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At least 127 records · Page 7Linked to original sources
PubMed1969

The mechanism of messenger RNA translocation through ribosomes.

The two recognized enzymatic steps involved in the extension of peptides on ribosomes of the 80S type have been studied in a highly purified transfer system derived from rabbit reticulocytes. Data presented are interpreted to reflect three ribosomal binding sites through which transfer RNA is moved in two independent enzymatic reactions each of which requires guanosine 5'-triphosphate hydrolysis. The binding enzyme facilitates translocation between the entry and acceptor ribosomal sites. Transferase II is involved in translocation between the acceptor and donor ribosomal sites. A model is proposed to account for movement of transfer RNA and messenger RNA between the ribosomal sites.

Animals↗
PubMed1975

Biosynthesis of mouse interferon by translation of its messenger RNA in a cell-free system.

A fraction of mouse RNA containing messenger RNA coding for mouse interferon was translated with high efficiency in a wheat germ system into a fully active product. This product fulfills the criteria for mouse interferon, namely: (1) it was active against vesicular stomatitis virus and herpes simplex virus in mouse cells; (2) its antiviral activity was species specific; (3) its activity was completely neutralized by mouse anti-interferon serum. The synthesis of interferon in this cell-free system requires the presence of spermine.

Antigen-Antibody Reactions↗
PubMed2003

How bacterial ribosomal protein L20 assembles with 23 S ribosomal RNA and its own messenger RNA.

In bacteria, the expression of ribosomal proteins is often feedback-regulated at the translational level by the binding of the protein to its own mRNA. This is the case for L20, which binds to two distinct sites of its mRNA that both resemble its binding site on 23 S rRNA. In the present work, we report an NMR analysis of the interaction between the C-terminal domain of L20 (L20C) and both its rRNA- and mRNA-binding sites. Changes in the NMR chemical shifts of the L20C backbone nuclei were used to show that the same set of residues are modified upon addition of either the rRNA or the mRNA fragments, suggesting a mimicry at the atomic level. In addition, small angle x-ray scattering experiments, performed with the rRNA fragment, demonstrated the formation of a complex made of two RNAs and two L20C molecules. A low resolution model of this complex was then calculated using (i) the rRNA/L20C structure in the 50 S context and (ii) NMR and small angle x-ray scattering results. The formation of this complex is interesting in the context of gene regulation because it suggests that translational repression could be performed by a complex of two proteins, each interacting with the two distinct L20-binding sites within the operator.

Bacterial Proteins↗
PubMed1990

Gonadotropin subunit messenger RNA concentrations after blockade of gonadotropin-releasing hormone action: testosterone selectively increases follicle-stimulating hormone beta-subunit messenger RNA by posttranscriptional mechanisms.

Regulation of gonadotropin gene expression by sex steroids may occur via direct effects on the pituitary and/or indirect effects of steroids mediated through hypothalamic GnRH. We aimed to define the effects of testosterone (T) on alpha, LH beta, and FSH beta mRNA expression in the male rat after blockade of GnRH action on the gonadotrope. A water-soluble GnRH antagonist was administered iv to castrate male rats (increased endogenous GnRH secretion) and to castrate T-replaced rats in which gonadotropin subunit mRNAs had been increased by prior treatment with exogenous GnRH pulses. In castrate male rats, GnRH antagonist resulted in a fall in all three subunit mRNAs. Alpha and LH beta declined at slower rates (half-disappearance after 50 and 65 h, respectively), and neither fell to values present in intact rats over 84 h. In contrast, FSH beta mRNA declined more rapidly, with a half-disappearance after 20 h. In castrate T-replaced rats, alpha mRNA declined at a rate similar to that in castrates (half-disappearance after 50 h). LH beta declined more slowly, and the rate of FSH beta decline was markedly prolonged in the presence of T (half-disappearance time increased from 20 to 50 h). These results suggest that T exerts direct effects on FSH beta transcription or mRNA stability which are independent of GnRH action. To assess these possibilities, a long-acting GnRH antagonist (Detirelix) was administered to castrate male rats, which also received T or sham implants 4 days after castration. FSH beta mRNA levels fell during the 4 days of Detirelix alone, but the addition of T on day 4 resulted in a 2-fold rise in FSH beta mRNA, restoring FSH beta mRNA to levels present in intact rats. Serum FSH closely paralleled FSH beta mRNA concentrations. Alpha mRNA was reduced by 25%, and LH beta mRNA concentrations were unchanged in the presence of T. The rate of alpha mRNA transcription was markedly reduced and that of LH beta tended to fall in T-treated rats, but T had no significant effect on the FSH beta transcription rate. Thus, the action of T to increase concentrations of cytosolic FSH beta mRNA appears to be exerted at a posttranscriptional level, possibly via effects of T on FSH beta mRNA stability. This may represent a mechanism by which T can effect differential regulation of gonadotropin subunit mRNA concentrations.

