| Description | Sliding DNA clamps are ring-shaped proteins that allow DNA polymerase to achieve high processivity during chromosome replication by tethering the polymerase catalytic subunit to DNA [ , ]. The sliding clamp is required by many different enzymes for DNA replication and repair [] and is found both in prokaryotes and eukaryotes. In eukaryotes, it is generally known as proliferating cell nuclear antigen (PCNA) and is a heterotrimer while the prokaryotic one is a homodimer. All of the structures share a 12-fold symmetry around the ring consisting of a simple structural repeat, though there is structural divergence in some of the repeats. Bacterial β-clamps contain six repeats per subunit with two subunits per ring while the eukaryotic and bacteriophage clamps contain four repeats per subunit with three subunits per ring. Pairs of these repeats form a domain, which has been termed the 'processivity fold'; thus the ring of the sliding clamp contains six domains and therefore is often described as having 6-fold symmetry. A structural representative of a fourth family of processivity fold proteins, namely the herpes simplex virus UL42 protein, is also available. UL42 does not form a ring-shaped clamp, however, but rather functions as a monomer and interacts with DNA quite differently than do sliding clamps. It has been suggested that UL42 resembles a primitive ancestor of sliding clamps []. | Name | DNA clamp superfamily |
| Short Name | DNA_clamp_sf | Type | Homologous_superfamily |
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