Hydroxyurea-induced accumulation of short fragments during polyoma DNA replication. II. Behavior during incubation of isolated nuclei.

The synthesis of polyoma DNA was studied in isolated nuclei from hydroxyurea-inhibited 3T6 cells infected with polyoma virus. During incubation of nuclei under conditions suitable for polyoma DNA synthesis in vitro, the short DNA fragments with a sedimentation coefficient of 4S formed in vivo (hydroxyurea fragments) became associated with preformed, replicating DNA strands. Centrifugation in dye-buoyant density gradients showed that the fragments formed part of the structure of the replicative intermediate of polyoma DNA. The proportion of "young" replicative intermediates was larger after hydroxyurea inhibition than in uninhibited controls. Hydroxyurea fragments appear to be closely related to the 4S fragments formed as normal intermediates during discontinuous synthesis of polyoma DNA.