Newly-initiated DNA isolated from Physarum in early S phase consists of nascent-nascent duplexes.

We have studied the nature of newly initiated DNA released during DNA isolation at the beginning of S phase of Physarum polycephalum. The released DNA was separated from the bulk DNA by sedimentation through sucrose gradients. Gentle shearing strongly enhanced the release of newly initiated DNA. The additionally released material had a larger average molecular weight. Buoyant density analysis after labelling with bromodeoxyuridine (BrdU) revealed that the released DNA consisted of nascent-nascent duplexes for more than 90%. This indicates that the release of newly initiated DNA occurs by branch migration. We conclude that shearing enhances branch migration by destabilization of the double helix.