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Query: UNIPROT:P06889 (Mol)
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To test features of the current model of transcription attenuation in amino acid biosynthetic operons, alterations were introduced into the trp operon leader region and expression of the mutated operons was examined in miaA and miaA+ Escherichia coli strains that lacked the trp repressor. The miaA mutation prevents modification of the adenosine residue immediately 3' of the anticodon of tRNAs that interact with codons beginning with uridine. The undermodified tRNA(Trp) in miaA strains is thought to increase readthrough at the trp attenuator by slowing ribosome movement over two tandem Trp codons in the 14-codon leader peptide coding region. The rate of translation of these two "control codons" is thought to be the key step in determining the extent of transcription attenuation in the trp leader region. Sequential deletion of trpL DNA specifying the leader peptide initiation region, RNA segment 1, RNA segment 2 and RNA segment 3 alternately decreased and increased trp operon expression, a result consistent with previous findings in another bacterium and the generally accepted model for transcription attenuation. Replacement of the tandem Trp control codons by AGG-UGC (Arg-Cys) codons eliminated the miaA-dependent increase in transcription readthrough. Replacement of the Trp control codons by AGG-UGA (Arg-stop) codons caused complete readthrough at the trp attenuator as well as abolishing the miaA effect. Presumably, the ribosome terminating translation at the new UGA codon mimics the effect of a stalled ribosome at the Trp control codons. This finding suggests that ribosome dissociation at some stop codons is slow relative to the time required for transcription of the trp leader region. Thus, most ribosomes translating the trp leader peptide coding region may remain attached to the natural UGA stop codon until after the attenuation decision is made. The interpretation supports models for trp operon attenuation in which the elevated basal level readthrough is determined by occasional ribosome release prior to synthesis of the 3:4 terminator hairpin.
J Mol Biol 1990 Nov 05
PMID:Replacement of the Escherichia coli trp operon attenuation control codons alters operon expression. 223 31

Progestin antagonism of estrogen action is thought to be due, at least in part, to progestin down-regulation of the estrogen receptor (ER). The molecular mechanisms subserving this effect, and the functional consequences in terms of target cell sensitivity to estrogens, are poorly understood. The present study was undertaken to address these issues with particular emphasis on progestin regulation of ER gene expression at the mRNA level. The T-47D human breast cancer cell line was treated with the synthetic progestin, ORG 2058, and the resultant changes in ER mRNA and ER levels determined by Northern analysis and radioligand binding, respectively. Treatment of T-47D cells with ORG 2058 resulted in rapid down-regulation of ER mRNA levels to a nadir of 35-40% of control by 6 h. This fall in ER mRNA levels was accompanied by a slower but more sustained fall in ER binding to a nadir of 20% of control at 24 h. Between 12 and 24 h ER mRNA levels recovered partially while ER ligand binding continued to fall. At 48 h both ER mRNA and ER concentrations remained depressed, although the latter to a greater extent. ER mRNA half-life was determined by [3H]uridine incorporation to be approximately 60 min and was unaffected by progestin treatment during the early rapid phase of ER mRNA down-regulation. These data demonstrate that progestins cause rapid down-regulation of the ER mRNA and suggest that during the early rapid phase of this effect, reduced transcription of the ER gene rather than altered ER mRNA half-life mediate this effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1990 Jun
PMID:Progestin regulation of estrogen receptor messenger RNA in human breast cancer cells. 223 41

1. Rats which survived hypoglycemia by insulin, hypoxia by 10% O2, or ischemia by carotid ligation and hypotension to 40 mm Hg, evidenced no changes in cerebrospinal fluid (CSF) uridine. Animals which died soon after the above interventions or as a result of KCl-induced cardiac arrest had elevated CSF uridine concentrations. 2. Injection of whole blood or the soluble contents of lysed blood cells into the lateral ventricle of rats reduced CSF uridine to less than one-half normal at 24 hrs but values returned to normal 3 days later. Changes in hypoxanthine resembled those of uridine, but were less dramatic, whereas xanthine concentrations were largely unaltered. Intraventricular injection of plasma or saline did not alter CSF uridine. 3. It seems most likely that low CSF uridine concentrations previously reported in head injury patients may be secondary to the effects of blood cell contents in the cerebrospinal fluid, rather than responses to altered metabolism in neurons or glia cells.
Cell Mol Neurobiol 1990 Sep
PMID:Opposite alterations in cerebrospinal fluid uridine after severe cerebral ischemia or intrathecal blood injection. 225 61

