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At least 361 records · Page 20Linked to original sources
PubMed2003

Arabidopsis transportin1 is the nuclear import receptor for the circadian clock-regulated RNA-binding protein AtGRP7.

We characterized the Arabidopsis orthologue of the human nuclear import receptor transportin1 (TRN1). Like the human receptor, Arabidopsis TRN1 recognizes nuclear import signals on proteins that are different from the classical basic nuclear localization signals. The M9 domain of human heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is the prototype of such signals. We show that AtTRN1 binds to similar domains in hnRNP-like proteins from plants. AtTRN1 also interacts with human hnRNP A1 and with yeast Nab2p, two classical import cargo proteins of transportin in these organisms. Like all nuclear transport receptors of the importin-beta family, AtTRN1 binds to the regulatory GTPase Ran from Arabidopsis. We demonstrated that the amino terminus of AtTRN1 is necessary for this interaction. Recombinant AtTRN1 conferred nuclear import of fluorescently labelled BSA-M9 peptide conjugates in permeabilized HeLa cells, functionally replacing human TRN1 in these in vitro nuclear import assays. We identified three plant substrate proteins that interact with AtTRN1 and contain M9-like domains: a novel Arabidopsis hnRNP that shows high similarity to human hnRNP A1 and two small RNA-binding proteins from Arabidopsis, AtGRP7 and AtGRP8. Nuclear import activity of the M9-like domains of these plant proteins was demonstrated in vivo by their ability to confer partial nuclear re-localisation of a GFP fusion protein containing a nuclear export signal. In addition, fluorescently labelled AtGRP7 was specifically imported into nuclei of permeabilized HeLa cells by Arabidopsis AtTRN1 and human TRN1. These results suggest that the transportin-mediated nuclear import pathway is highly conserved between man, yeast and plants.

Amino Acid Sequence↗
PubMed2006

Regulation of RNA polymerase III transcription during hypertrophic growth.

The cell division-independent growth of terminally differentiated cardiomyocytes is commonly associated with cardiovascular disease. We demonstrate that it is accompanied by a substantial rise in transcription by RNA polymerase (pol) III, which produces essential components of the biosynthetic apparatus, including 5S rRNA and tRNAs. This increase in transcription is achieved by changes in both the activity and level of the essential pol III-specific transcription factor TFIIIB. Erk and c-Myc, which directly activate TFIIIB in proliferating fibroblasts, also induce pol III transcription in growing cardiomyocytes. Furthermore, hypertrophic stimulation increases expression of the essential TFIIIB subunit Brf1, an effect not seen when fibroblasts proliferate. Erk mediates this induction of Brf1 expression and therefore contributes in at least two ways to pol III transcriptional activation during hypertrophy. Increased production of tRNA and 5S rRNA will contribute to the enhanced translational capacity required to sustain hypertrophic growth.

Animals↗
PubMed1988

A nerve growth factor-regulated messenger RNA encodes a new intermediate filament protein.

Differential screening of a cDNA library from the PC12 rat pheochromocytoma cell line previously revealed a clone, clone 73, whose corresponding mRNA is induced by nerve growth factor (NGF). Induction parallels NGF-stimulated PC12 differentiation from a chromaffinlike phenotype to a sympathetic neuronlike phenotype. We report that DNA sequence analysis reveals that clone 73 mRNA encodes an intermediate filament (IF) protein whose predicted amino acid sequence is distinct from the known sequences of other members of the IF protein family. The sequence has highest homology with desmin and vimentin and includes the highly conserved central alpha-helical rod domain with the characteristic heptad repeat of hydrophobic residues, but has lower homology in the amino-terminal head and carboxyl-terminal tail domains. The head domain contains a large number of serine residues which are potential phosphorylation sites. The expression of clone 73 in vivo in the nervous system of the adult rat was investigated by in situ hybridization of clone 73 probes to tissue sections. The mRNA is expressed at high levels in ganglia of the peripheral nervous system, including the superior cervical ganglion (sympathetic), ciliary ganglion (parasympathetic), and dorsal root ganglion (sensory). In the central nervous system, motor nuclei of cranial nerves III, IV, V, VI, VII, X, and XII as well as ventral horn motor neurons and a restricted set of other central nervous system nuclei express the clone 73 mRNA. Tissues apart from those of the nervous system did not in general express the mRNA, with only very low levels detected in adrenal gland. We discuss the implications of these results for the mechanism of NGF-induced PC12 cell differentiation, the pathways of neuronal development in vivo, and the possible function of the clone 73 IF protein and its relationship to other IF proteins.

