The rolling circle for phi X DNA replication. 3. Synthesis of supercoiled duplex rings

During varphiX duplex ring synthesis, the first supercoils to acquire radioactivity after the addition of tritiated thymidine are labeled only in their negative strands. In longer pulses, this asymmetry of labeling progressively disappears. This finding supports the rolling circle model for DNA replication due to the structural asymmetry of its replicating intermediate, but is not predicted by the Cairns or Yoshikawa models.