The Escherichia coli chaperones involved in DNA replication

Mutations in the Escherichia coli heat shock genes, dnaK, dnaJ or grpE, alter host DNA and RNA synthesis, degradation of other proteins, cell division and expression of other heat shock genes. They also block the initiation of DNA replication of bacteriophages lambda and P1, and the mini-F plasmid. An in vitro lambda DNA replication system, composed entirely of purified components, enabled us to describe the molecular mechanism of the dnaK, dnaJ and grpE gene products. DnaK, the bacterial hsp 70 homologue, releases lambda P protein from the preprimosomal complex in an ATP- and DnaJ-dependent reaction (GrpE-independent initiation of lambda DNA replication). In this paper, I show that, when GrpE is present, lambda P protein is not released from the preprimosomal complex, rather it is translocated within the complex in such a way that it does not inhibit DnaB helicase activity. Translocation of lambda P triggers the initiation event allowing DnaB helicase to unwind DNA near the ori lambda sequence, leading to efficient lambda DNA replication. Chaperone activity of the DnaK-DnaJ-GrpE system is first manifested in the selective binding of these heat shock proteins to the preprimosomal complex, followed by its ATP-dependent rearrangement. I show that DnaJ not only tags the preprimosomal complex for recognition by DnaK, but also stabilizes the multi-protein structure. GrpE also participates in the binding of DnaK to the preprimosomal complex by increasing DnaK's affinity to those lambda P proteins which are already with DnaJ.(ABSTRACT TRUNCATED AT 250 WORDS)