FEN-like PIN domains of bacteriophage T3, T4 RNase H, T5-5'nuclease, and homologs; PIN (PilT N terminus) domain of bacteriophage T5-5'nuclease (5'-3' exonuclease or T5FEN), bacteriophage T4 RNase H (T4FEN), bacteriophage T3 (T3 phage exodeoxyribonuclease) and other similar 5' nucleases are included in this family. T5-5'nuclease is a 5'-3'exodeoxyribonuclease that also exhibits endonucleolytic activity on flap structures (branched duplex DNA containing a free single-stranded 5'end). T4 RNase H, which removes the RNA primers that initiate lagging strand fragments, has 5'- 3'exonuclease activity on DNA/DNA and RNA/DNA duplexes and has endonuclease activity on flap or forked DNA structures. Bacteriophage T3 is believed to function in the removal of DNA-linked RNA primers and is essential for phage DNA replication and also necessary for host DNA degradation and phage genetic recombination. These nucleases are members of the structure-specific, 5' nuclease family (FEN-like) that catalyzes hydrolysis of DNA duplex-containing nucleic acid structures during DNA replication, repair, and recombination. Canonical members of the FEN-like family possess a PIN domain with a two-helical structure insert (also known as the helical arch, helical clamp or I domain) of variable length (approximately 16 to 800 residues), and at the C-terminus of the PIN domain a H3TH (helix-3-turn-helix) domain, an atypical helix-hairpin-helix-2-like region. Both the H3TH domain (not included in this model) and the helical arch/clamp region are involved in DNA binding. The PIN domain belongs to a large nuclease superfamily. The structural properties of the PIN domain indicate its putative active center, consisting of invariant acidic amino acid residues (putative metal-binding residues), is geometrically similar in the active center of structure-specific 5' nucleases, PIN-domain ribonucleases of eukaryotic rRNA editing proteins, and bacterial toxins of toxin-antitoxin (TA) operons. In the T5-5'nuclease, structure-specific endonuclease activity requires binding of a single metal ion in the high-affinity, metal binding site 1, whereas exonuclease activity requires both, the high-affinity, metal binding site 1 and the low-affinity, metal binding site 2 to be occupied by a divalent cofactor. The T5-5'nuclease is reported to be able to bind several metal ions including, Mg2+, Mn2+, Zn2+ and Co2+, as co-factors.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1841998963   2 VVLAFTDDVNWRKVLVDETYKENRKATR----KPVGY----RDFLSKLWERDEFIHIKEDMLEGDDVMGIIGSGHEVFGF 73
Cdd:cd09860    47 KPIVLWDGRASWRKDLFPEYKANRKKTReekkAWREAfeaqRPFIEEALEYLGVPQIRAPGAEADDLAGVLVKRLAAFGD 126

                          90       100       110
                  ....*....|....*....|....*....|...
gi 1841998963  74 KkAVLVSCDKDFKTIPDVDFLWCTTGNILTQTK 106
Cdd:cd09860   127 K-VLLVSGDKDWLQLVYENVSWFSPITDKEVTL 158

FEN-like PIN domains of bacteriophage T3, T4 RNase H, T5-5'nuclease, and homologs; PIN (PilT N terminus) domain of bacteriophage T5-5'nuclease (5'-3' exonuclease or T5FEN), bacteriophage T4 RNase H (T4FEN), bacteriophage T3 (T3 phage exodeoxyribonuclease) and other similar 5' nucleases are included in this family. T5-5'nuclease is a 5'-3'exodeoxyribonuclease that also exhibits endonucleolytic activity on flap structures (branched duplex DNA containing a free single-stranded 5'end). T4 RNase H, which removes the RNA primers that initiate lagging strand fragments, has 5'- 3'exonuclease activity on DNA/DNA and RNA/DNA duplexes and has endonuclease activity on flap or forked DNA structures. Bacteriophage T3 is believed to function in the removal of DNA-linked RNA primers and is essential for phage DNA replication and also necessary for host DNA degradation and phage genetic recombination. These nucleases are members of the structure-specific, 5' nuclease family (FEN-like) that catalyzes hydrolysis of DNA duplex-containing nucleic acid structures during DNA replication, repair, and recombination. Canonical members of the FEN-like family possess a PIN domain with a two-helical structure insert (also known as the helical arch, helical clamp or I domain) of variable length (approximately 16 to 800 residues), and at the C-terminus of the PIN domain a H3TH (helix-3-turn-helix) domain, an atypical helix-hairpin-helix-2-like region. Both the H3TH domain (not included in this model) and the helical arch/clamp region are involved in DNA binding. The PIN domain belongs to a large nuclease superfamily. The structural properties of the PIN domain indicate its putative active center, consisting of invariant acidic amino acid residues (putative metal-binding residues), is geometrically similar in the active center of structure-specific 5' nucleases, PIN-domain ribonucleases of eukaryotic rRNA editing proteins, and bacterial toxins of toxin-antitoxin (TA) operons. In the T5-5'nuclease, structure-specific endonuclease activity requires binding of a single metal ion in the high-affinity, metal binding site 1, whereas exonuclease activity requires both, the high-affinity, metal binding site 1 and the low-affinity, metal binding site 2 to be occupied by a divalent cofactor. The T5-5'nuclease is reported to be able to bind several metal ions including, Mg2+, Mn2+, Zn2+ and Co2+, as co-factors.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1841998963   2 VVLAFTDDVNWRKVLVDETYKENRKATR----KPVGY----RDFLSKLWERDEFIHIKEDMLEGDDVMGIIGSGHEVFGF 73
Cdd:cd09860    47 KPIVLWDGRASWRKDLFPEYKANRKKTReekkAWREAfeaqRPFIEEALEYLGVPQIRAPGAEADDLAGVLVKRLAAFGD 126

                          90       100       110
                  ....*....|....*....|....*....|...
gi 1841998963  74 KkAVLVSCDKDFKTIPDVDFLWCTTGNILTQTK 106
Cdd:cd09860   127 K-VLLVSGDKDWLQLVYENVSWFSPITDKEVTL 158