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 392889767  906 CSHCARPISGRAFNVHSCRHFFHRECLeiamisflsqeevekmktliideervlsqmkaeqlagnqkgfiekqekylkIA 985
Cdd:cd16462     3 CAVCGRPLLTRQFYVFPCQHAFHADCL---------------------------------------------------IE 31

                          90
                  ....*....|....*....
gi 392889767  986 AFISNIVGAECPLCGNIAI 1004
Cdd:cd16462    32 EVLDDLIASECPLCGELMI 50

RING finger, H2 subclass, found in Saccharomyces cerevisiae vacuolar membrane protein PEP3 (Pep3p) and similar proteins; Pep3p, also known as carboxypeptidase Y-deficient protein 3, vacuolar morphogenesis protein 8, vacuolar protein sorting-associated protein 18 (Vps18p), or vacuolar protein-targeting protein 18, is a vacuolar membrane protein that affects late Golgi functions required for vacuolar protein sorting and efficient alpha-factor prohormone maturation. It is required for vacuolar biogenesis and for trafficking of hydrolase precursors to the vacuole. The disruption of PEP3 may cause hypersensitivity to heat shock and ethanol stresses, probably due to disappearance of normal vacuoles. As a component of the homotypic fusion and vacuole protein sorting (HOPS) and class C core vacuole/endosome tethering (CORVET) complexes, its overexpression shortens lag phase but does not alter growth rate in Saccharomyces cerevisiae exposed to acetic acid stress. Moreover, Pep3p forms the Class C Vps protein complex (C-Vps complex) with Pep5p (also known as Vps11), Vps16, and Vps33, and is necessary for trafficking of hydrolase precursors to the vacuole by promoting vesicular docking reactions with SNARE proteins. Pep3p contains a C3H2C3-type RING-H2 finger at the C-terminus.

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                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 392889767  906 CSHCARPISGRAFNVHSCRHFFHRECLeiamisflsqeevekmktliideervlsqmkaeqlagnqkgfiekqekylkIA 985
Cdd:cd16462     3 CAVCGRPLLTRQFYVFPCQHAFHADCL---------------------------------------------------IE 31

                          90
                  ....*....|....*....
gi 392889767  986 AFISNIVGAECPLCGNIAI 1004
Cdd:cd16462    32 EVLDDLIASECPLCGELMI 50

RING finger, H2 subclass, found in Saccharomyces cerevisiae vacuolar membrane protein PEP3 (Pep3p) and similar proteins; Pep3p, also known as carboxypeptidase Y-deficient protein 3, vacuolar morphogenesis protein 8, vacuolar protein sorting-associated protein 18 (Vps18p), or vacuolar protein-targeting protein 18, is a vacuolar membrane protein that affects late Golgi functions required for vacuolar protein sorting and efficient alpha-factor prohormone maturation. It is required for vacuolar biogenesis and for trafficking of hydrolase precursors to the vacuole. The disruption of PEP3 may cause hypersensitivity to heat shock and ethanol stresses, probably due to disappearance of normal vacuoles. As a component of the homotypic fusion and vacuole protein sorting (HOPS) and class C core vacuole/endosome tethering (CORVET) complexes, its overexpression shortens lag phase but does not alter growth rate in Saccharomyces cerevisiae exposed to acetic acid stress. Moreover, Pep3p forms the Class C Vps protein complex (C-Vps complex) with Pep5p (also known as Vps11), Vps16, and Vps33, and is necessary for trafficking of hydrolase precursors to the vacuole by promoting vesicular docking reactions with SNARE proteins. Pep3p contains a C3H2C3-type RING-H2 finger at the C-terminus.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 392889767  906 CSHCARPISGRAFNVHSCRHFFHRECLeiamisflsqeevekmktliideervlsqmkaeqlagnqkgfiekqekylkIA 985
Cdd:cd16462     3 CAVCGRPLLTRQFYVFPCQHAFHADCL---------------------------------------------------IE 31

                          90
                  ....*....|....*....
gi 392889767  986 AFISNIVGAECPLCGNIAI 1004
Cdd:cd16462    32 EVLDDLIASECPLCGELMI 50