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

Four ubiquitin mRNA size classes were found to be differentially regulated in mesophyll protoplast-derived cultures of Nicotiana sylvestris. Three mRNA families of 1.9, 1.6 and 1.35 kb were expressed as soon as protoplasts were isolated. The 1.9 and 1.6 kb size classes were transiently expressed during the first hours of culture, whereas the level of expression of the 1.35 kb size class was maintained as long as cells kept dividing. A 0.7 kb mRNA size class started to be expressed just before the first divisions were observed. cDNAs corresponding to each of these families were isolated from a 6-h-old protoplast cDNA library and characterized. The 1.9, 1.6 and 1.35 kb mRNAs thus encode 7- or more, 6- and 5-mers, respectively, of ubiquitin whereas the 0.7 kb mRNAs encode a monomer of ubiquitin fused to a carboxyl extension protein of 52 amino acids. The expression of ubiquitin genes was studied, using probes specific for each of these transcript families, during protoplast culture and, for comparison, after various stresses including heat shock, HgCl2 treatment, a viral infection giving rise to a hypersensitive reaction, and an Agrobacterium tumefaciens infection which resulted in tumour formation. The 1.9 and 1.6 kb mRNA size classes were found to be stress-regulated, the 0.7 kb mRNA size class developmentally regulated and the 1.35 kb size class both stress- and developmentally regulated.
Plant Mol Biol 1992 Dec
PMID:Ubiquitin genes are differentially regulated in protoplast-derived cultures of Nicotiana sylvestris and in response to various stresses. 128 39

Two genomic clones (lambda Ubi-1 and lambda Ubi-2) encoding the highly conserved 76 amino acid protein ubiquitin have been isolated from maize. Sequence analysis shows that both genes contain seven contiguous direct repeats of the protein coding region in a polyprotein conformation. The deduced amino acid sequence of all 14 repeats is identical and is the same as for other plant ubiquitins. The use of transcript-specific oligonucleotide probes shows that Ubi-1 and Ubi-2 are expressed constitutively at 25 degrees C but are inducible to higher levels at elevated temperatures in maize seedlings. Both genes contain an intron in the 5' untranslated region which is inefficiently processed following a brief, severe heat shock. The transcription start site of Ubi-1 has been determined and a transcriptional fusion of 0.9 kb of the 5' flanking region and the entire 5' untranslated sequence of Ubi-1 with the coding sequence of the gene encoding the reporter molecule chloramphenicol acetyl transferase (CAT) has been constructed (pUBI-CAT). CAT assays of extracts of protoplasts electroporated with this construct show that the ubiquitin gene fragment confers a high level of CAT expression in maize and other monocot protoplasts but not in protoplasts of the dicot tobacco. Expression from the Ubi-1 promoter of pUBI-CAT yields more than a 10-fold higher level of CAT activity in maize protoplasts than expression from the widely used cauliflower mosaic virus 35S promoter of a 35S-CAT construct. Conversely, in tobacco protoplasts CAT activity from transcription of pUBI-CAT is less than one tenth of the level from p35S-CAT.
Plant Mol Biol 1992 Feb
PMID:Maize polyubiquitin genes: structure, thermal perturbation of expression and transcript splicing, and promoter activity following transfer to protoplasts by electroporation. 131 11

An expression system that utilized yeast copper metallothionein promoter and ubiquitin fusion technology to express the human estrogen receptor gene in yeast is described. We have studied the biochemical and transcriptional regulatory properties of the human estrogen receptor. The biochemical properties of the yeast expressed receptors are identical to the receptors isolated from human tissue. Estradiol mediated activation of transcription by the receptor was studied by a reporter beta-galactosidase gene where expression was under the control of estrogen response elements. Using this expression system and a hyperpermeable yeast strain we have studied the effects of various antiestrogens on the regulation of estrogen receptor function. We demonstrate that tamoxifen and ICI 164,384 are capable of binding to the receptor but neither antiestrogen was able to block the estradiol mediated increase in transcription. In fact, both antiestrogens exerted weak agonist activity in this system.
J Steroid Biochem Mol Biol 1992 Aug
PMID:Human estrogen receptor regulation in a yeast model system and studies on receptor agonists and antagonists. 132 95

