Re-replication of SV40 minichromosomes is inhibited at the stage of chain elongation.

The template activities of protein-free SV40 DNA and SV40 minichromosomes for DNA re-replication are compared in in vitro replication assays. Density substitution experiments and two-dimensional gel electrophoresis show that protein-free DNA can replicate for at least two cycles whereas salt-treated minichromosomes replicate only once. Re-replication of minichromosomes is blocked at the stage of replicative chain elongation suggesting that replicatively assembled chromatin has structural features that prevent a second round of replication.