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Abstract
Simian virus 40 (SV40) minichromosomes were used as the substrate for in vitro replication. Protein-free SV40 DNA or plasmids, carrying the SV40 origin of replication, served as controls. Replicated minichromo-somal DNA possessed constrained negative superhelicity indicative of the presence of nucleosomes. The topological state of replicated minichromosomal DNA was precisely determined by two-dimensional gel electrophoresis. We show that most or all nucleosomes, present on the replicated minichromosomal DNA, were derived from the parental minichromosome substrate. The mode and the rate of nucleosome transfer from parental to minichromosomal daughter DNA were not influenced by high concentrations of competing replicating and nonreplicating protein-free DNA, indicating that nucleosomes remain associated with DNA during the replication process. The data also show that parental nucleosomes were segregated to the replicated daughter DNA strands in a dispersive manner.