Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The action of the purified thymic factor, thymopoietin, on populations of post-thymic lymphocytes has been studied. Thymopoietin, at concentrations as low as 1.5 ng/ml, uniquely enhanced the proliferative response of peripheral T cells from lymph node and spleen to allogeneic stimulation. Enhancement of the allogeneic response (MLR) was not produced by several polypeptide hormones, including insulin, ACTH, HCG, or Ubiquitin. Treatment of spleen cells with anti-Thy-1 antiserum almost completely abolished the MLR. Thymopoietin's stimulatory effects could not reverse this. Thymopoietin treatment of Thy-1+-enriched spleen cell populations enhanced the MLR even when thymopoietin was removed as early as 2 min after incubation with responding cells. The interaction of thymopoietin with peripheral Thy-1+ cell populations produced a rapid and transient rise in cyclic GMP levels and slightly decreased cyclic AMP levels. These results suggest that thymopoietin interacts with one or more Thy-1+ subpopulations and that this interaction involves early changes in cyclic nucleotide metabolism.
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PMID:Thymopoietin enhances the allogeneic response and cyclic GMP levels of mouse peripheral, thymus-derived lymphocytes. 20 73

The complete amino acid sequence was determined for bovine ubiquitin, and adenylate cyclase stimulating polypeptide, which is probably represented universally in living cells. Ubiquitin has a molecular weight of 8451 and consists of a single polypeptide chain containing 74 amino acid residues. It contains four arginine residues but no cysteine or trytophan residues. The first 61 amino acid residues were obtained by automated Edman degradations. Tryptic digestion of maleated ubiquitin yielded four peptide fragments that were resolved by molecular sieve chromatography and coded in order of decreasing chain length (MT-1, MT-2, MT-3, and MT-4). The automated sequenator determinations on native ubiquintin provided overlapping sequence data for three of these fragments that gave an order of MT-1, MT-3, and then MT-2; Peptide MT-4, a dipeptide, was therefore assigned to the C terminus, and the placement of peptide MT-2 was corroborated by analysis of data from carboxypeptidase digestions of maleated ubiquitin. Peptide MT-2 was domaleated and sequenced by manual Edman degradations through a single lysine residue. It was cleaved at this residue with trypsin, and the two resultant peptides were separated by ion-exchange chromatography. Manual sequencing of the C-terminal demaleated tryptic peptide of MT-2 completed the sequence of MT-2 and that of native ubiquitin. The sequence of ubiquitin was further confirmed and supported by amino acid and parital sequence anlysis of fragments obtained by digestion of maleated ubiquitin with chymotrypsin or staphylococcal protease.
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PMID:The complete amino acid sequence of ubiquitin, an adenylate cyclase stimulating polypeptide probably universal in living cells. 117 Aug 80

Ubiquitin adopts a non-native folded structure in 60% methanol solution at low pH. Two-dimensional nuclear magnetic resonance (2D NMR) was used to measure the hydrogen-exchange rates of backbone amide protons of ubiquitin in both native and methanol forms, and to characterize the structure of ubiquitin in the methanol state. Protection factors (the ratios of experimentally determined exchange rates to the rates calculated for an unfolded polypeptide) for protons in the native form of ubiquitin range from less than 10 to greater than 10(5). Most of the protons that are protected from exchange are located in regions of hydrogen-bonded secondary structure. The most strongly protected backbone amide protons are those of residues comprising the hydrophobic core. Hydrogen exchange from ubiquitin in methanol solution was too rapid to measure directly by 2D NMR, so a labeling scheme was employed, in which exchange with solvent occurred while the protein was in methanol solution. Exchange was quenched by dilution with aqueous buffer after the desired labeling time, and proton occupancies were measured by 1H NMR of the native form of the protein. Protection factors for protons in the methanol form of ubiquitin range from 2.6 to 42, with all protected protons located in hydrogen-bonded structure in the native form. Again, the most strongly protected protons are those of residues in the hydrophobic core. Comparison of the patterns of the hydrogen-exchange rates in the native and methanol forms indicates that almost all of the native secondary structure persists in the methanol form, but that it is almost uniformly destabilized by 4-6 kcal/mol.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Hydrogen exchange in native and alcohol forms of ubiquitin. 133 57