Amino Acid Sequence↗
PubMed2005

Two novel proteins, dos1 and dos2, interact with rik1 to regulate heterochromatic RNA interference and histone modification.

BACKGROUND: Chromosomal behavior during mitosis and meiosis depends in part on heterochromatic modifications such as histone H3 lysine-9 methylation (H3K9me). In fission yeast, the Heterochromatin Protein 1 homolog Swi6 recognizes H3K9me, silences transcription, and retains cohesin at pericentromeric repeats. Heterochromatin formation also depends on processing of transcripts derived from centromeric repeats by the RNAi machinery. The DDB1 homolog, Rik1, and histone methyltransferase, Clr4, act in a complex to promote H3K9me. However, the mechanism underlying this interaction is poorly understood. RESULTS: Using a cytological screen, we have identified two novel genes, dos1(+) and dos2(+), which are required for localization of Swi6. Deletion of either of these genes results in mitotic and meiotic chromosome missegregation, defects in mitotic centromeric cohesion and meiotic telomere clustering, and loss of heterochromatic silencing. Dos1 is predominantly located in the nucleus in a Dos2-dependent manner and directly interacts with Rik1. Each of these genes is required for the association of H3K9me with centromeric repeats, as well as for the production of small interfering RNAs. CONCLUSIONS: Dos1 and Dos2 are required for the formation of heterochromatin in fission yeast. We hypothesize that the physical interaction between Dos1 and Rik1 represents a role in regulating activity of the Rik1/Clr4 complex. Dos2 contributes to this role by regulating Dos1 localization. Our findings suggest a mechanism for recruitment of Clr4 in the RNAi-dependent heterochromatin pathway, in which Dos1 and Dos2 are essential.

Carrier Proteins↗
PubMed1991

Arginine/serine-rich domains of the su(wa) and tra RNA processing regulators target proteins to a subnuclear compartment implicated in splicing.

Two unrelated pre-mRNA splicing regulators-suppressor-of-white-apricot (su(wa)) and transformer (tra)-contain distinctive, approximately 120 amino acid arginine/serine (RS)-rich domains. Deletion of the su(wa) RS domain eliminates function. Replacement with the tra RS domain restores su(wa) function to nearly wild-type levels. Replacement with a 10 amino acid simple nuclear entry signal allows partial, inefficient function. Thus, the su(wa) RS domain apparently serves a generic function(s) subsuming nuclear entry. Moreover, immunocytochemical studies demonstrate that both RS domains specifically direct localization of a fused reporter protein to a punctate subnuclear compartment shown previously to be enriched in several constitutive splicing components. We propose that RS domains are a new class of targeting signals directing concentration of proteins in a subnuclear compartment implicated in splicing metabolism.

Amino Acid Sequence↗
PubMed1974

Ribonucleic acid regulation in amino acid-limited cultures of Escherichia coli grown in a chemostat.

The regulation of ribonucleic acid (RNA) synthesis was examined in cultures of bacteria whose growth was limited in the chemostat by the supply of a required amino acid. Strains possessing the relaxed (relA) mutation accumulated excess RNA (relative to protein) at low growth rates when growth was limited by arginine, histidine, or cysteine but not when limited by methionine. In contrast, stringent (relA(+)) strains maintained a constant RNA/protein ratio with decreasing growth rate regardless of the amino acid used to limit growth. The presence of excess RNA in relaxed strains was accompanied by an absence of increase in RNA production upon addition of chloramphenicol, a lag upon shift-up in growth by addition of excess of the limiting amino acid, and a decreased rate of production of beta-galactosidase upon induction. Analysis of the RNA accumulated in relaxed strains indicated it was present as transfer RNA as well as 50S and 30S ribosomal subunits. Microscope examination of the relaxed strains during histidine-, arginine-, or cysteine-limited growth in the chemostat showed them to be 10 to 20 times longer in size than the stringent strains. Also, cell density was reduced to one-tenth when the increased size was observed. An analysis of the amount of ppGpp present in all slow-growing amino acid-limited cultures (relaxed and stringent) demonstrated that only basal levels of ppGpp were made. These data are consistent with the hypothesis that when growth is limited in the chemostat by an initiation event in protein synthesis, i.e., limited methionine, RNA regulation occurs in relaxed as well as stringent strains. Also, when other amino acids are limiting in concentration during translation, errors occur in relaxed strains, resulting in misread proteins.