Amino Acid Sequence↗
PubMed1980

Changes in polysomal polyadenylated RNA and alpha-fetoprotein messenger RNA during hepatocarcinogenesis.

Polysomal polyadenylated RNA was isolated from preneoplastic and neoplastic livers obtained from rats kept on a choline-deficient diet containing ethionine for 8 and 25 to 32 weeks, respectively. Normal, preneoplastic, and neoplastic liver polysomal messenger RNA's (mRNA's) were hybridized with homologous and heterologous 3H-labeled complementary DNA's (cDNA's). The results show that, in terms of RNA mass, all or most of the polysomal polyadenylated RNA present in preneoplastic or neoplastic liver is also present in normal liver. This was induced by the similar extent of hybridization between [3H]cDNA transcribed from preneoplastic or neoplastic liver mRNA's with their homologous mRNA's and with mRNA from normal liver. Conversely, most or all of the polysomal polyadenylated RNA of normal liver is also found in preneoplastic and neoplastic livers, as indicated by the extent of hybridization of [3H]cDNA transcribed from normal liver with mRNA's from normal, preneoplastic, and neoplastic livers. Shifts in the relative abundance of mRNA sequences were detected in the polysomal mRNA of preneoplastic livers and especially in the mRNA of neoplastic liver. Hybridization of alpha-fetoprotein cDNA with liver polyadenylated RNA showed a substantial increase in alpha-fetoprotein mRNA content after 8 and 15 weeks of feeding the carcinogenic diet. Similar experiments using globin cDNA failed to show an increase in globin mRNA content in preneoplastic livers.

Animals↗
PubMed1973

Mitochondrial protein synthesis: RNA with the properties of Eukaryotic messenger RNA.

A heterogeneous RNA fraction with properties resembling those of messenger RNA was identified in mammalian mitochondria. Synthesis of contaminating RNA of nuclear origin was suppressed by treatment with camptothecin. Labeling of the messenger-like RNA is completely inhibited by ethidium bromide, a specific inhibitor of mitochondrial functions.Although mitochondrial protein synthesis resembles that of prokaryotes in several regards, the messenger-like RNA is covalently linked to poly(adenylic acid) [poly(A)]. Poly(A) has thus far been found only in eukaryotic cells. The poly(A) segment has a gel electrophoretic mobility of about 4 S, corresponding to a length of 50-80 nucleotides, and thus resembles in size the poly(A) found in some mammalian viral RNAs. The messenger RNA can be released from the mitochondrial protein-synthesizing structure by treatment with puromycin.

Adenine↗
PubMed1980

Cell-free synthesis of the myelin basic proteins in a wheat germ system programmed with brain messenger RNA.

Poly A(+) messenger RNA (mRNA) was isolated from the brains of 3-week-old mice and translated in a cell-free system derived from wheat germ. Maximal stimulation of the system by brain mRNA was observed at a relatively low K+ concentration (45 mM) and low mRNA concentration (1-10 microgram/ml). The translational system was dependent on an energy-generating system and stimulated by the addition of spermidine and transfer RNA. Under optimal conditions, incorporation was linear for almost 45 min, but the overall stimulation with brain mRNA was relatively low (about twofold). In spite of the low stimulation, analysis of the translation products indicated that in the presence of brain mRNA polypeptides which co-chromatographed and co-electrophoresed with the two mouse myelin basic proteins could be detected. In control experiments with liver poly A(+) mRNA, which stimulated the translational system to a greater extent than brain mRNA, no such polypeptides could be detected. In this system the ratio of synthesis of small myelin basic protein to large myelin basic protein was found to be about 4.0, which correlates well with that found in vivo.

Animals↗
PubMed2003

Crystal structure of the transfer-RNA domain of transfer-messenger RNA in complex with SmpB.