Ubiquitin, an 8.5 kDa polypeptide found almost universally in plants and animals, is a normal component in the lens. The best documented function for ubiquitin involves its conjugation to proteins as a signal to initiate degradation. Conjugates for ubiquitin-dependent degradation tend to be of very high molecular mass and are rapidly degraded. Another role of ubiquitin conjugation may be as a stabilizer during stress for protection of constituent proteins, resulting in ubiquitin conjugates that are long-lived. Examination of clear and cataractous human lenses of < 1 to > 50 years revealed the dramatic accumulation of ubiquitin and ubiquitin conjugates with age, beginning at approximately 10 years. Epithelial tissue contained predominantly conjugates of > 250 kDa, although ubiquitin conjugates were found at 98 and 40-60 kDa in tissues from older donors. The water-soluble, urea-soluble and urea-insoluble fractions of lens cortex and core also contain ubiquitin conjugates that accrue with age. High molecular mass conjugates (> 250 kDa) are particularly prominent in older lens tissue. Cataractous lenses, as compared with normal lenses of the same age, show more of these high molecular mass conjugates in the urea-soluble and urea-insoluble fractions of cortex and core. Heterogeneous conjugates in the 20-85 kDa range accumulate in an age-related fashion in all lens cortex and core fractions. While levels of free ubiquitin are significant in the epithelium and the water-soluble cortex and core for all ages, there is no detectable free ubiquitin in the urea-soluble and urea-insoluble fraction under conditions used in this study.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ubiquitin and ubiquitin conjugates in human lens. 133 33

Ubiquitin, a small 76-amino acid protein which is highly conserved in eukaryotic cells, occurs in several forms other than the free polypeptide. Among these are protein conjugates in which ubiquitin is covalently linked in lysylpeptide bond to lysl residues of other proteins and fusion proteins in which the amino-terminal domain is the precise ubiquitin sequence. Ubiquitin plays a role in cellular proteolytic degradation and in chromatin structure and has been postulated to be involved in the induction of a set of proteins which function during the cellular response to various kinds of environmental stress. We have measured the various forms of ubiquitin in cultures of chicken embryo fibroblasts under normal growth conditions and after treatment with a thermal or chemical stress. Levels of free ubiquitin fell slightly, ubiquitin conjugate levels rose shortly after stress began, and both then increased substantially as one of the cell's ubiquitin-encoding genes was activated by stress. The level of a protein synthesized as the carboxyl-terminal domain of one ubiquitin fusion protein was unchanged by a heat stress. The most dramatic effect was seen in the rapid disappearance of the ubiquitinated form of histone H2A, one of the major ubiquitin conjugates in cells in the interphase portion of their growth cycle. A significant rise in protein turnover was detected as a result of the stress, but occurred only when cells were removed from the stress condition. These results suggest that ubiquitin plays an important role both during and after stress, but fails to support hypotheses for ubiquitin and proteolysis in the activation of stress genes.
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PMID:Ubiquitin in stressed chicken embryo fibroblasts. 282 67

Protein degradation via the nonlysosomal ATP-dependent pathway in rabbit reticulocytes involves a number of components. In the initial event, ubiquitin, an abundant 76-residue polypeptide, becomes covalently linked to the protein substrate in an ATP-requiring reaction. Once marked in this way, the conjugated protein is proteolyzed in a reaction that also requires ATP. Ubiquitin-marking appears to be important to the progression of cells from one stage to another of the cell cycle; it may also be involved in gene activation. Here we show that tRNA is another essential component of the system. Ribonucleases strongly inhibit the ubiquitin- and ATP-dependent degradation of 125I-labeled bovine serum albumin in the reticulocyte system in vitro. RNAs extracted from fractions of the reticulocyte extract or from mouse cells restore proteolytic activity. When the RNA is fractionated by gel electrophoresis, only the tRNA fraction is active in restoring proteolysis. Furthermore, pure mouse tRNAHis, isolated by immunoprecipitation with patient autoimmune sera, restores the proteolytic activity. The possibility that the level of uncharged tRNA in mammalian cells regulates the ubiquitin- and ATP-dependent proteolytic system is discussed.
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PMID:Transfer RNA is an essential component of the ubiquitin- and ATP-dependent proteolytic system. 298 38

