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Query: EC:6.3.2.19 (ubiquitin-protein ligase)
 799 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several genes, including RPS4X (ribosomal protein subunit 4), ZFX (zinc finger on the X chromosome), and UBE1 (ubiquitin-activating enzyme), have been shown to be expressed from the inactive X chromosome of cultured human cells. By contrast, these genes are subject to X-chromosome inactivation in tissues from adult mice. We have now examined the inactivation status of these genes in cultured mouse cells to determine whether the differences in X-chromosome inactivation between species is due to an intrinsic difference between human and mouse X-chromosome genes or whether it is a function of gene reactivation in cell culture per se. The expression of three mouse X-chromosome genes, Rps4, Zfx, and Ube1 was examined by reverse transcriptase polymerase chain reaction (RT-PCR) in heterozygous cultured cells from a cross of a laboratory mouse by Mus spretus, which were selected to uniformly express the X chromosome from the laboratory mouse parent. No expression of the M. spretus alleles of these genes was observed in the cell line (Hobmski), which is consistent with the patterns of expression previously observed in mouse in vivo and indicates that these genes remain stably inactivated in an immortalized mouse cell line. By cytogenetic and RT-PCR analyses the Hobmski cell line was shown to retain a late-replicating X chromosome from M. spretus, which expressed the M. spretus allele of the X (inactive) specific transcript (Xist). The Hobmski cell line will be a useful resource for studying the features that maintain X-chromosome genes inactive.
Somat Cell Mol Genet 1993 Jan
PMID:Maintenance of X inactivation of the Rps4, Zfx, and Ube1 genes in a mouse in vitro system. 768 8

The ubiquitin-protein conjugation system is involved in a variety of eukaryotic cell functions, including the degradation of abnormal and short-lived proteins, chromatin structure, cell cycle progression, and DNA repair. The ubiquitination of target proteins is catalyzed by a ubiquitin-activating enzyme (E1) and ubiquitin-conjugating enzymes (E2s) and in some cases also requires auxiliary substrate recognition proteins (E3s). Multiple E2s have been found, and these likely possess specificity for different classes of target proteins. Here we report the cloning and characterization of a gene (ubc-2) encoding a ubiquitin-conjugating enzyme which is involved in the selective degradation of abnormal and short-lived proteins in the nematode Caenorhabditis elegans. The nematode ubc-2 gene encodes a 16.7-kDa protein with striking amino acid sequence similarity to Saccharomyces cerevisiae UBC4 and UBC5 and Drosophila UbcD1. When driven by the UBC4 promoter, ubc-2 can functionally substitute for UBC4 in yeast cells; it rescues the slow-growth phenotype of ubc4 ubc5 mutants at normal temperature and restores their ability to grow at elevated temperatures. Western blots (immunoblots) of ubc4 ubc5 yeast cells transformed with ubc-2 reveal a protein of the expected size, which cross-reacts with anti-Drosophila UbcD1 antibody. C. elegans ubc-2 is constitutively expressed at all life cycle stages and, unlike yeast UBC4 and UBC5, is not induced by heat shock. Both trans and cis splicing are involved in the maturation of the ubc-2 transcript. These data suggest that yeast UBC4 and UBC5, Drosophila UbcD1, and C. elegans ubc-2 define a highly conserved gene family which plays fundamental roles in all eukaryotic cells.
Mol Cell Biol 1993 Mar
PMID:The ubc-2 gene of Caenorhabditis elegans encodes a ubiquitin-conjugating enzyme involved in selective protein degradation. 844 82

