Nucleosome segregation at a defined mammalian chromosomal site.

Abstract

When animal cells replicate chromatin under conditions precluding new histone biosynthesis, half of the daughter DNA are devoid of nucleosomes and are sensitive to staphylococcal nuclease. DNA sequences resistant to nuclease are associated with preexisting nucleosomes, which redistribute to progeny DNA duplexes during replication. Newly replicated DNA sequences in a SV40-transformed Chinese hamster cell clone were labeled with 5-bromodeoxyuridine (BrdUrd) in the presence and absence of a protein biosynthesis inhibitor, emetine. Single-stranded BrdUrd- and dT-DNA sequences protected from nuclease digestion by nucleosomes and determined from which strands of the integrated viral DNA parental template (dT) and newly replicated progeny (BrdUrd) sequences were derived. The cell clone studied contained all of its integrated SV40 DNA at a single chromosomal site, preexisting nucleosomes segregated to only 1 of the 2 daughter duplexes containing the integrated viral sequences. In the presence of emetine, the integrated viral origin of replication, ORIsv, appeared not to function as a chromosomal replication origin, perhaps reflecting the drug''s effect on synthesis of SV40 large tumor antigen.