H3TH domains of structure-specific 5' nucleases (or flap endonuclease-1-like) involved in DNA replication, repair, and recombination; The 5' nucleases of this superfamily are capable of both 5'-3' exonucleolytic activity and cleaving bifurcated or branched DNA, in an endonucleolytic, structure-specific manner, and are involved in DNA replication, repair, and recombination. The superfamily includes the H3TH (helix-3-turn-helix) domains of Flap Endonuclease-1 (FEN1), Exonuclease-1 (EXO1), Mkt1, Gap Endonuclease 1 (GEN1) and Xeroderma pigmentosum complementation group G (XPG) nuclease. Also included are the H3TH domains of the 5'-3' exonucleases of DNA polymerase I and single domain protein homologs, as well as, the bacteriophage T4 RNase H, T5-5'nuclease, and other homologs. These nucleases contain a PIN (PilT N terminus) domain with a helical arch/clamp region/I domain (not included here) and inserted within the C-terminal region of the PIN domain is an atypical helix-hairpin-helix-2 (HhH2)-like region. This atypical HhH2 region, the H3TH domain, has an extended loop with at least three turns between the first two helices, and only three of the four helices appear to be conserved. Both the H3TH domain and the helical arch/clamp region are involved in DNA binding. Studies suggest that a glycine-rich loop in the H3TH domain contacts the phosphate backbone of the template strand in the downstream DNA duplex. Typically, the nucleases within this superfamily have a carboxylate rich active site that is involved in binding essential divalent metal ion cofactors (i. e., Mg2+, Mn2+, Zn2+, or Co2+) required for nuclease activity. The first metal binding site is composed entirely of Asp/Glu residues from the PIN domain, whereas, the second metal binding site is composed generally of two Asp residues from the PIN domain and one or two Asp residues from the H3TH domain. Together with the helical arch and network of amino acids interacting with metal binding ions, the H3TH region defines a positively charged active-site DNA-binding groove in structure-specific 5' nucleases.

                        10        20
                ....*....|....*....|....*.
gi 461694116  1 IDLIRQHGSIEEILENIDTSKHPAPE 26
Cdd:cd09907  27 LKLIKKHKSIEKILENIDKSKYPVPE 52

H3TH domain of Flap Endonuclease-1, a structure-specific, divalent-metal-ion dependent, 5' nuclease: Eukaryotic homologs; Members of this subgroup include the H3TH (helix-3-turn-helix) domains of eukaryotic Flap endonuclease-1 (FEN1), 5' nucleases. 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. These nucleases contain a PIN (PilT N terminus) domain with a helical arch/clamp region/I domain (not included here) and inserted within the PIN domain is an atypical helix-hairpin-helix-2 (HhH2)-like region. This atypical HhH2 region, the H3TH domain, has an extended loop with at least three turns between the first two helices, and only three of the four helices appear to be conserved. Both the H3TH domain and the helical arch/clamp region are involved in DNA binding. Studies suggest that a glycine-rich loop in the H3TH domain contacts the phosphate backbone of the template strand in the downstream DNA duplex. The nucleases within this subfamily have a carboxylate rich active site that is involved in binding essential divalent metal ion cofactors (Mg2+ or Mn2+) required for nuclease activity. The first metal binding site is composed entirely of Asp/Glu residues from the PIN domain, whereas, the second metal binding site is composed generally of two Asp residues from the PIN domain and one Asp residue from the H3TH domain. Together with the helical arch and network of amino acids interacting with metal binding ions, the H3TH region defines a positively charged active-site DNA-binding groove in structure-specific 5' nucleases. Also, 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.

