cd09867

PIN domain of Flap Endonuclease-1, a structure-specific, divalent-metal-ion dependent, 5' nuclease and homologs; Flap endonuclease-1 (FEN1) is involved in multiple DNA metabolic pathways, including DNA replication processes (5' flap DNA endonuclease activity and double stranded DNA 5'-exonuclease activity) and DNA repair processes (long-patch base excision repair) in eukaryotes and archaea. Interaction between FEN1 and PCNA (Proliferating cell nuclear antigen) is an essential prerequisite to FEN1's DNA replication functionality and stimulates FEN1 nuclease activity by 10-50 fold. FEN1 belongs to the FEN1-EXO1-like family of structure-specific, 5' nucleases. These nucleases contain a PIN (PilT N terminus) domain with a helical arch/clamp region (I domain) of variable length (approximately 45 residues in FEN1 PIN domains) and a H3TH (helix-3-turn-helix) domain, an atypical helix-hairpin-helix-2-like region. Both the H3TH domain (not included here) and the helical arch/clamp region are involved in DNA binding. Nucleases within this group also have a carboxylate-rich active site that is involved in binding essential divalent metal ion cofactors (Mg2+/Mn2+). FEN1 has a C-terminal extension containing residues forming the consensus PIP-box - Qxx(M/L/I)xxF(Y/F) which serves to anchor FEN1 to PCNA.