Composition of the lambda plasmid heritable replication complex

Previous studies indicated during replication of plasmids derived from bacteriophage lambda (the so-called lambda plasmids), that, once assembled, replication complex can be inherited by one of the two daughter plasmid copies after each replication round, and may function in subsequent replication rounds. It seems that similar processes occur during replication of other DNA molecules, including chromosomes of the yeast Saccharomyces cerevisiae. However, apart from some suggestions based on genetic experiments, composition of the lambda heritable replication complex remains unknown. In amino acid-starved Escherichia coli relA mutants, replication of lambda plasmid DNA is carried out exclusively by the heritable replication complex as assembly of new complexes is impaired due to inhibition of protein synthesis. Here, using a procedure based on in vivo cross-linking, cell lysis, immunoprecipitation with specific sera, de-cross-linking and PCR analysis, we demonstrate that the lambda heritable replication complex consists of O, P, DnaB and, perhaps surprisingly, DnaK proteins.