The molecular conformation of ubiquitinated structures and the validity of the N-end rule were examined by simulating the molecular mechanics to ascertain the global energy-minimized structure. We examined the chemical linkage involved in attaching the ubiquitin carboxyl terminus to the N-terminus of three different x-hexapeptides, where x is the amino group of the acceptor peptide--either valine, arginine or glutamic acid--(x-K linkage) and to the epsilon-amino group of lysine of the acceptor hexapeptide x-glu1-his2-lys3-gly4-lys5-val6 (K-K linkage) through the formation of an isopeptide bond. Changes in conformation and molecular stability of the multi-ubiquitinated structures were determined by energy-minimization procedures using the SYBYL program developed by Tripos Associates. In the x-K linkage, the ubiquitin molecule is stretched in the beta-pleated sheets and beta-turns while the alpha-helices expand, as the molecule continues to unfold linearly. In the K-K linkage, the ubiquitin molecules have turned into a u-shaped, semi-circular alignment, contracting into a compact, folded structure.
J Mol Graph 1992 Mar
PMID:Molecular conformation of ubiquitinated structures and the implications for regulatory function. 132 99

The stress-induced expression of four different ubiquitin-encoding cDNAs was characterized in potato tuber tissue. The four clones exhibited differences in both structure and expression. The first cDNA encoded a single ubiquitin unit fused to an 80 amino acid ribosomal extension protein identical to the extension protein from tomato. Accumulation of the fusion transcript was induced by injury or ethylene, but not by heat shock. The three remaining ubiquitin cDNAs encoded polyubiquitins with 6 to 7 ubiquitin repeats. The first polyubiquitin gene was induced by injury, heat, or ethylene treatments. The second was induced also by injury or heat, with limited ethylene-dependent accumulation of transcript. Transcript levels of the third polyubiquitin gene were highest in control tubers and decreased markedly with injury, heat shock, or ethylene treatment. The data demonstrate the independent regulation of the different members of the ubiquitin gene family in response to stress and exogenous ethylene.
Plant Mol Biol 1992 Oct
PMID:Expression of stress-responsive ubiquitin genes in potato tubers. 132 70

Ubiquitin is a small, 8 kD protein found in all eukaryotic cells. It is involved in a wide variety of regulatory roles within the cell, including gene expression, ribosome biosynthesis, receptor expression, and the stress response. The best understood of these is that of ubiquitin-mediated proteolysis, in which ubiquitin is covalently attached to specific protein target substrates that are then recognized and degraded by a high molecular weight protease.
Am J Respir Cell Mol Biol 1992 Nov
PMID:Ubiquitin-mediated protein modification and degradation. 132 65

We have characterized a second T. brucei polyubiquitin gene (UbB) that is highly similar in the coding and flanking regions to a previously described T. brucei polyubiquitin gene (UbA). However, UbB differs from UbA in 2 respects: (1) the predicted carboxy-terminal amino acid of UbB is methionine, as opposed to leucine in UbA, and (2) UbB contains approximately 13 ubiquitin repeats, as opposed to approximately 30 repeats in UbA. In Southern blots of intact T. brucei DNA separated by pulsed field gel electrophoresis, the polyubiquitin sequences have been shown to reside on band 19, which may contain 3 chromosomes. Three experiments that target a neomycin-resistance gene to the polyubiquitin locus demonstrate a one-to-one ratio of polyubiquitin 3-flanking sequences, which suggests that UbA and UbB are alleles rather than duplications. Four additional strains of T. brucei and one strain of T. equiperdum show variation in their polyubiquitin gene size, suggesting that this is a common polymorphism.
Mol Biochem Parasitol 1992 Oct
PMID:Allelic polymorphism of the Trypanosoma brucei polyubiquitin gene. 133 86

