Replication of bacteriophage φX174 replicative form DNA in vivo

The replication of the circular double-stranded bacteriophage φX174 replicative form DNA was studied by structural analysis of pulse-labelled replicative intermediates. Evidence is presented that φX replicative form replicates according to a rolling circle model proposed by Dressler & Wolfson (1970). Replication involves continuous elongation of the viral strand component of replicative form resulting in the displacement of a single-stranded tail of increasing length. Replicative intermediates sedimenting at 27 to 28s are found to contain linear viral strands of approximately double φX unit length. The synthesis of the new complementary strand on the single-stranded viral tail appears to be initiated with considerable delay and converts the tail to double-stranded DNA. At some time, but before the new complementary strand is completed, the replicative intermediates split to give consequently one replicative form molecule containing the old complementary and the new viral strand and a linear partially double-stranded tail which matures to replicative form by circularization and completion of the new complementary strand