Diffracting crystals, suitable for X-ray crystallographic analysis, have been obtained from large (50 S) ribosomal subunits from Thermus thermophilus. These crystals, with P4(1)2(1)2 symmetry and a unit cell of 495 A x 495 A x 196 A, reach typically a size of 0.15 mm x 0.25 mm x 0.35 mm. Using synchrotron radiation at cryo-temperature, these crystals diffract X-rays to better than 9 A resolution, and do not show any measurable decay after a few days of irradiation. They complete a series of crystals, grown by us, from ribosomal particles of the same source, including a 30 S subunits, 70 S ribosomes and complexes of the latter with: (1) an oligomer of 35 uridine residues and (2) the same oligonucleotide together with approximately two Phe-tRNA(Phe) molecules. Crystallographic analysis of the various members of this series should provide information for investigating the conformational changes that take place upon the association of ribosomes from their subunits as well as upon binding of non-ribosomal components that participate in protein biosynthesis.
J Mol Biol 1990 Nov 20
PMID:Characterization and preliminary crystallographic studies on large ribosomal subunits from Thermus thermophilus. 225 27

Transcripts from the rps13 locus, which encodes ribosomal protein S13, in Oenothera and Daucus mitochondria are edited by several cytidine to uridine transitions in both plants. Analysis of individual cDNA clones and polymerase chain reaction (PCR)-amplified cDNA from the total mitochondrial mRNA population shows different editing patterns in the two species. Although the same genomic triplet is conserved, nucleotides altered in the mRNA of one species are not necessarily edited in the other. Individual editing sites appear to be modified to varying degrees in the mRNA populations in both plant species, indicating that completely edited transcripts constitute only a minor fraction of the rps13 mRNA molecules.
Mol Gen Genet 1990 Dec
PMID:Species-specific RNA editing patterns in the mitochondrial rps13 transcripts of Oenothera and Daucus. 226 44

Polyadenylated transcripts homologous to highly repetitive DNA were found in root tips of Vicia faba by Northern blot hybridization. Electron microscope autoradiography using [3H]uridine as a probe revealed transcription of condensed chromatin in various higher plants. This is consistent with the general rule that highly repetitive DNA is located within condensed chromatin, but it is new that this chromatin fraction is active in RNA synthesis to a considerable amount. Semi-quantitative comparison of the intensity of transcription in species with widely differing 2C DNA contents by means of light microscope autoradiography revealed an inverse relationship between the amount of 2C DNA (and condensed chromatin), and the rate of RNA synthesis.
Mol Biol Rep 1985 Apr
PMID:Transcription of repetitive DNA in condensed plant chromatin. 241 3

In this study, the effects of 15 days of estradiol (E2) on tritiated-uridine incorporation were autoradiographically examined, on a cell-by-cell basis, in 4 E2-concentrating regions of the female rat brain. These areas included the ventromedial hypothalamus and medial amygdala nucleus, 2 regions involved in the behavioral components of reproduction, and the medial preoptic area and arcuate nucleus of the hypothalamus, 2 regions involved in the endocrine components of reproduction. Chronic E2 caused a 50% and 52% increase in tritiated-uridine incorporation in the arcuate nucleus and medial preoptic area, but was without effect in the ventromedial hypothalamus and medial amygdala nucleus. Somal area was also increased with E2 in the arcuate nucleus and medial preoptic area (16% and 43%, respectively) but not in the ventromedial hypothalamus and medial amygdala nucleus. The results indicate that the effects of estradiol on levels of newly synthesized RNA vary in a functionally and regionally specific manner within the brain.
Mol Cell Endocrinol 1986 Apr
PMID:Regional specificity in estradiol effects on [3H]uridine incorporation in rat brain. 242 68

