Plasmid and host functions required for lambda plasmid replication carried out by the inherited replication complex

Abstract

We have shown previously that in amino acid-starved, relaxed (rel-) mutants of Escherichia coli replication of the lambda plasmid occurs via the lambda O-containing replication complex (RC) that was assembled prior to the onset of amino acid starvation and is inherited by one of the two daughter plasmid circles in each replication cycle. This replication is regulated neither by binding of the lambda O initiator to ori lambda, nor by the lambda Cro-mediated repression. Here we show that it is dependent on both RNA polymerase and DnaA functions, which is consistent with our recent finding that transcriptional activation of ori lambda is under the control of DnaA. In the system studied, DnaA-regulated transcriptional activation of ori lambda seems to be the only rate-limiting process. The lambda plasmid replication mediated by the inherited RC appeared to be independent of the functions of lambda P and DnaJ required in RC assembly In vitro experiments performed by others suggest that DnaJ first binds to the ori lambda-bound lambda O-lambda P-DnaB pre-primosome and subsequently lambda P complexed with DnaJ is preferentially recognized by DnaK-GrpE; chaperone-mediated rearrangement of this structure relieves DnaB helicase of lambda P inhibition. Recently we proposed that this process is directly coupled to the insertion of the pre-primosome between DNA strands transiently separated by transcription. This last-mentioned process may be required in lambda plasmid replication mediated by the inherited RC, which appeared in turn to be dependent on DnaK and GrpE functions.