                        10        20
                ....*....|....*....|....*.
gi 461694116  1 IDLIRQHGSIEEILENIDTSKHPAPE 26
Cdd:cd09907  27 LKLIKKHKSIEKILENIDKSKYPVPE 52

5'-3' exonuclease, C-terminal SAM fold;

                         10        20
                 ....*....|....*....|....
gi 461694116   1 IDLIRQHGSIEEILENIDTSKHPA 24
Cdd:pfam01367 32 AKLLNEYGSLENILANADEIKGGK 55

5'-3' exonuclease;

                           10
                   ....*....|....*...
gi 461694116     1 IDLIRQHGSIEEILENID 18
Cdd:smart00475 200 AKLLKEFGSLENILENLD 217

H3TH domain of Flap Endonuclease-1, a structure-specific, divalent-metal-ion dependent, 5' nuclease: Eukaryotic homologs; Members of this subgroup include the H3TH (helix-3-turn-helix) domains of eukaryotic Flap endonuclease-1 (FEN1), 5' nucleases. 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. These nucleases contain a PIN (PilT N terminus) domain with a helical arch/clamp region/I domain (not included here) and inserted within the PIN domain is an atypical helix-hairpin-helix-2 (HhH2)-like region. This atypical HhH2 region, the H3TH domain, has an extended loop with at least three turns between the first two helices, and only three of the four helices appear to be conserved. Both the H3TH domain and the helical arch/clamp region are involved in DNA binding. Studies suggest that a glycine-rich loop in the H3TH domain contacts the phosphate backbone of the template strand in the downstream DNA duplex. The nucleases within this subfamily have a carboxylate rich active site that is involved in binding essential divalent metal ion cofactors (Mg2+ or Mn2+) required for nuclease activity. The first metal binding site is composed entirely of Asp/Glu residues from the PIN domain, whereas, the second metal binding site is composed generally of two Asp residues from the PIN domain and one Asp residue from the H3TH domain. Together with the helical arch and network of amino acids interacting with metal binding ions, the H3TH region defines a positively charged active-site DNA-binding groove in structure-specific 5' nucleases. Also, 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.

                        10        20
                ....*....|....*....|....*.
gi 461694116  1 IDLIRQHGSIEEILENIDTSKHPAPE 26
Cdd:cd09907  27 LKLIKKHKSIEKILENIDKSKYPVPE 52

H3TH domains of Flap endonuclease-1 (FEN1)-like structure specific 5' nucleases: FEN1 (eukaryotic) and EXO1; The 5' nucleases within this family are capable of both 5'-3' exonucleolytic activity and cleaving bifurcated or branched DNA, in an endonucleolytic, structure-specific manner, and are involved in DNA replication, repair, and recombination. This family includes the H3TH (helix-3-turn-helix) domains of eukaryotic Flap Endonuclease-1 (FEN1), Exonuclease-1 (EXO1), and other eukaryotic homologs. These nucleases contain a PIN (PilT N terminus) domain with a helical arch/clamp region/I domain (not included here) and inserted within the PIN domain is an atypical helix-hairpin-helix-2 (HhH2)-like region. This atypical HhH2 region, the H3TH domain, has an extended loop with at least three turns between the first two helices, and only three of the four helices appear to be conserved. Both the H3TH domain and the helical arch/clamp region are involved in DNA binding. Studies suggest that a glycine-rich loop in the H3TH domain contacts the phosphate backbone of the template strand in the downstream DNA duplex. The nucleases within this family have a carboxylate rich active site that is involved in binding essential divalent metal ion cofactors (i. e., Mg2+, Mn2+, Zn2+, or Co2+) required for nuclease activity. The first metal binding site is composed entirely of Asp/Glu residues from the PIN domain, whereas, the second metal binding site is composed generally of two Asp residues from the PIN domain and one Asp residue from the H3TH domain. Together with the helical arch and network of amino acids interacting with metal binding ions, the H3TH region defines a positively charged active-site DNA-binding groove in structure-specific 5' nucleases.

                        10        20
                ....*....|....*....|....*..
gi 461694116  3 LIRQHGSIEEILENIDTSKH---PAPE 26
Cdd:cd09901  29 LIKKHKSIEKVLKALRSNKKkkvPVPY 55

5'-3' exonuclease Xni/ExoIX (flap endonuclease) [Replication, recombination and repair];

                         10
                 ....*....|....*...
gi 461694116   1 IDLIRQHGSIEEILENID 18
Cdd:COG0258  204 AKLLQEYGSLENILANAD 221

5'-3' exonuclease;

                           10
                   ....*....|....*...
gi 461694116     1 IDLIRQHGSIEEILENID 18
Cdd:smart00475 200 AKLLKEFGSLENILENLD 217