Amino Acids↗
PubMed2003

Dedifferentiation of primary spermatocytes into germ cell tumors in C. elegans lacking the pumilio-like protein PUF-8.

PUF proteins are a conserved family of RNA binding proteins that regulate RNA stability and translation by binding to specific sequences in 3'-untranslated regions. Drosophila PUMILIO and C. elegans FBF are essential for self-renewal of germline stem cells, suggesting that a common function of PUF proteins may be to sustain mitotic proliferation of stem cells. Here, we show that PUF-8, the C. elegans PUF most related to PUMILIO, performs a different function in germ cells that have begun meiosis: in primary spermatocytes, puf-8 is required to maintain meiosis and prevent the return to mitosis. Primary spermatocytes lacking PUF-8 complete meiotic prophase but do not undergo normal meiotic divisions. Instead, they dedifferentiate back into mitotically cycling germ cells and form rapidly growing tumors. These findings reveal an unexpected ability for germ cells that have completed meiotic prophase to return to the mitotic cycle, and they support the view that PUF proteins regulate multiple transitions during germline development.

Animals↗
PubMed1997

Dietary fat saturation effects on low-density-lipoprotein concentrations and metabolism in various animal models.

Saturated vegetable oils (coconut, palm, and palm kernel oil) and fats (butter and lard) are hypercholesterolemic relative to monounsaturated and polyunsaturated vegetable oils. The increase in plasma low-density-lipoprotein-cholesterol (LDL-C) concentrations associated with consumption of saturated vegetable oils and fats is largely explained by a decrease in hepatic LDL receptor activity and an increase in the LDL-C production rate. Hepatic LDL receptor activity may be regulated by the messenger RNA concentration of the LDL receptor. The decrease in hepatic LDL receptor activity with saturated fat feeding is associated with decreased hepatic sterol O-acyltransferase activity and, therefore, a reduced inert pool of cholesteryl ester. A putative regulatory pool of cholesterol is increased with saturated fat feeding and suppresses LDL receptor activity, possibly through hepatic messenger RNA regulation. For most studies, an independent effect of a vegetable oil or fat could not be ascertained because there was no neutral control and at least two of the test oils or fats were varied. Animal data for the effects of individual fatty acids on plasma LDL-C concentrations and metabolism are sparse. The evidence suggests that caproic acid (6:0), caprylic acid (8:0), and capric acid (10:0) are neutral with respect to their LDL-C-raising properties and their ability to modulate LDL metabolism. Lauric acid (12:0), myristic acid (14:0), and palmitic acid (16:0) are approximately equivalent in their LDL-C-raising potential by reducing hepatic LDL receptor activity and increasing the LDL-C production rate, apparently via modulation of sterol O-acyltransferase activity. Stearic acid (18:0) appears to be neutral in its LDL-C-raising potential and how it affects LDL metabolism.

Animals↗
PubMed2000

U-turns and regulatory RNAs.

Conventional antisense RNAs, such as those controlling plasmid replication and maintenance, inhibit the function of their target RNAs rapidly and efficiently. Novel findings show that a common U-turn loop structure mediates fast RNA pairing in the majority of these RNA controlled systems. Usually, an antisense RNA regulates a single, cognate target RNA only. Recent reports, however, show that antisense RNAs can act as promiscuous regulators that control multiple genes in concert to integrate complex physiological responses in Escherichia coli.

Base Pairing↗
PubMed2007

BRCA1 does not paint the inactive X to localize XIST RNA but may contribute to broad changes in cancer that impact XIST and Xi heterochromatin.

