Methylation of newly synthesized ribonucleic acid by isolated rat liver nuclei. Characterization of the ribonucleic acid synthesized by nuclei from starved animals.
1. Nuclei from rat liver incubated with S-adenosyl[methyl-(14)C]methionine incorporated radioactivity into RNA and into lipid and protein. 2. All of the labelled RNA was extracted from the nuclei with trichloroacetic acid at 90 degrees C. 3. The [(14)C]methyl-group incorporation into the hot-trichloroacetic acid extract was 30% inhibited by the addition of actinomycin D (100mug/mg of DNA) or by the omission of CTP, GTP and UTP. 4. Assuming that the main substrate for this triphosphate-dependent methylation was newly synthesized precursor rRNA containing one methyl group/30 uridylate residues, it was calculated that approx. 60% of the [(14)C]UMP incorporated under similar conditions represented precursor rRNA synthesis. 5. In agreement with this, low concentrations of actinomycin D (approx. 1mug/mg of DNA) sufficient to abolish the triphosphate-dependent incorporation of [(14)C]methyl group inhibited 68% of the [(14)C]UMP incorporation. 6. The incorporation of [(14)C]UMP by nuclei from starved animals decreased progressively with increasing periods of starvation, whereas the triphosphate-dependent [(14)C]methyl-group incorporation was not further decreased after 1 day of starvation. 7. This suggests that precursor rRNA synthesis decreased within 1 day whereas other species of RNA were affected only after longer periods of starvation.
D000818:Animals; D002247:Carbon Isotopes; D002467:Cell Nucleus / Q000378:metabolism*; D003597:Cytosine Nucleotides / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D008715:Methionine / Q000378:metabolism; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis*; D012335:RNA, Ribosomal / Q000096:biosynthesis; D051381:Rats; D013217:Starvation / Q000378:metabolism*; D014238:Trichloroacetic Acid; D014500:Uracil Nucleotides / Q000378:metabolism
D002247:Carbon Isotopes; D003597:Cytosine Nucleotides; D006150:Guanine Nucleotides; D012335:RNA, Ribosomal; D014500:Uracil Nucleotides; D003609:Dactinomycin; D014238:Trichloroacetic Acid; D012313:RNA; D008715:Methionine; D008780:Methyltransferases