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At least 415 records · Page 23Linked to original sources
PubMed1975

Regulation of RNA polymerase synthesis in Escherichia coli: a mutant unable to synthesize the enzyme at 43 degrees.

We report the isolation of a mutant of E. coli in which the capacity to synthesize RNA polymerase (EC 2.7.7.6) (the beta and beta' subunits) is rapidly lost at 43 degrees. The mutation has no effect on the stability or activity of the polymerase itself. The mutation is recessive and is closely linked to the rif locus (the structural gene for the beta subunit). Using strains carrying the mutation, we have shown that polymerase is present in excess in rapidly growing E. coli cells.

Coliphages↗
PubMed1980

Translation and developmental regulation of RNA encoded by the eukaryotic transposable element copia.

copia-specific RNA was isolated from Drosophila melanogaster tissue culture cells by hybridization of cytoplasmic polyadenylylated RNA to copia DNA immobilized on cellulose. The purified RNA was translated in reticulocyte lysates. One major polypeptide of approximately 51,000 daltons was synthesized in addition to several others between 18,000 and 38,000 daltons. The 51,000-dalton polypeptide and several of the others are encoded by mRNAs of about 2000 nucleotides. The approximate locations on the copia element of the coding sequences for the 51,000-dalton polypeptide and several other proteins were determined by hybrid-arrested translation with copia restriction fragments. The relative abundance of copia-specific RNA was determined at various stages of the Drosophila life cycle. The level of copia-specific RNA is modulated during development of the organism, with the highest level occurring during the larval stages.

Animals↗
PubMed1994

Enhancer 1 binding factor, a Ku-related protein, is a positive regulator of RNA polymerase I transcription initiation.

We have previously characterized a protein, enhancer 1 binding factor (E1BF), from rat cells that can modulate RNA polymerase I-directed transcription of the rat rRNA gene in vitro. E1BF, a heterodimeric DNA binding protein composed of 72-kDa and 85-kDa subunits, is related to the human Ku autoantigen with respect to immunological and certain structural properties. To establish the direct role of E1BF in transcription, we investigated the effect of anti-Ku antibodies on RNA polymerase I-directed transcription in rat and mouse cell extracts. These antibodies, one directed against the 70-kDa Ku subunit and the other against a peptide fragment of this subunit, dissociated the E1BF heterodimer into its two subunits. The DNA-protein complex formed in the presence of the antibodies contained only the 72-kDa subunit. Preincubation of the extracts with these antibodies resulted in an almost complete inhibition of transcription. The reduced transcription was observed when either linear or circular template was used. The inhibitory effect of the antibodies was greatest when added prior to preinitiation complex formation and was minimized significantly when added after establishment of the initiation complex. The repression of rRNA gene transcription was overcome by the addition of purified E1BF. This study demonstrates that E1BF, a Ku-related protein, is required for RNA polymerase I-directed transcription, the 72-kDa subunit is the major DNA binding polypeptide, the factor acts primarily in the formation of the preinitiation complex, and heterodimerization of its two subunits is crucial for maintaining the functional integrity of the protein.

Animals↗
PubMed1999

Cell cycle-dependent regulation of RNA polymerase I transcription: the nucleolar transcription factor UBF is inactive in mitosis and early G1.

Transcription of ribosomal RNA genes by RNA polymerase (pol) I oscillates during the cell cycle, being maximal in S and G2 phase, repressed during mitosis, and gradually recovering during G1 progression. We have shown that transcription initiation factor (TIF)-IB/SL1 is inactivated during mitosis by cdc2/cyclin B-directed phosphorylation of TAFI110. In this study, we have monitored reactivation of transcription after exit from mitosis. We demonstrate that the pol I factor UBF is also inactivated by phosphorylation but recovers with different kinetics than TIF-IB/SL1. Whereas TIF-IB/SL1 activity is rapidly regained on entry into G1, UBF is reactivated later in G1, concomitant with the onset of pol I transcription. Repression of pol I transcription in mitosis and early G1 can be reproduced with either extracts from cells synchronized in M or G1 phase or with purified TIF-IB/SL1 and UBF isolated in the presence of phosphatase inhibitors. The results suggest that two basal transcription factors, e.g., TIF-IB/SL1 and UBF, are inactivated at mitosis and reactivated by dephosphorylation at the exit from mitosis and during G1 progression, respectively.

