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 686595016 303 AVCKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDFYAAH 367
Cdd:cd16736   33 SFCKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDFYAAH 97

RING finger found in polycomb group RING finger protein 4 (PCGF4) and similar proteins; PCGF4, also known as polycomb complex protein BMI-1 (B cell-specific Moloney murine leukemia virus integration site 1) or RING finger protein 51 (RNF51), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR). It serves as the core component of a canonical Polycomb repressive complex 1 (PRC1), which is composed of a chromodomain-containing protein (CBX2, CBX4, CBX6, CBX7 or CBX8) and a Polyhomeotic protein (PHC1, PHC2, or PHC3), and plays important roles in chromatin compaction and H2AK119 monoubiquitination. PCGF4 associates with the Runx1/CBFbeta transcription factor complex to silence target genes in a PRC2-independent manner. Moreover, PCGF4 is expressed in the hair cells and supporting cells. It can regulate cell survival by controlling mitochondrial function and reactive oxygen species (ROS) level in thymocytes and neurons, thus having an important role in the survival and sensitivity to ototoxic drug of auditory hair cells. Furthermore, PCGF4 controls memory CD4 T-cell survival through direct repression of Noxa gene in an Ink4a- and Arf-independent manner. It is required in neurons to suppress p53-induced apoptosis via regulating the antioxidant defensive response, and also involved in the tumorigenesis of various cancer types. PCGF4 contains a C3HC4-type RING-HC finger.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 686595016 303 AVCKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDFYAAH 367
Cdd:cd16736   33 SFCKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDFYAAH 97

RING finger- and WD40-associated ubiquitin-like (RAWUL) domain found in polycomb group RING finger protein 2 (PCGF2); PCGF2, also termed DNA-binding protein Mel-18, or RING finger protein 110 (RNF110), or zinc finger protein 144 (ZNF144), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) and serves as the core component of a canonical polycomb repressive complex 1 (PRC1), which is composed of a chromodomain-containing protein (CBX2, CBX4, CBX6, CBX7 or CBX8) and a polyhomeotic protein (PHC1, PHC2, or PHC3). Like other PCGF homologs, PCGF2 associates with ring finger protein 2 (RNF2) to form a RNF2-PCGF heterodimer, which is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. Moreover, PCGF2 uniquely regulates PRC1 to specify mesoderm cell fate in embryonic stem cells. It is required for PRC1 stability and maintenance of gene repression in embryonic stem cells (ESCs) and essential for ESC differentiation into early cardiac-mesoderm precursors. PCGF2 also plays a significant role in the angiogenic function of endothelial cells (ECs) by regulating endothelial gene expression. Furthermore, PCGF2 is a SUMO-dependent regulator of hormone receptors. It facilitates the deSUMOylation process by inhibiting PCGF4/BMI1-mediated ubiquitin-proteasomal degradation of SUMO1/sentrin-specific protease 1 (SENP1). It is also a novel negative regulator of breast cancer stem cells (CSCs) that inhibits the stem cell population, and in vitro and in vivo self-renewal through the inactivation of Wnt-mediated Notch signaling. PCGF2 contains a C3HC4-type RING-HC finger, and a RAWUL domain.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 686595016 396 IISLSIEFFDQNRLERKGNKEKE--KSKEEVNDKRYLRCPAAMTVMHLRKFLRSKMDIPNTFQIDVMYEEEPLKDYYTLM 473
Cdd:cd17164    1 IVSLSIEFYEGARDEKKQRPASPgdPFKEQRNGKRFLRCPAAMTVMHLAKFLRNKMDVPSKYRVEVLYEDEPLKDYYTLM 80

                         90
                 ....*....|....*....
gi 686595016 474 DIAYIYTWRRNGPLPLKYR 492
Cdd:cd17164   81 DIAYIYPWRRNGPLPLKYR 99

RING finger found in polycomb group RING finger protein 4 (PCGF4) and similar proteins; PCGF4, also known as polycomb complex protein BMI-1 (B cell-specific Moloney murine leukemia virus integration site 1) or RING finger protein 51 (RNF51), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR). It serves as the core component of a canonical Polycomb repressive complex 1 (PRC1), which is composed of a chromodomain-containing protein (CBX2, CBX4, CBX6, CBX7 or CBX8) and a Polyhomeotic protein (PHC1, PHC2, or PHC3), and plays important roles in chromatin compaction and H2AK119 monoubiquitination. PCGF4 associates with the Runx1/CBFbeta transcription factor complex to silence target genes in a PRC2-independent manner. Moreover, PCGF4 is expressed in the hair cells and supporting cells. It can regulate cell survival by controlling mitochondrial function and reactive oxygen species (ROS) level in thymocytes and neurons, thus having an important role in the survival and sensitivity to ototoxic drug of auditory hair cells. Furthermore, PCGF4 controls memory CD4 T-cell survival through direct repression of Noxa gene in an Ink4a- and Arf-independent manner. It is required in neurons to suppress p53-induced apoptosis via regulating the antioxidant defensive response, and also involved in the tumorigenesis of various cancer types. PCGF4 contains a C3HC4-type RING-HC finger.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 686595016 303 AVCKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDFYAAH 367
Cdd:cd16736   33 SFCKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDFYAAH 97