The low molecular weight polypeptide required for energy-dependent proteolysis, ubiquitin, is rapidly inactivated by 100,000 X g supernatants of rabbit liver extracts. Ubiquitin inactivation results from limited proteolysis by an endogenous contaminating lysosomal thiol protease having trypsin-like specificity. Evidence for this includes a pH optimum of 5.0 for the first order constant of ubiquitin inactivation and observation that inactivation is inhibited by EDTA, o-phenanthroline, iodoacetamide, p-chloromercuribenzoic acid, phenylmethylsulfonyl fluoride, N alpha-p-tosyl-L-lysine chloromethyl ketone, leupeptin, soybean trypsin inhibitor, and aprotinin. Metals stimulate but are not required for ubiquitin inactivation with the effect apparently mediated by a low molecular weight heat-labile component of crude extracts. When this heat-labile component is removed by gel exclusion chromatography a number of metals inhibit ubiquitin inactivation. In the presence of excess dithiothreitol, inhibition is relatively specific for Zn(II). Inhibition by Zn(II) is specifically overcome competitively by Cd(II) or by a concentration of ubiquitin in excess of Zn(II). The responsible cathepsin possesses a molecular mass of 35 kDa by gel exclusion chromatography and shows marked thermal lability at neutral pH but stability at acid pH. Proteolytic inactivation of ubiquitin results from limited cleavage of the carboxyl-terminal glycine dipeptide required for isopeptide bond formation and is supported by data on isoelectric point changes on subsequent digestion with carboxypeptidase B and by direct amino acid analysis. When the responsible cathepsin is inactivated, liver extracts display ATP,ubiquitin-dependent proteolysis that cannot be ascribed to contaminating erythrocytes. Thus the previous inability to demonstrate energy-dependent proteolysis in liver extracts is accounted for by the artifactual inactivation of ubiquitin.
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PMID:The inactivation of ubiquitin accounts for the inability to demonstrate ATP, ubiquitin-dependent proteolysis in liver extracts. 298 63

Ubiquitin is a highly conserved, 76-amino acid polypeptide recently demonstrated to be involved in ATP-dependent protein degradation in mammalian cells. From immunoblot analyses with anti-human-ubiquitin antibodies we have detected the presence of free ubiquitin in green leaves, etiolated shoots, and dry seeds of the higher plant, oats (Avena sativa L.). We also find that crude oat extracts contain protease(s) that rapidly degrade both oat and human ubiquitin (t1/2 approximately 10 min at 27 degrees C). This proteolysis apparently cleaves ubiquitin at the carboxyl-terminal glycine dipeptide and results in inactivation of the molecule with respect to ligation but does not affect its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Using homogenization conditions that preclude this proteolysis (low pH and the addition of the protease inhibitor p-chloromercuribenzoate) and immunoblotting as an assay for the protein, a procedure for the purification of ubiquitin from etiolated oat shoots was developed. Characterization of purified oat ubiquitin by absorption spectra, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing, radioimmunoassay with anti-human-ubiquitin antibodies, and kinetic analyses using the ubiquitin activating enzyme isolated from rabbit liver indicates that this protein is remarkably similar to the mammalian form. Small differences between the oat and human proteins have been observed by amino acid compositional analyses indicating that the two forms are not totally homologous. Immunoblotting of crude oat extracts has revealed the presence of high molecular weight proteins recognized by anti-ubiquitin antibodies that represent ubiquitin-protein conjugates formed in vivo. Taken together, these data provide evidence that higher plants contain a ubiquitin-dependent proteolytic pathway that is mechanistically identical to that present in animals.
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PMID:Purification and initial characterization of ubiquitin from the higher plant, Avena sativa. 299 56

