Effects of ionic strength on the RNA polymerase activities of isolated nuclei and nucleoli of rat liver

The use of rat liver nucleoplasm for the characterization of heterogeneous nuclear ribonucleic acid synthesis in vitro

1. A nucleoplasmic fraction rich in endogenous RNA polymerase II activity was isolated from rat liver nuclei and conditions were determined under which elongation of RNA molecules initiated in vivo continued at maximal rates in vitro. 2. Elongation rates in vitro were calculated to be about 0.25 nucleotide/s and there were about 7 X 10(3) RNA molecules in the process of being elongated by form-II RNA polymerase per original nucleus. 3. Evidence was obtained suggesting that transcription-dependent release of RNA polymerase II molecules from the template occurred during the incubations in vitro. 4. The nascent RNA was tightly associated with protein and banded as ribonucleoprotein in caesium salt gradients. 5. RNA molecules labelled in vitro were up to 13000 nucleotides in length, but consisted of long unlabelled chains transcribed in vivo with only short labelled sequences added in vitro, and without significant polyadenylation. 6. Hybridization of transcripts in the presence of a vast excess of DNA demonstrated that both form-II RNA polymerase and another enzyme, resistant to low alpha-amanitin concentrations, were synthesizing RNA molecules complementary to both reiterated and unique DNA sequences in the genome.

Mechanism of the stimulation of RNA synthesis in rat liver nuclei by silybin

The influence of the flavonolignane derivatives silybin, silybinhemisuccinate and silybindihemisuccinate on the RNA synthesis in isolated nuclei from rat livers was studied. A stimulatory effect of silybin on the incorporation of [3H]UTP into nuclear RNA was found and the dose dependence could be demonstrated. The results support former findings that silybin stimulates RNA synthesis in rat livers in vivo and in hepatocytes. Experiments with purified nucleoli indicated that mainly the rate of rRNA synthesis is increased. The mechanism of this stimulation was elucidated by experiments with isolated RNA polymerases. It could be demonstrated that polymerase B is not affected by the flavonolignane, but the activity of polymerase A is increased, due to higher V at constant Km values. Thus silybin is shown to be an enzyme-stimulating effector.

In vitro transcription by isolated nuclei of Rhynchosciara americana salivary glands. Characteristics of incorporation and inhibition by alpha-amanitin

A method for the isolation of polytene nuclei from salivary glands cells of the Diptera Rhynchosciara americana is described. The stage-specific morphological pattern of the chromosome is maintained during the isolation. The isolated nuclei show two distinct RNA polymerase activities, namely I and II, characterized on the basis of ionic requirements and alpha-amanitin sensitivity. Studies of the product under the incubation conditions show that the system allows the synthesis of high-molecular weight RNA, beside a low molecular weight peak which may comprise pre-4S and 5S RNAs. Autoradiographic studies carried out in the presence or absence of the toxin alpha-amanitin showed that micronucleoli contain products of RNA polymerase type I activity (ribosomal RNA) and that the DNA puffs are engaged in alpha-amanitin sensitive RNA synthesis and thus are sites of polymerase type II activity.