title: 18 S ribosomal RNA is degraded during ribosome maturation in irradiated HeLa cells.
abstract: The effects of ionizing radiation (137Cs) on processing of ribosomal RNA (rRNA) were studied by pulse-labeling HeLa S3 cells with [3H]uridine immediately prior to irradiation. The 45 S rRNA precursor, and its two major daughter species, 28 and 18 S rRNA, were separated by gel electrophoresis and the extent of radiolabel incorporation into each was determined at various times after irradiation. This approach permitted kinetic analysis of processing of the 45 S rRNA which had been predominantly synthesized (radiolabeled) prior to irradiation. Since they both derive from the same 45 S pre-rRNA transcript, 28 and 18 S rRNA are produced with a stoichiometry of 1:1, as observed in control cells in the present studies. However, within 1 h following 10 Gy an altered stoichiometry of 28 S:18 S rRNA was apparent, reaching 1.6:1 by 5-7 h following irradiation. This alteration was also observed following the higher dose of 20 Gy, but not following exposures of 5 Gy or less. The 18 S portion of the 45 S pre-rRNA is transcribed prior to the 28 S portion. Consequently, an increase in the 28 S/18 S ratio can only be due to degradation of the 18 S species during or after processing. This alteration may represent a response to radiation-induced growth arrest, by reducing the number of newly synthesized ribosomes that would otherwise be required for cell propagation.
authors.affiliation: Armed Forces Radiobiology Research Institute, Bethesda, Maryland 20814-5145.
authors.forename: J M
authors.initials: JM
authors.lastname: Krolak
authors.forename: D
authors.initials: D
authors.lastname: McClain
authors.forename: S L
authors.initials: SL
authors.lastname: Snyder
authors.forename: P
authors.initials: P
authors.lastname: Fuchs
authors.forename: K W
authors.initials: KW
authors.lastname: Minton
mesh_terms: D002588:Cesium Radioisotopes; D006367:HeLa Cells; D006801:Humans; D012334:RNA, Neoplasm / Q000528:radiation effects; D012335:RNA, Ribosomal / Q000528:radiation effects*; D012337:RNA, Ribosomal, 18S / Q000528:radiation effects*; D012339:RNA, Ribosomal, 28S / Q000528:radiation effects
chemical_list: D002588:Cesium Radioisotopes; D012334:RNA, Neoplasm; D012335:RNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S