The BRCA1 tumor suppressor involved in breast and ovarian cancer is linked to several fundamental cell regulatory processes. Recently, it was reported that BRCA1 supports localization of XIST RNA to the inactive X chromosome (Xi) in women. The apparent cytological overlap between BRCA1 and XIST RNA across the Xi raised the possibility a direct role of BRCA1 in localizing XIST. We report here that BRCA1 does not paint the Xi or XIST territory, as do markers of Xi facultative heterochromatin. A smaller BRCA1 accumulation abuts Xi, although this is not exclusive to Xi. In BRCA1 depleted normal and tumor cells, or BRCA1 reconstituted cells, BRCA1 status does not closely correlate with XIST localization, however in a BRCA1 inducible system over-expression correlated strongly with enhanced XIST expression. We confirm frequent loss of an Xi in tumor cells. In addition to mitotic loss of Xi, we find XIST RNA expression or localization frequently become compromised in cultured breast cancer cells, suggesting Xi heterochromatin may not be fully maintained. We demonstrate that complex epigenetic differences between tumor cell subpopulations can have striking effects on XIST transcription, accumulation, and localization, but this does not strictly correlate with BRCA1. Although BRCA1 can have indirect effects that impact XIST, our results do not indicate a direct and specific role in XIST RNA regulation. Rather, regulatory factors such as BRCA1 that have broad effects on chromatin or gene regulation can impact XIST RNA and the Xi. We provide preliminary evidence that this may occur as part of a wider failure of heterochromatin maintenance in some cancers.

BRCA1 Protein↗
PubMed1978

Studies on the regulation of RNA synthesis in neuronal and glial nuclei isolated from rat brain.

In searching for regulatory mechanisms involved in the cell-specific neuronal and glial transcription a cell-free transcriptional system has been developed using neuronal and glial rat brain chromatin and partially purified neuronal and glial nuclear rat brain RNA polymerases. Both free and chromatin-bound (engaged) neuronal and glial RNA polymerase fractions were separated from isolated neuronal and glial rat brain nuclei to determine their transcriptive efficiency. A double number of RNA initiation sites was measured on the neuronal when compared to the glial chromatin, independently of whether the neuronal or the glial RNA polymerase preparation was used for the determination. Structural modification of the neuronal and glial chromatin template by acetylation with acetyl-coenzyme A leads to an increase of the total number of RNA initiation sites available for exogenously added rat brain RNA polymerase. This indicates that acetylation of chromatin-bound proteins is capable to render primarily restricted gene sequences transcriptable. A positive correlation exists between the extent of acetate uptake by neuronal and glial chromatin-bound histone fractions and the extent of the increase of the number of RNA initiation sites is specifically related to histone acetylation rather than to acetylation of any other chromatin protein. Significant information in this respect could be achieved by dissociation of chromatin into its principal components and selectively reconstituting DNA with specifically acetylated histone and non-histone proteins.

Animals↗
PubMed1977

The regulation of RNA synthesis in yeast. I: Starvation experiments.

The synthesis of tRNA in yeast is shown to be under separate control to that of rRNA during amino acid and nitrogen starvation. Inhibitors of the elongation and termination steps of protein synthesis were found to stimulate the synthesis of tRNA in starved yeast cells. This effect appeared to be due to the "trickle-charging" of tRNA. Two inhibitors of early steps in the initiation of protein synthesis were found to be unable to stimulate RNA synthesis in starved cells. It is proposed that yeast tRNA synthesis is under autoregulatory control and that the level of tRNA charging and the mRNA-ribosome complex are important components of this control system.

Amino Acids↗
PubMed1979

Regulation of RNA synthesis in yeast. III. Synthesis during the cell cycle.

Centrifugal elutriation was used to separate cells in different stages of the cell cycle from a culture of Saccharomyces cerevisiae in balanced exponential growth. The rate of DNA and RNA synthesis was determined using a pulse--long-term label technique that is capable of distinguishing between exponential, linear, and periodic variations in the rate of synthesis through the cell cycle. It was found that while the rate of DNA synthesis varies periodically through the cell cycle, the rate of synthesis of mRNA, rRNA, and tRNA increases exponentially through the cell cycle. The implications of these findings for the control of RNA synthesis are discussed.

Cell Cycle↗