Crystal Structure of the Processivity Clamp Loader Gamma Complex of E. coli DNA Polymerase III

David Jeruzalmi, Mike O'Donnell, and John Kuriyan. Cell, Vol 106, 429-441, August 2001

Summary

The gamma complex, an AAA+ ATPase, is the bacterial homolog of eukaryotic Replication Factor C (RFC) that loads the sliding clamp (beta, homologous to PCNA) onto DNA. The 2.7/3.0 Å crystal structure of gamma complex reveals a pentameric arrangement of subunits, with stoichiometry d':g3:d. The C-terminal domains of the subunits form a circular collar that supports an asymmetric arrangement of the N-terminal ATP binding domains of the gamma motor and the structurally related domains of the delta-prime stator and the delta wrench. The structure suggests a mechanism by which the gamma complex switches between a closed state, in which the beta-interacting element of delta is hidden by delta-prime, and an open form similar to the crystal structure, in which delta is free to bind to beta.

The schematic drawing below shows the gamma complex at a bacterial replication fork, attached to the two polymerase subunits of the DNA polymerase III holoenzyme. The gamma complex is shown in the act of loading a new sliding clamp (yellow) onto a newly primed piece of DNA