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Protein family review

The ring-type polymerase sliding clamp family

Irina Bruck* and Mike O'Donnell

Author Affiliations

Howard Hughes Medical Institute and Rockefeller University, 1230 York Avenue, New York, NY 10021, USA

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Genome Biology 2001, 2:reviews3001-reviews3001.3  doi:10.1186/gb-2001-2-1-reviews3001

Published: 9 January 2001

Abstract

Ring-type polymerases consist of a DNA polymerase, a ring-shaped sliding clamp protein and a clamp-loading complex. Sliding clamp proteins are found in all organisms and are called proliferating cell nuclear antigen (PCNA) in eukaryotes and the β clamp in prokaryotes. Both PCNA and β form a ring around DNA, which is made up of two subunits of three domains each in β but three subunits of two domains each in PCNA. Despite this difference and a lack of detectable sequence homology, the structures of the two rings are very similar. The sliding clamp slides along DNA and tethers the polymerase to the DNA, enabling rapid and processive DNA replication.