Identification of a region of Escherichia coli DnaB required for functional interaction with DnaG at the replication fork

The fundamental activities of the replicative primosomes of Escherichia coi l are provided by DnaB, the replication fork DNA helicase, and DnaG, the Ok azaki fragment primase. As we have demonstrated previously, DnaG is recruit ed to the replication fork via a transient protein-protein interaction with DnaB. Here, using site-directed amino acid mutagenesis, we have defined th e region on DnaB required for this protein-protein interaction. Mutations i n this region of DnaB affect the DnaB-DnaG; interaction during both general priming-directed and phi X174 complementary strand DNA synthesis, as well as at replication forks reconstituted in rolling circle DNA replication rea ctions. The behavior of the purified mutant DnaB proteins in the Various re plication systems suggests that access to the DnaG binding pocket on DnaB m ay be restricted at the replication fork.