Accurate translation of genetic information into protein sequence depends on complete messenger RNA molecules. Truncated mRNAs cause synthesis of defective proteins, and arrest ribosomes at the end of their incomplete message. In bacteria, a hybrid RNA molecule that combines the functions of both transfer and messenger RNAs (called tmRNA) rescues stalled ribosomes, and targets aberrant, partially synthesized, proteins for proteolytic degradation. Here we report the 3.2-A-resolution structure of the tRNA-like domain of tmRNA (tmRNA(Delta)) in complex with small protein B (SmpB), a protein essential for biological functions of tmRNA. We find that the flexible RNA molecule adopts an open L-shaped conformation and SmpB binds to its elbow region, stabilizing the single-stranded D-loop in an extended conformation. The most striking feature of the structure of tmRNA(Delta) is a 90 degrees rotation of the TPsiC-arm around the helical axis. Owing to this unusual conformation, the SmpB-tmRNA(Delta) complex positioned into the A-site of the ribosome orients SmpB towards the small ribosomal subunit, and directs tmRNA towards the elongation-factor binding region of the ribosome. On the basis of this structure, we propose a model for the binding of tmRNA on the ribosome.

Bacterial Proteins↗
PubMed1991

Requirement of microfilaments in sorting of actin messenger RNA.

Specific messenger RNAs (mRNAs) can be sequestered within distinct cellular locations, but little is known about how this is accomplished. The participation of the three major cellular filaments in the localization of actin mRNA was studied in chicken embryo fibroblasts. Movement of actin mRNA to the cell periphery and maintenance of that regionalization required intact microfilaments (composed of actin) but not microtubules or intermediate filaments. The results presented here suggest that actin-binding proteins may participate in mRNA sorting.

Actin Cytoskeleton↗
PubMed1992

Inhibitors of RNA and protein synthesis stabilize messenger RNA for the RII beta subunit of protein kinase A in different cellular compartments.

Messenger RNA for RII beta is transiently induced (greater than 50-fold) by cAMP analogs in primary cultures of rat Sertoli cells. The induction is dependent on protein synthesis. We have previously shown that mRNA for RII beta is stabilized by cAMP, as well as inhibitors of transcription and translation. This indicated that rapid degradation of RII beta mRNA involved a protein with a rapid turnover and its corresponding mRNA. The two RNA synthesis inhibitors used in the present study stabilized both nuclear and cytoplasmic RII beta mRNA, whereas inhibition of protein synthesis stabilized RII beta mRNA in the cytoplasm only. These results indicate that only cytoplasmic degradation of RII beta mRNA is dependent on a protein with high turnover. In contrast, nuclear degradation appears to be dependent on an RNA with a short half-life, not involving protein synthesis.

Animals↗
PubMed1974

Cell-free transcription of mammalian chromatin: transcription of globin messenger RNA sequences from bone-marrow chromatin with mammalian RNA polymerase.

A mammalian cell-free transcriptional system was developed in which mammalian RNA polymerase synthesizes globin messenger RNA sequences from bone-marrow chromatin. The messenger RNA sequences are detected by measurement of the ability of the transcribed RNA to hybridize with globin complementary DNA. The globin complementary DNA is synthesized by the enzyme from avian myeloblastosis virus, RNA-directed DNA polymerase, with purified globin messenger RNA as template. The specificity of the globin complementary DNA in annealing reactions was verified by preparing DNA complementary to liver messenger RNA and showing that the globin and liver complementary DNAs are specific for their own messenger RNAs. Both DNA-dependent RNA polymerase II from sheep liver and RNA polymerase from Escherichia coli can transcribe globin messenger RNA sequences from rabbit bone-marrow chromatin; however, the mammalian enzyme appears to be more specific in that globin gene sequences represent a higher proportion of the RNA synthesized. Neither polymerase can transcribe globin messenger RNA sequences from rabbit-liver chromatin. This cell-free assay system should be useful in searching for mammalian transcriptional regulatory factors.

Animals↗
PubMed1979

Effects of ionizing radiation and partial hepatectomy on messenger RNA synthesis.

Newly synthesized messenger RNA, as measured by a 40 min uptake of the radioactive precursor (6-14C) orotic acid, was studied in the regenerating livers of non-irradiated and gamma-irradiated (1800 rad) adrenal-intact and adrenalectomized rats 24 aand 48 hours after partial hepatectomy. Two groups of rats, one with and one without adrenal glands, were each divided into four subgroups: (1) control rats, (2) irradiated rats, (3) partially hepatectomized rats and (4) irradiated, partially hepatectomized rats. The radioactive profile of polyribosome formation and distribution was determined by sucrose density gradient centrifugation (10--40 per cent). The result of this study indicates that ionizing radiation decreases the synthesis of newly formed messenger RNA in re generating livers of adrenal-intact rats. However, adrenalectomy largely abolished that inhibition. These data suggest that the decrease in messenger RNA synthesis may be explained by the disturbance of adrenal hormones induced by partial hepatectomy and ionizing radiation.

Adrenal Glands↗