The transcription factor c-Fos is a short-lived cellular protein. The levels of the protein fluctuate significantly and abruptly during changing pathophysiological conditions. Thus, it is clear that degradation of the protein plays an important role in its tightly regulated activity. We examined the involvement of the ubiquitin pathway in c-Fos breakdown. Using a mutant cell line, ts20, that harbors a thermolabile ubiquitin-activating enzyme, E1, we demonstrate that impaired function of the ubiquitin system stabilizes c-Fos in vivo. In vitro, we reconstituted a cell-free system and demonstrated that the protein is multiply ubiquitinated. The adducts serve as essential intermediates for degradation by the 26S proteasome. We show that both conjugation and degradation are significantly stimulated by c-Jun, with which c-Fos forms the active heterodimeric transcriptional activator AP-1. Analysis of the enzymatic cascade involved in the conjugation process reveals that the ubiquitin-carrier protein E2-F1 and its human homolog UbcH5, which target the tumor suppressor p53 for degradation, are also involved in c-Fos recognition. The E2 enzyme acts along with a novel species of ubiquitin-protein ligase, E3. This enzyme is distinct from other known E3s, including E3 alpha/UBR1, E3 beta, and E6-AP. We have purified the novel enzyme approximately 350-fold and demonstrated that it is a homodimer with an apparent molecular mass of approximately 280 kDa. It contains a sulfhydryl group that is essential for its activity, presumably for anchoring activated ubiquitin as an intermediate thioester prior to its transfer to the substrate. Taken together, our in vivo and in vitro studies strongly suggest that c-Fos is degraded in the cell by the ubiquitin-proteasome proteolytic pathway in a process that requires a novel recognition enzyme.
Mol Cell Biol 1995 Dec
PMID:Degradation of the proto-oncogene product c-Fos by the ubiquitin proteolytic system in vivo and in vitro: identification and characterization of the conjugating enzymes. 852 78

When yeast cells growing on a poor nitrogen source are supplied with NH4+ ions, several nitrogen permeases including the general amino acid permease (Gap1p) are rapidly and completely inactivated. This report shows that inactivation by NH4+ of the Gap1 permease is accompanied by its degradation. A functional NPl1 gene product is required for both inactivation and degradation of Gap1p. Molecular analysis of the NPl1 gene showed that it is identical to RSP5. The RSP5 product is a ubiquitin-protein ligase (E3 enzyme) whose physiological function was, however, unknown. Its C-terminal region is very similar to that of other members of the E6-AP-like family of ubiquitin-protein ligases. Its N-terminal region contains a single C2 domain that may be a Ca(2+)-dependent phospholipid interaction motif, followed by several copies of a recently identified domain called WW(P). The Npi1/Rsp5 protein has a homologue both in humans and in mice, the latter being involved in brain development. Stress-induced degradation of the uracil permease (Fur4p), a process in which ubiquitin is probably involved, was also found to require a functional NPl1/RSP5 product. Chromosomal deletion of NPl1/RSP5 showed that this gene is essential for cell viability. In the viable npi1/rsp5 strain, expression of NPl1/RSP5 is reduced as a result of insertion of a Ty1 element in its 5' region. Our results show that the Npi1/Rsp5 ubiquitin-protein ligase participates in induced degradation of at least two permeases, Gap1p and Fur4p, and probably also other proteins.
Mol Microbiol 1995 Oct
PMID:NPl1, an essential yeast gene involved in induced degradation of Gap1 and Fur4 permeases, encodes the Rsp5 ubiquitin-protein ligase. 859 62

The abundance of B-type cyclin-CDK complexes is determined by regulated synthesis and degradation of cyclin subunits. Cyclin proteolysis is required for the final exit from mitosis and for the initiation of a new cell cycle. In extracts from frog or clam eggs, degradation is accompanied by ubiquitination of cyclin. Three genes, CDC16, CDC23, and CSE1 have recently been shown to be required specifically for cyclin B proteolysis in yeast. To test whether these genes are required for cyclin ubiquitination, we prepared extracts from G1-arrested yeast cells capable of conjugating ubiquitin to the B-type cyclin Clb2. The ubiquitination activity was cell cycle regulated, required Clb2's destruction box, and was low if not absent in cdc16, cdc23, cdc27, and cse1 mutants. Furthermore all these mutants were also defective in ubiquitination of another mitotic B-type cyclin, Clb3. The Cdc16, Cdc23, and Cdc27 proteins all contain several copies of the tetratricopeptide repeat and are subunits of a complex that is required for the onset of anaphase. The finding that gene products that are required for ubiquitination of Clb2 and Clb3 are also required for cyclin proteolysis in vivo provides the best evidence so far that cyclin B is degraded via the ubiquitin pathway in living cells. Xenopus homologues of Cdc16 and Cdc27 have meanwhile been shown to be associated with a 20S particle that appears to function as a cell cycle-regulated ubiquitin-protein ligase.
Mol Biol Cell 1996 May
PMID:TPR proteins required for anaphase progression mediate ubiquitination of mitotic B-type cyclins in yeast. 874 51

