DnaBDnaC

DnaB and DnaC are bacterial proteins that function together in the initiation of chromosomal DNA replication. In Escherichia coli and many other bacteria, DnaB is the replicative DNA helicase and DnaC acts as a loader that assists in placing DnaB onto the origin of replication, oriC. DnaB is a hexameric ATPase that unwinds duplex DNA to provide single-stranded templates for DNA synthesis.

DnaB helicase operates at the replication fork in a 5' to 3' direction, enabling progression of the replication machinery. Its activity is tightly coordinated with other replication factors, notably the primase (DnaG) and the DNA polymerases, which extend primers laid down on the unwound DNA. The helicase’s proper loading and activity are essential for fork establishment and progression.

DnaC serves as the helicase loader. It binds DnaB and forms a complex that is capable of delivering the helicase to the origin. DnaC also helps maintain DnaB in an appropriate, inactive state until loading is completed. Upon successful loading at oriC, ATP hydrolysis triggers the dissociation of DnaC, releasing the active DnaB helicase to unwind DNA as replication begins and primase is recruited to synthesize primers.

Across bacteria, the DnaB-DnaC system is broadly conserved, though the loader proteins can vary in name and sequence among different taxa. The interaction between DnaB, DnaC, and origin recognition by DnaA ensures the timely and controlled initiation of DNA replication. Disruption of either protein blocks replication and is typically lethal, highlighting their essential role in bacterial cell division.