Enzymology of the pre-priming steps in lambda dv DNA replication in vitro

We have examined some of the early pre-priming steps of bacteriophage lambda dv DNA replication in vitro. Previous experiments have shown that bacteriophage lambda replication requires host RNA polymerase-dependent RNA synthesis near or at the origin of replication (ori lambda) to initiate DNA synthesis. Using a crude Fraction II enzymatic system we have shown that during RNA polymerase action, at least the bacteriophage lambda O and lambda P replication proteins as well as the host dnaB protein must be present to initiate ori lambda-specific DNA replication. The presence of three other host initiation proteins, dnaG primase, dnaJ, and dnaK, is not required during RNA polymerase action. Because of the apparent absence of a requirement for the dnaJ and dnaK pre-priming proteins during the transcriptional activation step, we propose that the early events of lambda dv DNA replication, prior to action by the dnaG primase, can be divided into two recognizable steps: an early step which requires at least RNA polymerase, lambda O, lambda P, and dnaB, and a subsequent step which requires the action of at least the dnaJ and dnaK proteins.