RRING finger- and WD40-associated ubiquitin-like (RAWUL) domain found in PCGF1-6, RING1 and -2, DRIP and similar proteins; structurally similar to a beta-grasp ubiquitin-like fold; The family includes six Polycomb Group (PcG) RING finger homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) that use epigenetic mechanisms to maintain or repress expression of their target genes. They were first discovered in fruit flies that can remodel chromatin such that epigenetic silencing of genes takes place, and are well known for silencing Hox genes through modulation of chromatin structure during embryonic development in fruit flies. PCGF homologs play important roles in cell proliferation, differentiation, and tumorigenesis. They all have been found to associate with ring finger protein 2 (RNF2). The RNF2-PCGF heterodimer is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. Moreover, PCGF homologs are critical components in the assembly of distinct Polycomb Repression Complex 1 (PRC1) related complexes which are involved in the maintenance of gene repression and target different genes through distinct mechanisms. The Drosophila PRC1 core complex is formed by the Polycomb (Pc), Polyhomeotic (Ph), Posterior sex combs (Psc), and Sex combs extra (Sce, also known as Ring) subunits. In mammals, the composition of PRC1 is much more diverse and varies depending on the cellular context. All PRC1 complexes contain homologs of the Drosophila Ring protein. Ring1A/RNF1 and Ring1B/RNF2 are E3 ubiquitin ligases that mark lysine 119 of histone H2A with a single ubiquitin group (H2AK119ub). Mammalian homologs of the Drosophila Psc protein, such as PCGF2/Mel-18 or PCGF4/BMI1, regulate PRC1 enzymatic activity. PRC1 complexes can be divided into at least two classes according to the presence or absence of CBX proteins, which are homologs of Drosophila Pc. Canonical PRC1 complexes contain CBX proteins that recognize and bind H3K27me3, the mark deposited by PRC2. Therefore, canonical PRC1 complexes and PRC2 can act together to repress gene transcription and maintain this repression through cell division. Non-canonical PRC1 complexes, containing RYBP (together with additional proteins, such as L3mbtl2 or Kdm2b) rather than the CBX proteins, have recently been described in mammals. PCGF homologs contain a C3HC4-type RING-HC finger, and a RAWUL domain that might be responsible for interaction with Cbx members of the Polycomb repression complexes.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 686595016 396 IISLSIEFFDQNRLERKGnkekekskeeVNDKRYLRCPAAMTVMHLRKFLRSKMDIPNTFQIDVMYEEEPLKDYYTLMDI 475
Cdd:cd16102    1 QVSLSLEPSESNLGGKLP----------QLEKPYLRCSARATVGHLKKFLRRKLKLDSEQDLDILCRGELLGKEHTLKFI 70

                         90
                 ....*....|....*..
gi 686595016 476 AYIYTWRRNGPLPLKYR 492
Cdd:cd16102   71 WRTRWRKQDGPLVLQYR 87

RING finger found in polycomb group RING finger protein 5 (PCGF5) and similar proteins; PCGF5, also known as RING finger protein 159 (RNF159), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) and serves as the core component of a Polycomb repressive complex 1 (PRC1). Like other PCGF homologs, PCGF5 associates with ring finger protein 2 (RNF2) to form a RNF2-PCGF heterodimer, which is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. PCGF5 contains a C3HC4-type RING-HC finger.

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                 ....*....|....*....|....*....|....*....|....*....|....*....
gi 686595016 305 CKTCIVRYLETSKYCPICDVQVHKTRPLLNIRSDKTLQDIVYKLVPGLFKNEMKRRRDF 363
Cdd:cd16737   34 CKSCIVQHFEDSNDCPECGIQVHETNPLEMLRLDNTLEEIIFKLVPGLRERELQREAEF 92

RING finger- and WD40-associated ubiquitin-like (RAWUL) domain found in polycomb group RING finger protein 1 (PCGF1) and similar proteins; PCGF1, also termed nervous system Polycomb-1 (NSPc1), or RING finger protein 68 (RNF68), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) and serves as the core component of a noncanonical Polycomb repressive complex 1 (PRC1)-like BCOR complex that also contains RING1, RNF2, RYBP, SKP1, as well as the BCL6 co-repressor BCOR and the histone demethylase KDM2B, and is required to maintain the transcriptionally repressive state of some genes, such as Hox genes, BCL6 and the cyclin-dependent kinase inhibitor, CDKN1A. PCGF1 promotes cell cycle progression and enhances cell proliferation as well. It is a cell growth regulator that acts as a transcriptional repressor of p21Waf1/Cip1 via the retinoid acid response element (RARE element). Moreover, PCGF1 functions as an epigenetic regulator involved in hematopoietic cell differentiation. It cooperates with the transcription factor runt-related transcription factor 1 (Runx1) in regulating differentiation and self-renewal of hematopoietic cells. Furthermore, PCGF1 represents a physical and functional link between Polycomb function and pluripotency. PCGF1 contains a C3HC4-type RING-HC finger and a RAWUL domain.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 686595016 394 DEIISLSieffdqnrLERKGNKEKEKSK-EEVNDKRYLRCPAAMTVMHLRKFLRSKMDIPNTFQIDVMYEEEPLKDYYTL 472
Cdd:cd17081    1 DEQVSLC--------LERLSSGKSSKDKnKKPLQRKYVRCSVRAEVRHLKKLLRKKLAVPPLQQVQILCNNEVLPDHMTM 72

