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 808358728   1 MYCPSGDKCPLVGSAMPWAFMQG 23
Cdd:cd16716   45 VYCPSGEKCPLVGSNVPWAFMQG 67

variant of RING finger, HC subclass, found in interferon regulatory factor 2 (IRF2)-binding protein 2 (IRF-2BP2); IRF-2BP2, also known as IRF-2-binding protein 2 or DIF-1, is a nuclear protein that binds to the C-terminal repression domain of IRF-2 and acts as an IRF-2-dependent transcriptional corepressor, both enhancer-activated and basal transcription. IRF-2BP2 also specifically interacts with the C-terminal domain of the nuclear factor of activated T cells NFAT1 transcription factor, and negatively regulates the NFAT1-dependent transactivation of NFAT-responsive promoters. Moreover, IRF2BP2 suppresses the transactivation activity of p53 on both Bax and p21 promoters. It also shows anti-apoptotic activity through the modulation of the death domain in NRIF3. In addition, IRF2BP2 functions as a cofactor of VGLL4 and plays a critical role controlling gene expression in skeletal, cardiac, and smooth muscle cells. It is a muscle-enriched transcription factor required to activate vascular endothelial growth factor-A (VEGF-A) expression. IRF-2BP2 contains an N-terminal C4-type zinc finger and a C-terminal variant C3HC4-type RING-HC finger. The zinc finger is responsible for the homo- and hetero-dimerization between different members of the IRF-2BP2 family. The RING-HC finger interacts with IRF2 and also with nuclear receptor interacting factor 3 (NRIF3).

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gi 808358728   1 MYCPSGDKCPLVGSAMPWAFMQG 23
Cdd:cd16716   45 VYCPSGEKCPLVGSNVPWAFMQG 67

variant of RING finger, HC subclass, found in interferon regulatory factor 2 (IRF2)-binding protein 2 (IRF-2BP2); IRF-2BP2, also known as IRF-2-binding protein 2 or DIF-1, is a nuclear protein that binds to the C-terminal repression domain of IRF-2 and acts as an IRF-2-dependent transcriptional corepressor, both enhancer-activated and basal transcription. IRF-2BP2 also specifically interacts with the C-terminal domain of the nuclear factor of activated T cells NFAT1 transcription factor, and negatively regulates the NFAT1-dependent transactivation of NFAT-responsive promoters. Moreover, IRF2BP2 suppresses the transactivation activity of p53 on both Bax and p21 promoters. It also shows anti-apoptotic activity through the modulation of the death domain in NRIF3. In addition, IRF2BP2 functions as a cofactor of VGLL4 and plays a critical role controlling gene expression in skeletal, cardiac, and smooth muscle cells. It is a muscle-enriched transcription factor required to activate vascular endothelial growth factor-A (VEGF-A) expression. IRF-2BP2 contains an N-terminal C4-type zinc finger and a C-terminal variant C3HC4-type RING-HC finger. The zinc finger is responsible for the homo- and hetero-dimerization between different members of the IRF-2BP2 family. The RING-HC finger interacts with IRF2 and also with nuclear receptor interacting factor 3 (NRIF3).

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gi 808358728   1 MYCPSGDKCPLVGSAMPWAFMQG 23
Cdd:cd16716   45 VYCPSGEKCPLVGSNVPWAFMQG 67

variant of RING finger, HC subclass, found in interferon regulatory factor 2-binding protein-like (IRF-2BPL); IRF-2BPL, also known as C14orf4 or enhanced at puberty protein 1(EAP1), is a homolog of interferon regulatory factor 2-binding proteins, IRF-2BP1 and IRF-2BP2. It is expressed in the mediobasal hypothalamus and plays a critical function in regulating the female reproductive neuroendocrine axis. IRF-2BPL is a proline-rich protein with polyglutamine and polyalanine tracks at the N-terminus and a C3HC4-type RING-HC finger domain with a partially new pattern at the C-terminus.

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gi 808358728   1 MYCPSGDKCPLVGSAMPW 18
Cdd:cd16717   49 VYCPSGEKCPLVGSNVPW 66