In temperature-sensitive (ts) mutants of mouse FM3A cells, the levels of mutagenesis and survival of cells treated with DNA-damaging agents have been difficult to assess because they are killed after their mutant phenotypes are expressed at the nonpermissive temperature. To avoid this difficulty, we incubated the ts mutant cells at the restrictive temperature, 39 degrees C, for only a limited period after inducing DNA damage. We used ts mutants defective in genes for ubiquitin-activating enzyme (E1), DNA polymerase alpha, and p34(cdc2) kinase. Whereas the latter two showed no effect, E1 mutants were sensitized remarkably to UV light if incubated at 39 degrees C for limited periods after UV exposure. Eighty-five percent of the sensitization occurred within the first 12 h of incubation at 39 degrees C, and more than 36 h at 39 degrees C did not produce any further sensitization. Moreover, while the 39 degrees C incubation gave E1 mutants a moderate spontaneous mutator phenotype, the same treatment significantly diminished the level of UV-induced 6-thioguanine resistance mutagenesis and extended the time necessary for expression of the mutation phenotype. These characteristics of E1 mutants are reminiscent of the defective DNA repair phenotypes of Saccharomyces cerevisiae rad6 mutants, which have defects in a ubiquitin-conjugating enzyme (E2), to which E1 is known to transfer ubiquitin. These results demonstrate the involvement of E1 in eukaryotic DNA repair and mutagenesis and provide the first direct evidence that the ubiquitin-conjugation system contributes to DNA repair in mammalian cells.
Mol Cell Biol 1997 Mar
PMID:Incubation at the nonpermissive temperature induces deficiencies in UV resistance and mutagenesis in mouse mutant cells expressing a temperature-sensitive ubiquitin-activating enzyme (E1). 903 76

The general amino acid permease, Gap1, of Saccharomyces cerevisiae is very active in cells grown on proline as the sole nitrogen source. Adding NH4+ to the medium triggers inactivation and degradation of the permease via a regulatory process involving Npi1p/Rsp5p, a ubiquitin-protein ligase. In this study, we describe several mutations affecting the C-terminal region of Gap1p that render the permease resistant to NH4(+)-induced inactivation. An in vivo isolated mutation (gap1pgr) causes a single Glu-->Lys substitution in an amino acid context similar to the DXKSS sequence involved in ubiquitination and endocytosis of the yeast alpha-factor receptor, Ste2p. Another replacement, substitution of two alanines for a di-leucine motif, likewise protects the Gap1 permease against NH4(+)-induced inactivation. In mammalian cells, such a motif is involved in the internalization of several cell-surface proteins. These data provide the first indication that a di-leucine motif influences the function of a plasma membrane protein in yeast. Mutagenesis of a putative phosphorylation site upstream from the di-leucine motif altered neither the activity nor the regulation of the permease. In contrast, deletion of the last eleven amino acids of Gap1p, a region conserved in other amino acid permeases, conferred resistance to NH4+ inactivation. Although the C-terminal region of Gap1p plays an important role in nitrogen control of activity, it was not sufficient to confer this regulation to two NH4(+)-insensitive permeases, namely the arginine (Can1p) and uracil (Fur4p) permeases.
Mol Microbiol 1997 May
PMID:A C-terminal di-leucine motif and nearby sequences are required for NH4(+)-induced inactivation and degradation of the general amino acid permease, Gap1p, of Saccharomyces cerevisiae. 917 53