The lymphocyte cell surface receptor for the high endothelial venules (HEV's) of peripheral lymph nodes is specifically recognized by the monoclonal antibody MEL-14. Three independent complementary DNA (cDNA) clones, each of which encodes the protein ubiquitin, were detected by virtue of the expression of the MEL-14 antigenic determinant on cDNA-beta-galactosidase bacterial fusion proteins. The antigenic determinant defined by MEL-14 resides in the carboxyl terminal 13-amino-acid proteolytic peptide of ubiquitin, but is undetected in intact undenatured ubiquitin and other cellular ubiquitinated proteins. Antisera and monoclonal antibodies to ubiquitin determinants bind to the surface of both HEV-receptor positive and negative cell lines. The MEL-14-identified cDNA clones hydridize to RNA transcripts that encode tandemly repeated ubiquitins. Sequence analysis of these polyubiquitin cDNA's does not identify a leader sequence for export to the cell surface. The expression of the MEL-14 epitope of ubiquitin depends upon its local environment. The steady-state levels of expression of the ubiquitin messenger RNA's do not correlate with either the tissue derivation of the RNA or the expression of the lymphocyte HEV receptor. Regulation of the expression of the HEV receptor is not likely to reflect the transcriptional control of ubiquitin genes, but rather to reflect control of the expression of the HEV core polypeptide or its level or form of ubiquitination.
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PMID:Expression cloning of a lymphocyte homing receptor cDNA: ubiquitin is the reactive species. 300 14

Degradation of intracellular proteins via the ubiquitin- and ATP-dependent proteolytic pathway involves several steps. In the initial event, ubiquitin, an abundant 76-residue polypeptide is covalently linked to the protein substrate in an ATP-requiring reaction. Proteins marked by ubiquitin are selectively proteolyzed in a reaction that also requires ATP. Ubiquitin conjugation to proteins appears also to be involved in regulation of cell cycle and cell division, and probably in the regulation of gene expression at the level of chromatin structure. We have previously shown (Ciechanover, A., Wolin, S. L., Steitz, J. A., and Lodish, H. F. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 1341-1345) that transfer RNA is an essential component of the ubiquitin pathway. Ribonucleases strongly and specifically inhibited the degradation of 125I-labeled bovine serum albumin, while tRNA purified from reticulocyte extract could restore the proteolytic activity. Specifically, pure tRNAHis isolated by immunoprecipitation with human autoimmune serum could restore the proteolytic activity. Here we demonstrate that tRNA is required for conjugation of ubiquitin to some but not all proteolytic substrates of the ubiquitin mediated pathway. Conjugation of 125I-labeled ubiquitin to reduced carboxymethylated bovine serum albumin, alpha-lactalbumin, and soybean trypsin inhibitor was strongly and specifically inhibited by ribonucleases. Consequently, the ATP-dependent degradation of these substrates in the cell-free ubiquitin-dependent reticulocyte system was inhibited as well. Addition of tRNA to the ribonuclease inhibited system (following inhibition of the ribonuclease) restored both the conjugation activity and the ubiquitin- and ATP-dependent degradation of these substrates. Conjugation of ubiquitin to some endogenous reticulocyte proteins was also inhibited by ribonucleases and could be restored by the addition of tRNA. In striking contrast, the conjugation of radiolabeled ubiquitin to lysozyme, oxidized RNase A, alpha-casein, and beta-lactoglobulin was not affected by the ribonuclease treatment, and the degradation of these substrates was significantly accelerated by the ribonucleases. These findings indicate that there are at least two distinct ubiquitin conjugation systems. One requires tRNA, and the other is tRNA independent. These pathways, however, must share some common component(s) of the system, since the inhibition of one system accelerates the other. The possible function of tRNA in the selective conjugation reaction and the possible role of the two distinct ubiquitin marking mechanisms are discussed.
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PMID:Transfer RNA is required for conjugation of ubiquitin to selective substrates of the ubiquitin- and ATP-dependent proteolytic system. 300 81


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