Studies on the structure of replicative intermediates in bacteriophage M13 single stranded DNA synthesis.

Pulse-labeled replicative intermediates in M 13 single stranded DNA synthesis can be separated by dye-buoyant density centrifugation into two major fractions: Supercoiled molecules (RI I) containing viral strands of more than one genome length, and "relaxed" molecules (RI II) with labeled DNA chains shorter than unit length. It is postulated that RI II molecules might be formed in vivo by site-specific nicking of RF I molecules.