A lambda gt 11 cDNA library, constructed from poly(A)+ mRNA isolated from Avena fatua aleurone layers incubated with 1 microM gibberellin A1 (GA1) for 4 days, was screened with an anti-idiotypic antiserum raised against the GA-specific monoclonal antibody MAC 182. One positive clone was isolated, sequenced and shown to encode a tetraubiquitin based on the deduced amino acid sequence. This polyubiquitin cDNA exhibited a high degree of homology to a cloned wheat hexaubiquitin in its 3'-non-coding region. Analysis of total RNA isolated from A. fatua aleurone layers, treated without or with a range of concentrations of GA1 from 10(-11) to 10(-6) M, by northern blotting using the cDNA probe revealed 8 different ubiquitin-containing transcript classes all of which are constitutively expressed in aleurone and are regulated by GA1.
Plant Mol Biol 1992 Nov
PMID:cDNA cloning of a tetraubiquitin gene, and expression of ubiquitin-containing transcripts, in aleurone layers of Avena fatua. 133 96

We identified several open reading frames between the regions encoding calmodulin and ubiquitin-EP52/1 in the genome of Trypanosoma brucei. One of these, EFH5, encodes a protein 192 amino acids long. The EFH5 transcript is present in poly(A)+ mRNA and is present at similar levels in the mammalian bloodstream form and the insect procyclic form. EFH5 contains four EF-hand homolog domains, two of which are inferred to bind Ca2+ ions. We expressed EFH5 as a fusion protein in Escherichia coli and demonstrated calcium-binding activity of the fusion protein using the 45Ca-overlay technique. The function of EFH5 remains unknown; however, as the fourth EF-hand homolog identified in trypanosomes, it attests to the broad range of functions assumed by calcium functioning as a second messenger. EFH5, which is most closely related to LAV1-2 from Physarum, represents a distinct subfamily among the EF-hand-containing proteins.
Mol Gen Genet 1992 May
PMID:Identification of a new EF-hand superfamily member from Trypanosoma brucei. 160 64

The mechanism underlying the formation of easily releasable myofilaments, from myofibrils treated with an ATP-containing relaxing solution, was examined in this investigation. The proportion of releasable myofilaments purified from myofibrils of cardiac, fast- and slow-twitch muscles increased as the [ATP] was raised from 0 to 8.5 mM. The protein composition of the easily releasable myofilaments did not differ with increasing ATP concentrations as observed by 5-15% linear gradient SDS-PAGE. There is a nucleotide specificity to the release of myofilaments in the order of ATP greater than GTP much greater than UTP greater than CTP. Experiments with AMP-PNP and inorganic phosphate (Pi) showed that ATP hydrolysis and the build up of Pi are not requirements in the formation of the easily releasable myofilaments. The release of myofilaments was found to be insensitive to variations in pH from 6.5 to 7.5. The ATP stimulation of myofilaments release is ubiquitin-independent, since incubation of purified myofibrils with ubiquitin (1-100 micrograms/ml) at both 20 and 37 degrees C did not change the amount released. Modifying the free sulfhydryl group content by treatment of myofibrils with NEM (0.01-1 mM) or silver nitrate (0.1-10 mM) decreased the proportion of myofilaments that were releasable. Exclusion of 1 mM DTT from the preparation of myofibrils had similar results. These results indicate that the formation of easily releasable myofilaments can be mediated by metabolically related parameters such as the adenosine nucleotides and the reduction-oxidation status of the myofibrillar proteins of striated muscle.
Mol Cell Biochem 1991 May 15
PMID:Regulation of ATP-stimulated releasable myofilaments from cardiac and skeletal muscle myofibrils. 164 79


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