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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The macronuclear DNAs from 20 different species of Tetrahymena were characterized using Alternating Orthogonal Field (AOF) gel electrophoresis. Each species has approximately 300 different macronuclear DNA molecules that range in size from about 100-2000 kb pairs. Although the individual macronuclear DNA molecules are not well resolved on an AOF gel, most species have a unique profile of macronuclear DNA. The sequences that hybridize with histone H4 (Tetrahymena) and ubiquitin (yeast) genes were identified on the separated macronuclear DNA molecules of the different species. All species have 2 histone H4 genes located on macronuclear DNA molecules of different sizes. This is consistent with the duplication of the histone H4 gene prior to the speciation events leading to the various species of Tetrahymena. The number and sizes of the macronuclear DNA molecules that hybridize with the ubiquitin probe vary from species to species. A grouping of the different species of Tetrahymena based on this hybridization pattern parallels groupings of the species based on ribosomal RNA sequences and isoenzymes. Some intraspecific variation among different strains of Tetrahymena thermophila was detected using ubiquitin and 5S ribosomal RNA as probes.
J Mol Evol 1986
PMID:Characterization of the macronuclear DNA of different species of Tetrahymena. 303 19

The crystal structure of human ubiquitin has been solved by x-ray diffraction methods and refined by standard procedures to a conventional crystallographic R factor of 0.176 at 1.8-A resolution (Vijay-Kumar, S., Bugg, C.E., and Cook, W.J. (1987) J. Mol. Biol. 194, 525-538). Crystals of yeast and oat ubiquitin have been grown using human ubiquitin crystals as seeds. Diffraction data for yeast and oat ubiquitin have been collected to a resolution of 1.9 and 1.8 A, respectively. Difference Fourier electron-density maps reveal that the structures of yeast and oat ubiquitin are quite similar to human ubiquitin. All the amino acid changes are clustered in two small patches on one surface of the molecule. This surface is probably not involved in conjugation with proteins destined for ATP-dependent proteolysis.
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PMID:Comparison of the three-dimensional structures of human, yeast, and oat ubiquitin. 303 65

A previously isolated cDNA clone, pLK229, that is specific for mRNA developmentally expressed during Dictyostelium discoideum spore germination and multicellular development, was used to screen two genomic libraries. Two genomic sequences homologous to pLK229 were isolated and sequenced. Genomic clone p229 is identical to the cDNA clone pLK229 and codes for a polypeptide of 381 amino acids. This polypeptide is composed of five tandem repeats of the same 76-amino-acid sequence. Clone lambda 229 codes for a protein of 229 amino acids, containing three tandem repeats of the identical 76-amino-acid sequence. A computer search for homology to known proteins revealed that the 76-amino-acid repeat was identical to human and bovine ubiquitin except for two amino acid differences.
Mol Cell Biol 1987 Jun
PMID:Structure of two developmentally regulated Dictyostelium discoideum ubiquitin genes. 303 45

The crystal structure of human erythrocytic ubiquitin has been refined at 1.8 A resolution using a restrained least-squares procedure. The crystallographic R-factor for the final model is 0.176. Bond lengths and bond angles in the molecule have root-mean-square deviations from ideal values of 0.016 A and 1.5 degrees, respectively. A total of 58 water molecules per molecule of ubiquitin are included in the final model. The last four residues in the molecule appear to have partial occupancy or large thermal motion. The overall structure of ubiquitin is extremely compact and tightly hydrogen-bonded; approximately 87% of the polypeptide chain is involved in hydrogen-bonded secondary structure. Prominent secondary structural features include three and one-half turns of alpha-helix, a short piece of 3(10)-helix, a mixed beta-sheet that contains five strands, and seven reverse turns. There is a marked hydrophobic core formed between the beta-sheet and alpha-helix. The molecule features a number of unusual secondary structural features, including a parallel G1 beta-bulge, two reverse Asx turns, and a symmetrical hydrogen-bonding region that involves the two helices and two of the reverse turns.
J Mol Biol 1987 Apr 05
PMID:Structure of ubiquitin refined at 1.8 A resolution. 304 Oct 7

Ubiquitin is remarkable for its ubiquitous distribution and its extreme protein sequence conservation. Ubiquitin genes comprise direct repeats of the ubiquitin coding unit with no spacers. The nucleotide sequences of several ubiquitin repeats from each of humans, chicken, Xenopus, Drosophila, barley, and yeast have recently been determined. By analysis of these data we show that ubiquitin is evolving more slowly than any other known protein, and that this (together with its gene organization) contributes to an ideal situation for the occurrence of concerted evolution of tandem repeats. By contrast, there is little evidence of between-cluster concerted evolution. We deduce that in ubiquitin genes, concerted evolution involves both unequal crossover and gene conversion, and that the average time since two repeated units within the polyubiquitin locus most recently shared a common ancestor is approximately 38 million years (Myr) in mammals, but perhaps only 11 Myr in Drosophila. The extreme conservatism of ubiquitin evolution also allows the inference that certain synonymous serine codons differing at the first two positions were probably mutated at single steps.
J Mol Evol 1987
PMID:Ubiquitin genes as a paradigm of concerted evolution of tandem repeats. 304 Oct 10