3T3 Cells↗
PubMed1999

Thioredoxin activation of iron regulatory proteins. Redox regulation of RNA binding after exposure to nitric oxide.

Iron regulatory proteins (IRP1 and IRP2) are redox-sensitive RNA-binding proteins that modulate the expression of several genes encoding key proteins of iron metabolism. IRP1 can also exist as an aconitase containing a [4Fe-4S] cluster bound to three cysteines at the active site. We previously showed that biosynthesis of nitric oxide (NO) induces the transition of IRP1 from aconitase to apoprotein able to bind RNA. This switch is also observed when cytosolic extracts are exposed to NO donors. However, the activation of IRP1 under these conditions is far from maximal. In this study we examined the capacity of physiological reducing systems to cooperate with NO in the activation of IRP1. Cytosolic extracts from the macrophage cell line RAW 264.7 or purified IRP1 were incubated with NO donors and subsequently exposed to glutathione or to thioredoxin (Trx), a strong protein disulfide reductase. Trx was the most effective, inducing a 2-6-fold enhancement of the RNA binding activity of NO-treated IRP1. Furthermore, the effect of NO on IRP1 from cytosolic extracts was abolished in the presence of anti-Trx antibodies. We also studied the combined effect of NO and Trx on IRP2, which exhibits constitutive RNA binding activity. We observed an inhibition of IRP2 activity following exposure to NO donors which was restored by Trx. Collectively, these results point to a crucial role of Trx as a modulator of IRP activity in situations of NO production.

Animals↗
PubMed1990

Transcriptional and Post-Transcriptional Regulation of RNA Levels in Maize Mitochondria.

Relatively little is known about the mechanisms that govern the expression of plant mitochondrial genomes. We have addressed this problem by analyzing the transcriptional activity of different regions of the maize mitochondrial genome using both in vivo and isolated mitochondrial pulse-labeling systems. The regions examined included the protein genes atpA, atp6, and coxII, the 26S, 18S, and 5S rRNA genes, and sequences surrounding the rRNA genes. The rRNAs were found to be transcribed at rates fivefold to 10-fold higher than the protein genes. These rate differences are comparable with the differences in abundance of these species in the total or steady-state RNA population. Pulse-labeled RNA unexpectedly detected transcription of all regions examined, including approximately 21 kilobases of presumed noncoding sequences flanking the rRNA genes for which stable transcripts were not detected. The results obtained with RNA labeled for short pulses in vivo and in isolated mitochondria were similar, suggesting that isolated mitochondria provide a faithful run-on transcription assay. Our results indicate that the absence in total RNA of transcripts homologous to a given region of maize mitochondrial DNA does not necessarily exclude transcriptional activity of that region and that both transcriptional and post-transcriptional processes play important roles in maize mitochondrial genome expression.

Journal Article↗
PubMed1999

Regulation of RNA synthesis by the genomic termini of vesicular stomatitis virus: identification of distinct sequences essential for transcription but not replication.