                         90       100
                 ....*....|....*....|.
gi 686595016 473 MDIaYIYTWR-RNGPLPLKYR 492
Cdd:cd17081   73 KQI-WLSHWFgKAPPLVLHYS 92

RING finger- and WD40-associated ubiquitin-like (RAWUL) domain found in polycomb group RING finger protein 5 (PCGF5) and similar proteins; PCGF5, also termed RING finger protein 159 (RNF159), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) and serves as the core component of a Polycomb repressive complex 1 (PRC1). Like other PCGF homologs, PCGF5 associates with ring finger protein 2 (RNF2) to form a RNF2-PCGF heterodimer, which is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. PCGF5 contains a C3HC4-type RING-HC finger, and a RAWUL domain.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 686595016 427 KRYLRCPAAMTVMHLRKFLRSKMDIPNTFQIDVMYEEEPLKDYYTlMDIAYIYTWRRNG----PLPLKYRVR 494
Cdd:cd17084   27 KKFIRCSSRVTVGTIKKFLSLKLKLPSSYELDVLCNGEIMGKDHT-LEFIYMTRWRLRGensyPMVLQYRPR 97

RING finger, HC subclass, found in Polycomb Group RING finger homologs (PCGF1, 2, 3, 4, 5 and 6), and similar proteins; This subfamily includes six Polycomb Group (PcG) RING finger homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) that use epigenetic mechanisms to maintain or repress expression of their target genes. They were first discovered in fruit flies and are well known for silencing Hox genes through modulation of chromatin structure during embryonic development. PCGF homologs play important roles in cell proliferation, differentiation, and tumorigenesis. They all have been found to associate with ring finger protein 2 (RNF2). The RNF2-PCGF heterodimer is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. Moreover, PCGF homologs are critical components in the assembly of distinct Polycomb Repression Complex 1 (PRC1) related complexes which is involved in the maintenance of gene repression and which target different genes through distinct mechanisms. The Drosophila PRC1 core complex is formed by the Polycomb (Pc), Polyhomeotic (Ph), Posterior sex combs (Psc), and Sex combs extra (Sce, also known as Ring) subunits. In mammals, the composition of PRC1 is much more diverse and varies depending on the cellular context. All PRC1 complexes contain homologs of the Drosophila Ring protein. Ring1A/RNF1 and Ring1B/RNF2 are E3 ubiquitin ligases that mark lysine 119 of histone H2A with a single ubiquitin group (H2AK119ub). Mammalian homologs of the Drosophila Psc protein, such as PCGF2/Mel-18 or PCGF4/BMI1, regulate PRC1 enzymatic activity. PRC1 complexes can be divided into at least two classes according to the presence or absence of CBX proteins, which are homologs of Drosophila Pc. Canonical PRC1 complexes contain CBX proteins that recognize and bind H3K27me3, the mark deposited by PRC2. Therefore, canonical PRC1 complexes and PRC2 can act together to repress gene transcription and maintain this repression through cell division. Non-canonical PRC1 complexes, containing RYBP (together with additional proteins, such as L3mbtl2 or Kdm2b) rather than the CBX proteins have recently been described in mammals. PCGF homologs contain a C3HC4-type RING-HC finger.

                         10
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gi 686595016 305 CKTCIVRYLETSKYCPICD 323
Cdd:cd16525   24 CKSCIVRHLETSKNCPVCD 42

RING finger found in polycomb group RING finger protein 3 (PCGF3) and similar proteins; PCGF3, also known as RING finger protein 3A (RNF3A), is one of six PcG RING finger (PCGF) homologs (PCGF1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6) and serves as the core component of a Polycomb repressive complex 1 (PRC1). Like other PCGF homologs, PCGF3 associates with ring finger protein 2 (RNF2) to form a RNF2-PCGF heterodimer, which is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. PCGF3 contains a C3HC4-type RING-HC finger.

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                 ....*....|....*....|....*....|..
gi 686595016 305 CKTCIVRYLETSKYCPICDVQVHKTRPLLNIR 336
Cdd:cd16735   35 CKSCLVKYLEENNTCPTCGIVIHQSHPLQYIG 66