This paper presented the first crystal structure of a "processivity factor" for a DNA polymerase.
DNA polymerases that replicate entire genomes during cell division are able to move along DNA very rapidly without
letting go. Mike O'Donnell (HHMI, Rockefeller University) showed that the tight association with DNA during
replication depends upon the processivity factor, a protein assembly that holds the polymerase onto DNA
due to a topological linkage. The processivity factor is also known as a "sliding DNA clamp"
(a term introduced by Huang, Hearst and Alberts).
By determining the three-dimensional structure of the processivity factor of bacterial DNA polymerase (the beta-subunit),
we established (in collaboration with Mike O'Donnell) that the processivity factor is a ring-shaped and
highly symmetrical assembly through which DNA can be threaded.
The high symmetry of the beta-subunit assembly allowed a connection to be made between the architecture of this
ring-shaped assembly seen in bacteria and the processivity factors of eukaryotic (including human) and
bacteriophage DNA polymerases.