DnaB

DnaB is a bacterial DNA helicase that plays a central role in DNA replication. In many bacteria, notably Escherichia coli, DnaB is a hexameric ring-shaped motor that encircles single-stranded DNA and uses energy from ATP hydrolysis to translocate along the lagging-strand template in the 5' to 3' direction, unwinding the duplex ahead of the replication fork. This unwinding provides the template for leading- and lagging-strand synthesis by the DNA polymerase III holoenzyme.

During initiation, the helicase is loaded at the origin of replication (oriC) by the helicase loader DnaC. The DnaB-DnaC complex facilitates loading of the DnaB ring onto the DNA; after successful loading, DnaC dissociates, allowing DnaB to interact with the primase DnaG to form the primosome. The primase synthesizes RNA primers on the lagging strand, enabling the lagging-strand synthesis that is coordinated with continuous leading-strand replication.

Functionally, DnaB is a key component of the bacterial replisome, coordinating with the DnaG primase, the clamp-loader complex containing tau subunits, and the DNA polymerase III holoenzyme. Through these interactions, DnaB coordinates strand separation with primer synthesis and polymerase activity, ensuring efficient and processive replication of the genome.

Structureally, DnaB consists of distinct N-terminal and C-terminal domains; the C-terminal region contains the ATPase motor responsible for translocation, while the N-terminal region mediates interactions with DnaG. Regulation of DnaB activity arises from nucleotide state, protein-protein interactions, and loading status at the replication fork.

Significance: DnaB is essential for bacterial viability and serves as a model for helicase mechanisms and replisome dynamics. It is a potential target for antibacterial strategies aimed at disrupting DNA replication.