RING finger (Really Interesting New Gene) domain and U-box domain superfamily; The RING finger is a specialized type of Zn-finger of 40 to 60 residues that binds two atoms of zinc. It is defined by the "cross-brace" motif that chelates zinc atoms by eight amino acid residues, typically Cys or His, arranged in a characteristic spacing. Canonical RING motifs have been categorized into two major subclasses, RING-HC (C3HC4-type) and RING-H2 (C3H2C3-type), according to their Cys/His content. There are also many variants of RING fingers: some have different Cys/His patterns while some lack a single Cys or His residue at typical Zn ligand positions (the fourth or eighth zinc ligand is prevalently exchanged for an Asp, which can indeed chelate Zn in a RING finger as well). C4C4-, C3HC3D-, C2H2C4-, and C3HC5-type RING fingers are closely related to RING-HC fingers. In contrast, C4HC3- (RING-CH alias RINGv), C3H3C2-, C3H2C2D-, C3DHC3-, and C4HC2H-type RING fingers are more closely related to RING-H2 fingers. However, not all RING finger-containing proteins display regular RING finger features, and the RING finger family has turned out to be multifarious. The degenerate RING fingers of the Siz/PIAS RING (SP-RING) family proteins and sporulation protein RMD5, are characterized by lacking the second, fifth, and sixth Zn2+ ion-coordinating residues. They bind only one Zn2+ ion. On the other hand, the RING fingers of the human APC11 and RBX1 proteins can bind a third Zn atom since they harbor four additional Zn ligands. U-box is a modified form of the RING finger domain that lacks metal chelating Cys and His residues. It resembles the cross-brace RING structure consisting of three beta-sheets and a single alpha-helix, which would be stabilized by salt bridges instead of chelated metal ions. U-box proteins are widely distributed among eukaryotic organisms and show a higher prevalence in plants than in other organisms. RING finger/U-box-containing proteins are a group of diverse proteins with a variety of cellular functions, including oncogenesis, development, viral replication, signal transduction, the cell cycle and apoptosis. Many of them are ubiquitin-protein ligases (E3s) that serve as scaffolds for binding to ubiquitin-conjugating enzymes (E2s, also referred to as ubiquitin carrier proteins or UBCs) in close proximity to substrate proteins, which enable efficient transfer of ubiquitin from E2 to the substrates.

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gi 767948755   1 MIPCKHVFCYDCAILHekkgDKMCPGCSDPVQRIEQCTRG 40
Cdd:cd16508   16 MIPCKHVFCLDCARLH----DKICPRCDDPVQRIEQCTRG 51

RING finger, HC subclass, found in E3 ubiquitin-protein ligase Hakai, zinc finger protein 645 (ZNF645), and similar proteins; Hakai, also known as Casitas B-lineage lymphoma-transforming sequence-like protein 1, RING finger protein 188 (RNF188), or c-Cbl-like protein 1 (CBLL1), is an E3 ubiquitin ligase that disrupts cell-cell contacts in epithelial cells and is upregulated in human colon and gastric adenocarcinomas. It was identified to mediate the posttranslational downregulation of E-cadherin (CDH1), a major component of adherens junctions in epithelial cells and a potent tumor suppressor. It also promotes ubiquitination of several other tyrosine-phosphorylated Src substrates, including cortactin (CTTN) and DOK1. Hakai acts as a homodimer arranged in an anti-parallel configuration with a novel HYB (Hakai pTyr-binding) domain that forms a phosphotyrosine-binding pocket. Each monomer contains a C3HC4-type RING-HC finger and a short pTyr-B domain that incorporates a novel, atypical C2H2-type Zn-finger coordination motif. Both domains are important for dimerization. ZNF645 is a novel testis-specific E3 ubiquitin-protein ligase that plays a role in sperm production and quality control. It has a structure similar to that of the c-Cbl-like protein Hakai. In contrast to Hakai, its HYB domain demonstrates different target specificities. It interacts with v-Src-phosphorylated E-cadherin, but not to cortactin.

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gi 767948755   1 MIPCKHVFCYDCAILHekkgDKMCPGCSDPVQRIEQCTRG 40
Cdd:cd16508   16 MIPCKHVFCLDCARLH----DKICPRCDDPVQRIEQCTRG 51

RING finger, HC subclass, found in E3 ubiquitin-protein ligase Hakai, zinc finger protein 645 (ZNF645), and similar proteins; Hakai, also known as Casitas B-lineage lymphoma-transforming sequence-like protein 1, RING finger protein 188 (RNF188), or c-Cbl-like protein 1 (CBLL1), is an E3 ubiquitin ligase that disrupts cell-cell contacts in epithelial cells and is upregulated in human colon and gastric adenocarcinomas. It was identified to mediate the posttranslational downregulation of E-cadherin (CDH1), a major component of adherens junctions in epithelial cells and a potent tumor suppressor. It also promotes ubiquitination of several other tyrosine-phosphorylated Src substrates, including cortactin (CTTN) and DOK1. Hakai acts as a homodimer arranged in an anti-parallel configuration with a novel HYB (Hakai pTyr-binding) domain that forms a phosphotyrosine-binding pocket. Each monomer contains a C3HC4-type RING-HC finger and a short pTyr-B domain that incorporates a novel, atypical C2H2-type Zn-finger coordination motif. Both domains are important for dimerization. ZNF645 is a novel testis-specific E3 ubiquitin-protein ligase that plays a role in sperm production and quality control. It has a structure similar to that of the c-Cbl-like protein Hakai. In contrast to Hakai, its HYB domain demonstrates different target specificities. It interacts with v-Src-phosphorylated E-cadherin, but not to cortactin.

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gi 767948755   1 MIPCKHVFCYDCAILHekkgDKMCPGCSDPVQRIEQCTRG 40
Cdd:cd16508   16 MIPCKHVFCLDCARLH----DKICPRCDDPVQRIEQCTRG 51

RING finger, HC subclass, found in Arabidopsis thaliana MND1-interacting protein 1 (MIP1) and similar proteins; This subfamily includes Arabidopsis thaliana MIP1, RING finger protein 4 (RF4) and RING finger protein 298 (RF298). MIP1 interacts with MND1, HOP2 and XRI1. RF4 and RF298 are putative E3 ubiquitin-protein ligase that may mediate E2-dependent protein ubiquitination. Members of this subfamily contain a typical C3HC4-type RING-HC finger.

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gi 767948755   2 IPCKH-VFCYDCAILHEKKGDKMCPGCSDPVQR 33
Cdd:cd23128   19 LPCAHqVVCSGCNDLHEKKGMRECPSCRGEIQE 51

RING finger, HC subclass, found in RING finger protein 10 (RNF10) and similar proteins; RNF10 is an E3 ubiquitin-protein ligase that interacts with mesenchyme Homeobox 2 (MEOX2) transcription factor, a regulator of the proliferation, differentiation and migration of vascular smooth muscle cells and cardiomyocytes; it enhances Meox2 activation of the p21 promoter. It also regulates the expression of myelin-associated glycoprotein (MAG) genes and is required for myelin production in Schwann cells of the peripheral nervous system. Moreover, RNF10 regulates retinoic acid-induced neuronal differentiation and the cell cycle exit of P19 embryonic carcinoma cells. RNF10 contains a C3HC4-type RING-HC finger and three putative nuclear localization signals.

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gi 767948755   1 MIPCKHVFCYDCaILH----EKKGDKMCPGCSDPVQRIE 35
Cdd:cd16536   15 ITRCGHIFCWPC-ILRylslSEKKWRKCPICFESIHKKD 52