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A Tigyi

Publications and source records attributed to A Tigyi.

At least 37 records · Page 2Linked to original sources
PubMed1982

Influence of 3-methylcholanthrene on liver nucleolar and nucleoplasmic activities of protein kinases and RNA polymerases.

The experiments were designed to investigate some details of the action of 3-methylcholanthrene (3-MC) on the regulation of transcription. After a single intraperitoneal dose of 3-MC a significant increase in the activities of both nucleolar and nucleoplasmic protein kinases in hepatic cells of young rats was found. The maximal stimulation took place 24 hr after the administration of 3-MC and the extent of activation was much greater in the nucleolar fraction. There is a significant elevation of the activities of both functional forms, free and template-engaged, of RNA polymerase A 24 hr after a single injection of 3-MC. Free and engaged forms of extranucleolar RNA polymerase B show a different behaviour: after 24 hr of 3-MC administration the engaged form is markedly enhanced while the activity of the free enzyme shows a significant decrease. The more moderate increase in total RNA polymerase B activity is obviously preceded by a transfer of the enzyme from 'free' to 'engaged' form. Since the enhancement of protein kinase activities was accompanied by the stimulation of nuclear RNA polymerases we suggest that both kinds of enzymes are involved in an epigenetic mechanism of the inducing action of 3-MC on cytochrome P1-450.

Animals↗
PubMed1981

Structural characterization of polysomal poly(A)-protein particles in rat liver.

Poly(A)-protein particles were prepared from rat liver polyribosomes, washed with 0.5 M KCl or unwashed, after digestion with pancreatic ribonuclease and ribonuclease T1 by two successive rounds of sucrose gradient centrifugation. The particles were sedimented in a range of 5--13 S with a peak at about 9 S. The KCl wash of polysomes had no effect on the sedimentation properties of the particles. The particles isolated in this manner were 99% resistant to further pancreatic ribonuclease treatment and contained about 96% adenylic acid. The length of the poly(A) molecules prepared from the poly(A)-protein particles showed a broad distribution of about 70--290 nucleotides with a peak around 130 nucleotides, as measured by polyacrylamide gel electrophoresis. In CsCl density gradient the poly(A)-protein particles banded in a density range of 1.30--1.42 g/cm3 with a peak at 1.36 g/cm3, which amounts to about 80% of the protein content. Sodium dodecyl sulfate/polyacrylamide and urea/sodium dodecyl sulfate/polyacrylamide gel electrophoresis demonstrated six polypeptides with molecular weights of 50 000, 54 000, 58 000, 63 000, 76 000 and 90 000 in the poly(A)-protein particles, but the main components were dependent on the method. The treatment of polysomes with KCl resulted in a loss of the 90 000-molecular-weight component. Amino acid analysis of the polypeptides bound to poly(A) revealed that they contained a relatively large amount of aspartic plus glutamic acid (21.6%) as well as hydrophobic amino acids (41.4%). Digestion of glutaraldehyde-fixed particles with ribonuclease T2 showed that about 50% of poly(A) was accessible to the enzyme, thus this part of poly(A) was located on the surface of the particles. In the electron micrographs the shadowed poly(A)-protein particles appeared in a globular, somewhat elongated form and were mostly 14-18 nm in diameter. On the basis of the results a model for the 'average' 9-S particles was constructed.

Animals↗
PubMed1981

Studies on the structure of rat liver messenger ribonucleoprotein. I. Isolation and characterization.

Messenger ribonucleoprotein (mRNP) was released from 0.5 M KCl washed rat liver polyribosomes after mild pancreatic ribonuclease (EC 3.1.27.5) and EDTA treatment and separated by sucrose gradient centrifugation from ribosomal subunits. The method yielded partially fragmented mRNP, which, however, was free from ribosomal contaminants. In CsCl gradient the mRNP banded at 1.46 g/cm3, indicating a protein content of about 65%. Treatment of mRNP with 0.25 M or 0.5 M KCl resulted in loss of the proteins. Urea/sodium dodecyl sulfate polyacrylamide gel electrophoresis of mRNA bound proteins showed that the most prominent polypeptides found in the mRNP fractions exhibited molecular weights of 29 000 (P29), 31 000 (P31), 38 000 (P38), 44 000 (P44), 50 000 (P50), 54 000 (P54), 63 000 (P63) 76 000 (P76) and 105 000 (P105). Three polypeptides, P38, P44 and P63 were most sensitive to high salt treatment.

Animals↗
PubMed1981

Studies on the structure of rat liver messenger ribonucleoprotein. II. Non-poly(A) RNase resistant fragments and electron microscopic appearance of mRNP.

