Convergent evolution in two bacterial replicative helicase loaders

Trends Biochem Sci. 2022 Jul;47(7):620-630. doi: 10.1016/j.tibs.2022.02.005. Epub 2022 Mar 26.


Dedicated loader proteins play essential roles in bacterial DNA replication by opening ring-shaped DnaB-family helicases and chaperoning single-stranded (ss)DNA into a central motor chamber as a prelude to DNA unwinding. Although unrelated in sequence, the Escherichia coli DnaC and bacteriophage λ P loaders feature a similar overall architecture: a globular domain linked to an extended lasso/grappling hook element, located at their N and C termini, respectively. Both loaders remodel a closed DnaB ring into nearly identical right-handed open conformations. The sole element shared by the loaders is a single alpha helix, which binds to the same site on the helicase. Physical features of the loaders establish that DnaC and λ P evolved independently to converge, through molecular mimicry, on a common helicase-opening mechanism.

Keywords: DNA replication; DnaB; DnaC, λ P; convergent evolution; helicase loading.

Publication types

  • Review
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / metabolism
  • DNA Helicases / metabolism
  • DNA Replication
  • DNA, Single-Stranded
  • DnaB Helicases / chemistry
  • DnaB Helicases / genetics
  • DnaB Helicases / metabolism
  • Escherichia coli / metabolism
  • Escherichia coli Proteins* / chemistry


  • Bacterial Proteins
  • DNA, Single-Stranded
  • Escherichia coli Proteins
  • DNA Helicases
  • DnaB Helicases