Pre-4S RNA made in isolated HeLa cell nuclei terminates with U

Mechanism of enhanced RNA synthesis in acute-phase rat liver and its relationship to chromatin structure

Nuclei isolated from the liver of rats undergoing an acute inflammatory reaction induced by turpentine treatment show increased RNA synthesis. This increase is essentially determined by a faster polyribonucleotide-elongation rate while the number of transcribing polymerase molecules is unchanged. The sensitivity of chromatin to micrococcal-nuclease digestion and the composition of chromosomal proteins are not affected by the acute-phase process. Therefore the increased RNA synthesis by liver nuclei from acutely inflamed rats does not seem to correlate with major changes in chromatin structure.

RNA synthesis and number of transcribing polymerase molecules in ischemic liver nuclei

Nuclei isolated from ischemic liver show a consistent reduction of their RNA synthesis. The reduction persists at high ionic strength and in the presence of heparin, when RNA synthesis in vitro is fully activated and occurs in the presence as well as in the absence of alpha-amanitin. Both the number of transcribing polymerase molecules and the rate of elongation of initiated polynucleotide chains seem to be equally affected.

Stimulation in vitro of a heparin-resistant RNA polymerase I transcription complex

A soluble factor partially purified from calf liver increases transcription by RNA polymerase I in isolated nuclei. Addition of the factor to reactions which have reached a plateau owing to the inability to reinitiate on the endogenous chromatin template restores the initial rate of synthesis and stimulates an increased accumulation of RNA product. The RNA synthesis stimulated by factor addition is identical with that initiated in vivo in that it is resistant to heparin disruption.

RNA synthesis by nuclei and nucleoli from ischemic liver cells

Nuclei and nucleoli were isolated from rat livers subjected to an interruption of the blood supply for periods of different duration, as well as after restoration of the blood supply. They were assayed for RNA synthesis under conditions of diverse ionic strengths, and in the presence of an exogenous template, such as poly d (A-T), and actinomycin to inactivate the endogenous template; alpha-amanitin was made used of to distinguish polymerase I and polymerase II dependent RNA synthesis. Nuclei and nucleoli from ischemic livers showed a severe impairment of RNA synthesis, which is likely to be due to decreased initiation frequency of the engaged polymerases, while free polymerases were essentially unchanged. Both form I and II polymerase were equally involved. After restoration of the blood supply RNA synthesis recovered with an overshooting well above normal levels of activity, lasting for at least 24 hours. Increased RNA synthesis was not followed by thymidine incorporation into DNA.

Size of primary transcripts in Ehrlich ascites cells as measured by tetraphosphate determination

A method for the quantitation of 5"-tetraphosphate ends in 32P-labeled RNA has been developed. The tetraphosphate content of different RNA fractions obtained from Ehrlich ascites cells labeled with 32P for different lengths of time has been determined. Ribosomal RNA and poly(U)-binding RNA, labeled for long periods, (mRNA) lack 5'-terminal tetraphosphate. 5S RNA, pulse labeled 4-5S RNA, and poly(U)-binding hnRNA (heterogeneous nuclear RNA) do contain tetraphosphate. From the amount of the tetraphosphate, molecular weight data can be calculated for these RNA fractions which agree with independent determinations by denaturing gel electrophoresis. The results demonstrate that the majority of the poly(A) containing hnRNA molecules are small (less than 28S) and contain the tetraphosphate of the primary transcript. Therefore, they do not originate from the 3'-end of large molecules by processing events.

HeLa cell deoxyribonucleic acid dependent RNA polymerases: function and properties of the class III enzymes