Partially fragmented 12-21S rat liver messenger ribonucleoprotein (mRNP), labelled either with [3H]-orotic acid or [3H]-adenine was treated with 5 (micrograms/ml or 0.1 microgram/ml pancreatic ribonuclease (EC 3.1.27.5) and the resistant fragments were separated by sucrose gradient centrifugation. Two types of fragments were obtained. Digestion of mRNP with ribonuclease at a concentration of 5 micrograms/ml resulted in 9S poly(A)-protein particles of mRNP as evidenced by their characteristic sedimentation, electrophoretic mobility of the RNA moiety and protein composition. In contrast, ribonuclease at a concentration of 0.1 microgram/ml produced 2-5S pyrimidine labelled fragments carrying polynucleotide sequences consisting of approximately 16-50 residues. Two polypeptides of rat liver mRNP with molecular weights of 38 000 (P38) and 44 000 (P44) were found to be attached to these sequences. The data demonstrate that RNA sequences other than poly(A) interact with protein in mRNP. Electron microscopic studies revealed that the liberation of mRNP from the polysomes by EDTA changes its surface properties since EDTA releases the mRNP mainly in the form of globular particles. However, a small proportion of the mRNP remains in fibril-like form. Among the fibrils several blobs could be seen which were probably the proteins attached to the mRNA. From the available data a model for the structure of an "average" mRNP molecule is proposed.

Animals↗
PubMed1980

Hepatic nuclear free and engaged RNA-polymerases in young rats pretreated with 3-methylcholanthrene.

In 3-methylcholanthrene (3-MC)-pretreated young rats the free and engaged RNA polymerases were investigated in detail both in the nucleolar and nucleoplasmic fractions. Both functional forms of the nucleolar RNA polymerase (A) show a great stimulation. The maximum increase of the free form up to 235% compared with controls is obtained 24 h after 3-MC administration. The engaged fraction reaches its maximum later. The extranucleolar RNA polymerase (B) in its engaged form shows the maximum effect (160%) after 24 h, whereas the free form is at first diminished and later on increases steadily. The activation of RNA polymerase A and the interconversion process between the free and engaged form of RNA polymerase B seem to play a significant role in the 3-MC-mediated induction.

Amanitins↗
PubMed1980

Effect of 3-methylcholanthrene on RNA polymerase and protein kinase activities and on the nuclear ultrastructure of rat liver.

The polycyclic aromatic hydrocarbon 3-methylcholanthrene (3-MC) is a well known inducer of the microsomal mixed function oxidase enzyme system in rat liver cells. It seems probable that the inductive action of 3-MC is realized, at least partly, at the transcriptional level of protein synthesis regulation. The present experiments indicated that in the liver of young rats there was a significant alteration in the activities of nucleolar as well as nucleoplasmic protein kinase and RNA polymerase enzymes during the first days of exposure to a single dose of 3-MC. The ultrastructural investigations showed that 3-MC treatment caused nucleolar hypertrophy and accumulation of lipid inclusions in the nucleoplasm.

Animals↗
PubMed1979

Perichromatin granules in the liver nuclei after isolation of hnRNP (informofer) particles.

The influence of the extraction of hnRNP (informofer) particles on the ultrastructural appearance of the perichromatin granules was studied. The extraction of hnRNP particles was carried out by SAMARINA's procedure from the rat liver nuclear fraction. The extraction did not change the numbers and the general ultrastructural features of perichromatin granules. It is therefore unlikely that the perichromatin granules are the morphological representatives of storaged or transported hnRNA.

Animals↗
PubMed1976

Nuclear and polyribosomal ribonucleoprotein particles containing poly (A) in rat liver cells.

Poly(A) containing ribonucleoprotein particles were prepared from rat liver nuclei and polyribosomes. The particles have sedimentation coefficients of 14 S and 9 S, respectively. In CS2SO4 density gradients the particles banded at densities of 1.28-1.29 g cm-3. Both nuclear and polyribosomal poly(A)-RNP contain in addition to some minor polypeptides, two main polypeptides having molecular weights of 63 000 and 90 000 dalton, respectively indistinguishable from each other according to their electrophoretic mobilities.

Animals↗
PubMed1975

Electron microscopic observations on the poly(A)-RNP component of the pre-mRNA containing nuclear complexes.

The nuclear ribonucleoprotein particles containing polyadenylic acid were prepared from rat liver nuclear extract by treatment with RNase I. The sedimentation coefficient of the particles was approximately 14 S. These particles represent a component of the pre-mRNA containing ribonucleoprotein complexes of the nucleus. The submicroscopic morphology of the particles was examined in preparations pretreated by platinum-palladium shadowing and by various negative staining methods as well as in ultrathin sections. The 14 S particles are globular structures, 120-140 A in diameter. The particles are characterized by a strong tendency to aggregation. The results are discussed with respect to mRNA transport.

Animals↗