Picornavirus infection induces a profound inhibition of labelling of newly synthesized RNA in some cell lines. EMC virus blocks transcription in L929 cells, particularly at early times during infection. This inhibition is not dependent on virus gene expression, since it occurs with UV-inactivated virus and also in the presence of translation inhibitors. The inhibition can be largely accounted for by the blockade of [3H]nucleoside transport, as suggested by the transport kinetics and incorporation of labelled nucleoside from preloaded cells. The inhibition of transport and incorporation into TCA-precipitable material was observed with pyrimidine (uridine, thymidine and cytosine) and purine nucleosides (adenosine and guanosine), but the blockade by EMC virus was higher with the latter nucleosides. Preloading of cells with any of these nucleosides resulted in a decreased effect on nucleoside incorporation into nucleic acid after virus infection. These results suggest that the inhibition of incorporation of labelled nucleosides into nucleic acid in EMC virus-infected cells can be explained, at least in part, by the decreased pool size of the phosphorylated nucleosides. These effects are not specific for L cells, because they are also observed in other cell lines.
Mol Cell Biochem 1986 Jun
PMID:The inhibition of nucleic acid synthesis in encephalomyocarditis virus-infected L929 cells: effects on nucleoside transport. 242 45

The nucleocytoplasmic RNA transport in rat ventral prostate was studied by electron microscope autoradiography. Isolated prostate acini from normal, castrated, and DHT-treated animals were labeled in vitro with [3H]uridine for 5 min and chased for 0, 15, 30 min and 4 hr. The results show that DHT induces a significant nucleolar enlargement but intranuclear migration of rRNA is not apparently affected by androgens; migration of RNA through euchromatin is delayed by castration and stimulated by DHT; migration through the nuclear envelope is androgen-dependent. In addition prostate acini were maintained for 24 hr in suspension culture in order to study the in vitro effects of DHT. The result show that DHT stimulates uridine uptake and/or incorporation but induces no nucleolar enlargement; DHT has no clear effects on RNA migration kinetics; cytoplasmic transport of RNA in cells cultured in medium with or without DHT is severely impaired but is restored after supplementation of medium with insulin and dexamethasone.
J Ultrastruct Mol Struct Res 1986 Jan
PMID:Quantitative ultrastructural autoradiographic study of RNA transport in rat ventral prostate. 243 32

4.5S RNA is a group of RNAs 90 to 94 nucleotides long (length polymorphism due to a varying number of UMP residues at the 3' end) that form hydrogen bonds with poly(A)-terminated RNAs isolated from mouse, hamster, or rat cells (W. R. Jelinek and L. Leinwand, Cell 15:205-214, 1978; F. Harada, N. Kato, and H.-O. Hoshino, Nucleic Acids Res. 7:909-917, 1979). We have cloned a gene that encodes the 4.5S RNA. It is repeated 850 (sigma = 54) times per haploid mouse genome and 690 (sigma = 59) times per haploid rat genome. Most, if not all, of the repeats in both species are arrayed in tandem. The repeat unit is 4,245 base pairs long in mouse DNA (the complete base sequence of one repeat unit is presented) and approximately 5,300 base pairs in rat DNA. This accounts for approximately 3 X 10(6) base pairs of genomic DNA in each species, or 0.1% of the genome. Cultured murine erythroleukemia cells contain 13,000 molecules per cell of the 4.5S RNA, which can be labeled to equilibrium in 90 min by [3H]uridine added to the culture medium. The 4.5S RNA, therefore, has a short half-life. The 4.5S RNA can be cross-linked in vivo by 4'-aminomethyl-4,5',8-trimethylpsoralen to murine erythroleukemia cell poly(A)-terminated cytoplasmic RNA contained in ribonucleoprotein particles.
Mol Cell Biol 1986 May
PMID:4.5S RNA is encoded by hundreds of tandemly linked genes, has a short half-life, and is hydrogen bonded in vivo to poly(A)-terminated RNAs in the cytoplasm of cultured mouse cells. 243 Dec 80


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