The class III DNA dependent RNA polymerases (nucleoside triphosphate:RNA nucleotidyltransferase EC 2.7.7.6 from HeLa cells have been solubilized and characterized as to function and properties. Two chromatographically distinct forms of enzyme III, designated polymerases IIIA and IIIB, can be resolved when cell extracts are chromatographed on DEAE-Sephadex columns. Enzymes IIIA and IIIB exhibit nearly identical catalytic properties such as divalent cation stimulation, broad biphasic ammonium sulfate optima, and characteristic alpha-amanitin sensitivities which clearly distinguish them from the homologous enzymes, forms I and II. Polymerases IIIA and IIIB are both primarily localized in the nucleus (greater than 60%). The most notable characteristic of the class III enzymes is a unique sensitivity to inhibition by alpha-amanitin (50% inhibition at 15 mug/ml). HeLa cell enzyme I is not inhibited by the mushroom toxin even at very high concentrations (greater than 400 mug/ml), while HeLa cell polymerase II is inhibited by very low concentrations of amanitin (50% inhibition at 0.003 mug/ml). The three major classes of enzyme (I, II, III) exhibit characteristic sensitivities to alpha-amanitin whether assayed in nuclei, crude homogenates, or in a chromatographically purified state. Using a nuclear in vitro RNA synthesizing system to investigate the alpha-amanitin sensitivities of the synthesis of tRNA precursor (4.5S pre-tRNA) and 5S ribosomal RNA, it was found that the synthesis of these RNA species was inhibited 50% at 15 mug/ml of alpha-amanitin. The alpha-amanitin inhibition curves for the synthesis of pre-tRNA-5S ribosomal RNA in nuclei and the alpha-amanitin titration curves for the partially purified class III enzymes (IIIA and IIIB) are identical. These data, therefore, show that the in vivo functional role of the class III RNA polymerases (IIIA-IIIB) is the transcription of the genes coding for transfer RNA and 5S ribosomal RNA.

Control of nucleolar RNA synthesis by the intracellular pool sizes of ATP and GTP

The influence of amino acid starvation on both the pool sizes of nucleoside triphosphates and the rRNA synthetic capacity of Ehrlich ascites cells was studied. The results indicate that under shiftdown conditions, an immediate shrinkage of the cellular ATP and GTP levels occurs. Concomitant with this, protein and rRNA syntheisis are markedly inhibited. If the pool sizes of purine nucleaside triphosphates are expanded by adding adenosine or guanosine to cells cultured in histidine-free medium, the nucleolar RNA synthesis is fully restored, while protein synthesis remains inhibited. The results suggest that the rate of pre-rRNA transcription may be controlled by the actual nucleoside triphosphate levels of the cells rather than by short-lived protein(s), as has been previously postulated.

Amino acid starvation affects the initiation frequency of nucleolar RNA polymerase

The synthesis of ribosomal precursor RNA in mouse ascites nucleoli derived from cells starved for amino acids is compared with the activity of nucleoli from control cells cultivated in the presence of all amino acids. It is shown that deprivation of a single essential amino acid from the culture medium results in a drastic decrease of the RNA-forming capacity of the isolated nucleoli by a factor of 2-3. This switchoff in rRNA synthesis is a very fast process. Half-maximal inactivation occurs after only 30 min. Addition of amino acids to starved cells leads to a rapid recovery, which is reflected by a sharp increase in the RNA polymerase activity of the isolated nucleoli. Studies on the molecular mechanism of this amino acid-mediated control of rRNA synthesis indicate that this effect is not caused by different growth rates of the RNA chains, but rather by an altered initiation frequency of the RNA polymerase in vivo. Whereas in nucleoli derived from cells grown in full medium almost all the polymerase is tightly bound in a transcriptional complex, a high amount of "free" polymerase which becomes active after addition of exogenous template is present in nucleoli from starved cells.

Adrenocorticotropic hormone stimulation of adrenal RNA polymerase I and III activities. Nucleotide incorporation into internal positions and 3' chain termini

In the presence of 50 mM (NH4)2SO4 and low concentrations of alpha-amanitin (7.7 mug/ml), adrenal nuclei synthesize predominately rRNA as characterized by size and base composition. Approximately 10% of the RNA synthesized under these conditions sediments at 4-5 S; this RNA synthesizing activity is inhibited by high concentrations of alpha-amanitin (231 mug/ml) indicating the presence of RNA polymerase III activity. ACTH administration to guinea pigs results in a twofold increase in adrenal nuclear RNA polymerase I and III activities at 14 hr of hormone treatment. Analysis of the amount of radiolabeled nucleoside triphosphate incorporated in vitro into 3' chain termini and into internal nucleotide positions has been utilized to measure the number of RNA chains and the average chain length synthesized in vitro. Incorporation into 3' chain termini is not changed by ACTH; incorporation into internal nucleotides is doubled in parallel with the increase in RNA polymerase I activity. These results are not due to an altered Km of RNA polymerase I for the four nucleoside triphosphates, nor to differential R Nase or phosphatase activity. These studies suggest that the regulation of RNA polymerase I by ACTH is accomplished in part through an increase in the rate of RNA chain elongation.