The proteins encoded by both viral and cellular forms of the c-myc oncogene have been previously demonstrated to have exceptionally short in vivo half-lives. In this paper we report a comparative study on the parameters affecting turnover of nuclear oncoproteins c-myc, c-myb, and the rapidly metabolized cytoplasmic enzyme ornithine decarboxylase. The degradation of all three proteins required metabolic energy, did not result in production of cleavage intermediates, and did not involve lysosomes or ubiquitin. A five- to eightfold increase in the half-life of c-myc proteins, and a twofold increase in the half-life of c-myb proteins was detected after heat-shock treatment at 46 degrees C. In contrast, heat shock had no effect on the turnover of ornithine decarboxylase. Heat shock also had the effect of increasing the rate of c-myc protein synthesis twofold, whereas c-myb protein synthesis was decreased nearly fourfold. The increased stability and synthesis of c-myc proteins led to an overall increase in the total level of c-myc proteins in response to heat-shock treatment. Furthermore, treatments which reduced c-myc and c-myb protein turnover, such as heat shock and exposure to inhibitors of metabolic energy production, resulted in reduced detergent solubility of both proteins. The recovery from heat shock, as measured by increased turnover and solubility, was energy dependent and considerably more rapid in thermotolerant cells.
Mol Cell Biol 1988 Jun
PMID:c-myc and c-myb protein degradation: effect of metabolic inhibitors and heat shock. 304 80

The data available at present indicates there are three distinct functions of ubiquitin, two of which are related to protein conjugation. The first of these has been extensively studied by our laboratory and others interested in nucleosomes and changes in chromatin states. The ubiquitin-histone (Ub-2A, Ub-2B) conjugation reaction now appears to be a very dynamic process. In the deconjugation (lyase) reaction, both the histone 2A and the ubiquitin are left intact and in a form which makes possible ready reconjugation. Accordingly, this may be a mechanism for "moment-to-moment" Control of the genome. The second function in which ubiquitin is conjugated involves proteolytic activity. This activity is correlated with protein turnover. In this process, the ubiquitin-protein conjugate apparently serves as a "signal" for the protease cleavage of the protein. The released ubiquitin is also intact and is probably available for reconjugation. In the third function, ubiquitin was suggested to serve as a "hormone". The studies thus far have been carried out primarily on induction of T- and B-lymphocytes, reduction or delay of Coombs' positivity and reduction of spleen weight. The precise physiological role of this reported function is still unclear, particularly because the ubiquitin used was probably not the physiologically active form.
Mol Cell Biochem 1981 Nov 13
PMID:Ubiquitin - protein conjugates. 627 56

Rabbit hexokinase (EC 2.7.1.1) has been shown to exist in reticulocytes as two distinct molecular forms, designated hexokinase Ia and Ib, but only one of these was consistently present in mature red cells. In vivo, hexokinase Ia and Ib show a decay rate of 3 and 8% a day, respectively, while in vitro they show a similar stability. The possibility that the proteolytic activities of the reticulocyte could be responsible for the fast decay of hexokinase was investigated. No differences were found in the decay rates of hexokinase Ia and Ib during in vitro reticulocyte maturation in presence or absence of proteolytic inhibitors. Contrariwise, many findings indicate the ATP-dependent proteolytic system of the reticulocyte as a possible mechanism. In fact, the decay of hexokinase and the degradation of 3H-globins are both stimulated by ATP and ubiquitin; they show similar kinetic properties and both disappear during reticulocyte maturation. The cellular localization of hexokinase Ia and Ib was shown to be responsible for the differences found between their decay rates.
Mol Cell Biochem 1984
PMID:Rabbit red blood cell hexokinase. Evidences for an ATP-dependent decay during cell maturation. 636 15

Ubiquitin is a 76-amino-acid protein with a remarkably high degree of conservation between all known sequences. Ubiquitin genes are almost always multicopy in eukaryotes, and often are found as polyubiquitin genes--fused tandem repeats which are coexpressed. Seventeen ubiquitin sequences from the amitochondrial protist Trichomonas vaginalis have been examined here, including an 11-repeat fragment of a polyubiquitin gene. These sequences reveal a number of interesting features that are not seen in other eukaryotes. The predicted amino acid sequences lack several universally conserved residues, and individual units do not always encode identical peptides as is usually the case. On the nucleotide level, these repeats are in general highly variable, but one region in the polyubiquitin is extremely homogeneous, with seven repeats absolutely identical. Such extended stretches of homogeneity have never been observed in ubiquitin genes and since substitutions are common in other coding units, it is likely that these repeats are the product of a very recent homogenization or amplification.
J Mol Evol 1995 Nov
PMID:Concerted evolution in protists: recent homogenization of a polyubiquitin gene in Trichomonas vaginalis. 749 Jul 69

Ubiquitin gene expression and the ubiquitination of proteins in the posterior silk glands (PSG) of B. mori were analyzed developmentally with respect to fibroin synthesis and degeneration. Two ubiquitin transcripts are expressed throughout larval stages, and the level of each transcript is regulated differently. The larger transcript, a polyubiquitin mRNA, was abundant during the molt stage, while levels of the smaller ubiquitin transcript increased immediately after molting. Only a single 65 kDa ubiquitinated protein was detected late in the 5th instar, and the amount increased up to spinning stage. This ubiquitinated protein may participate in the PSG degeneration.
Insect Biochem Mol Biol 1994 Jul
PMID:Protein ubiquitination in the posterior silk glands of Bombyx mori. 752 Aug 1


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