in in vitro replication assays. The increased template efficiency appears to be due to higher rates of replicative fork movement. In vitro replication in the presence of protein-free competitor DNA shows that replicating trypsinized minichromosomes do not lose nucleosomes and replicating competitor DNA does not gain nucleosomes. This finding suggests that tailless nucleosomes are transferred from the unreplicated prefork stem to replicated DNA branches and excludes a participation of the basic histone domains in nucleosome transfer.