Size distribution of DNA replicative intermediates in bacteriophage P4 and in Escherichia coli.

We have tested the hypothesis that Okazaki fragment replicative intermediates have defined termini using as a model system the in vivo DNA replication of the tiny bacteriophage P4. The kinetics of formation of intermediates in P4 DNA replication have been investigated. P4 DNA replication in DNA polymerase I-deficient mutants generates Okazaki fragments with a size distribution similar to that in uninfected cells. When P4-derived Okazaki fragments are resolved by agarose gel electrophoresis, no discrete size classes appear. This finding is incompatible with sequence-specific models of Okazaki fragment formation but supports the view that these replication intermediates are initiated and terminated at random locations on the P4 chromosome.