Mammalian cells coexpress a family of heat shock factors (HSFs) whose activities are regulated by diverse stress conditions to coordinate the inducible expression of heat shock genes. Distinct from HSF1, which is expressed ubiquitously and activated by heat shock and other stresses that result in the appearance of nonnative proteins, the stress signal for HSF2 has not been identified. HSF2 activity has been associated with development and differentiation, and the activation properties of HSF2 have been characterized in hemin-treated human K562 erythroleukemia cells. Here, we demonstrate that a stress signal for HSF2 activation occurs when the ubiquitin-proteasome pathway is inhibited. HSF2 DNA-binding activity is induced upon exposure of mammalian cells to the proteasome inhibitors hemin, MG132, and lactacystin, and in the mouse ts85 cell line, which carries a temperature sensitivity mutation in the ubiquitin-activating enzyme (E1) upon shift to the nonpermissive temperature. HSF2 is labile, and its activation requires both continued protein synthesis and reduced degradation. The downstream effect of HSF2 activation by proteasome inhibitors is the induction of the same set of heat shock genes that are induced during heat shock by HSF1, thus revealing that HSF2 affords the cell with a novel heat shock gene-regulatory mechanism to respond to changes in the protein-degradative machinery.
Mol Cell Biol 1998 Sep
PMID:Heat shock response and protein degradation: regulation of HSF2 by the ubiquitin-proteasome pathway. 971 May 93

The S. cerevisiae SCFCdc4p ubiquitin-protein ligase complex promotes cell cycle transitions through degradation of cell cycle regulators. To investigate SCFCdc4p regulation in vivo, we examined the stability of individual SCFCdc4p components. Whereas Cdc53p and Skp1p were stable, Cdc4p, the F box-containing component responsible for substrate recognition, was short lived and subject to SCF-mediated ubiquitination. Grr1p, another F box component of SCF complexes, was also ubiquitinated. A stable truncated Cdc4pF-beta-gal hybrid protein capable of binding Skp1p and entering into an SCF complex interfered with proteolysis of SCF targets and inhibited cell proliferation. The finding that the F box-containing SCF components are unstable suggests a mechanism of regulating SCF function through ubiquitination and proteolysis of F box components.
Mol Cell 1998 Nov
PMID:Ubiquitination and degradation of the substrate recognition subunits of SCF ubiquitin-protein ligases. 984 30

RSP5, an essential gene of Saccharomyces cerevisiae, encodes a hect domain E3 ubiquitin-protein ligase. Hect E3 proteins have been proposed to consist of two broad functional domains: a conserved catalytic carboxyl-terminal domain of approximately 350 amino acids (the hect domain) and a large, nonconserved amino-terminal domain containing determinants of substrate specificity. We report here the mapping of the minimal region of Rsp5 necessary for its essential in vivo function, the minimal region necessary to stably interact with a substrate of Rsp5 (Rpb1, the large subunit of RNA polymerase II), and the finding that the hect domain, by itself, is sufficient for formation of the ubiquitin-thioester intermediate. Mutations within the hect domain that affect either the ability to form a ubiquitin-thioester or to catalyze substrate ubiquitination abrogate in vivo function, strongly suggesting that the ubiquitin-protein ligase activity of Rsp5 is intrinsically linked to its essential function. The amino-terminal region of Rsp5 contains three WW domains and a C2 calcium-binding domain. Two of the three WW domains are required for the essential in vivo function, while the C2 domain is not, and requirements for Rpb1 binding and ubiquitination lie within the region required for in vivo function. Together, these results support the two-domain model for hect E3 function and indicate that the WW domains play a role in the recognition of at least some of the substrates of Rsp5, including those related to its essential function. In addition, we show that haploid yeast strains bearing complete disruptions of either of two other hect E3 genes of yeast, designated HUL4 (YJR036C) and HUL5 (YGL141W), are viable.
Mol Cell Biol 1999 Jan
PMID:Functional domains of the Rsp5 ubiquitin-protein ligase. 985 58


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