InterPro domain: IPR017961

This entry represents the little finger domain found in Y-family (lesion bypass) DNA polymerases. Y-family polymerases were originally known as UmuC/DinB/Rev1/Rad30 after each branch of the family. These enzymes are characterised by their low-fidelity synthesis on undamaged DNA templates and by their ability to traverse replication-blocking lesions. By contrast, high-fidelity polymerases (such as DNA polymerase III) are sensitive to distortions in the DNA template. As a result, Y-family polymerases can extend primer strands across DNA strand lesions that would otherwise stall replicative polymerases. To minimize mutations through their low fidelity synthesis, these enzymes are regulated, and are thought to interact with processivity factors, beta-clamp or proliferating cell nuclear antigen (PCNA), which are also essential for the function of replicative DNA polymerases [ 1 ]. Organisms can contain more than one Y-family polymerase, each with a unique DNA damage bypass and fidelity profile. For example, humans posses four Y-family polymerases: DNA polymerases kappa, iota, eta and Rev1. Y-family polymerases show no homology to DNA polymerases from the A-, B-, C-, D- or X-families [ 2 ].

The Y-family of DNA polymerases includes the following enzymes:

• Prokaryotic DNA polymerase IV (DinB) [ 3 ].
• Archaeal DinB homologue DNA polymerase IV [ 3 ].
• Eukaryotic DinB homologue DNA polymerase kappa [ 3 ].
• Prokarytoic DNA repair proteins UmuC and UmuD [ 4 ].
• Eukaryotic Rad30 homologues DNA polymerase eta and iota [ 5 , 6 ].
• Eukaryotic DNA repair protein Rev1 [ 7 ].

Human DNA polymerase kappa is a right-handed shaped molecule with palm, fingers, thumb, little finger and wrist subdomains [ 8 ].

1. Structural basis for recruitment of translesion DNA polymerase Pol IV/DinB to the beta-clamp. EMBO J. 22, 5883-92
2. Crystal structure of a Y-family DNA polymerase in action: a mechanism for error-prone and lesion-bypass replication. Cell 107, 91-102
3. Crystal structure of the catalytic core of human DNA polymerase kappa. Structure 12, 1395-404
4. Y-family DNA polymerases in Escherichia coli. Trends Microbiol. 15, 70-7
5. Structure of the catalytic core of S. cerevisiae DNA polymerase eta: implications for translesion DNA synthesis. Mol. Cell 8, 417-26
6. Hoogsteen base pair formation promotes synthesis opposite the 1,N6-ethenodeoxyadenosine lesion by human DNA polymerase iota. Nat. Struct. Mol. Biol. 13, 619-25
7. Novel conserved motifs in Rev1 C-terminus are required for mutagenic DNA damage tolerance. DNA Repair (Amst.) 7, 1455-70