The ring-shaped hexameric DnaB helicase unwinds duplex DNA at the replication
fork of eubacteria. We have solved the crystal structure of the full-length
Thermus aquaticus DnaB monomer, or possibly dimer, at 2.9 A resolution. DnaB is
a highly flexible two domain protein. The C-terminal domain exhibits a RecA-like
core fold and contains all the conserved sequence motifs that are characteristic
of the DnaB helicase family. The N-terminal domain contains an additional
helical hairpin that makes it larger than previously appreciated. Several DnaB
mutations that modulate its interaction with primase are found in this hairpin.
The similarity in the fold of the DnaB N-terminal domain with that of the
C-terminal helicase-binding domain (HBD) of the DnaG primase also includes this
hairpin. Comparison of hexameric homology models of DnaB with the structure of
the papillomavirus E1 helicase suggests the two helicases may function through
different mechanisms despite their sharing a common ancestor.