The RNA-dependent RNA polymerase of vesicular stomatitis virus (VSV), a nonsegmented negative-strand RNA virus, directs two discrete RNA synthetic processes, transcription and replication. Available evidence suggests that the two short extragenic regions at the genomic termini, the 3' leader (Le) and the complement of the 5' trailer (TrC), contain essential signals for these processes. We examined the roles in transcription and replication of sequences in Le and TrC by monitoring the effects of alterations to the termini of subgenomic replicons, or infectious viruses, on these RNA synthetic processes. Distinct elements in Le were found to be required for transcription that were not required for replication. The promoter for mRNA transcription was shown to include specific sequence elements within Le at positions 19 to 29 and 34 to 46, a separate element at nucleotides 47 to 50, the nontranscribed leader-N gene junction. The sequence requirements for transcription within the Le region could not be supplied by sequences found at the equivalent positions in TrC. In contrast, sequences from either Le or TrC functioned well to signal replication, indicating that within the confines of the VSV termini, the sequence requirements for replication were less stringent. Deletions engineered at the termini showed that the terminal 15 nucleotides of either Le or TrC allowed a minimal level of replication. Within these confines, levels of replication were affected by both the extent of complementarity between the genomic termini and the involvement of the template in transcription. In agreement with our previous observations, increasing the extent of complementarity between the natural termini increased levels of replication, and this effect was most operative at the extreme genome ends. In addition, abolishing the use of Le as a promoter for transcription enhanced replication. These analyses (i) identified signals at the termini required for transcription and replication and (ii) showed that Le functions as a less efficient promoter for replication than TrC at least in part because of its essential role in transcription. Consequently, these observations help explain the asymmetry of VSV replication which results in the synthesis of more negative- than positive-sense replication products in infected cells.

Base Sequence↗
PubMed1990

Coordinate post-transcriptional regulation of ferritin and transferrin receptor expression: the role of regulated RNA-protein interaction.

Excess iron results in an increase in the translation of ferritin mRNA and a decrease in the stability of transferrin receptor (TfR) mRNA. These coordinate regulatory events are mediated by similar sequence/structure motifs that exist within the 5' untranslated region (5'UTR) of the ferritin mRNA and the 3'UTR of the TfR mRNA. We have referred to these motifs as iron-responsive elements (IREs). The IREs from both transcripts interact with a cytoplasmic protein that we have called the IRE-binding protein (IRE-BP). The activity but not the amount of the IRE-BP is dependent on the cellular iron status. The biochemical basis for the altered activity of the IRE-BP appears to be the reversible oxidation-reduction of one or more cysteines in the IRE-BP. The IRE-BP is a 90- to 95-kD cytosolic protein that has been purified to homogeneity by RNA affinity chromatography, and the cDNA corresponding to the IRE-BP has been molecularly cloned. Collectively, our data support a model in which the interaction between the IRE-BP and the ferritin IRE results in attenuation of translation, and similar interaction with TfR mRNA can protect the transcript from rapid degradation mediated by a rapid turnover determinant within the 3'UTR.

Base Sequence↗
PubMed1979

Regulation of RNA synthesis in Tetrahymena pyriformis: secretion of regulatory factors.

The rate of ribosomal RNA synthesis varies greatly with the population density in both exponentially and synchronously growing populations of Tetrahymena pyriformis. Shortly after inoculation of the population - at relatively low cell densities - a gene-dose effect dominates the picture, and a doubling in the gene number is immediately followed by a doubling in the rate of RNA synthesis. However, also other mechanisms are controlling the rate of RNA synthesis. Generally one finds high rates of RNA synthesis in the lag phase of newly inoculated cells, decreasing rate of RNA synthesis during most of the exponential growth phase and very low rate of synthesis in stationary phase cells. We now have results which show that the repression of RNA synthesis in densely populated cultures is caused by a dialysable factor, which is secreted by the cells. If cells are inoculated on a medium which contains this factor the high initial rate of RNA synthesis normally observed is prevented, but the cells multiply and grow with normal generation time until normal stationary-phase population densities are reached.

Animals↗
PubMed1980

On the role of small peptides in the regulation of RNA synthesis in Tetrahymena pyriformis.

Tetrahymena cells secrete a factor which inhibits RNA synthesis in vivo and in vitro. The factor is a relatively small peptide with a molecular weight between 300 and 1500 Daltons. Other, non-specific peptides in the broth medium or added to a chemically defined medium have a stimulatory effect on RNA synthesis in vivo and such peptides also stimulate the in vitro synthesis of RNA in a r-chromatin preparation. On the basis of these results we conclude that such extracellular small peptides compete with a specific factor which is part of the intracellular regulatory mechanism controlling the rate of RNA synthesis. The consequence of such competition is a high overproduction of ribosomal RNA in cells inoculated on peptide-rich broth media.

Animals↗