title: Photo-induced protein-RNA cross-linking in mammalian 60-S ribosomal subunits.
abstract: Rat liver 60-S ribosomal subunits were submitted to increasing doses of radiation (253.7 nm), at 4 degrees C and 25 degrees C, as previously reported fro 40-S subunits. The existence of protein-RNA cross-linking was demonstrated by two methods. The first consisted in the separation of protein-RNA complex; the second was indirect, and took into account alteration either in the electrophoretic mobility of cross-linked proteins or the separability of 28-S RNA in a 4 M urea/3 M LiCl buffer. The peptide synthetase activity and the sedimentation characteristics of the particles irradiated at 4 degrees C were well preserved, but at 25 degrees C the large subunits were progressively inactivated and unfolded for doses higher than 2 x 10(18) quanta. The dose-dependent variations of protein cross-linkage determined by two-dimensional gel electrophoresis allowed us to distinguish those proteins which reacted at the lowest doses with a first-order reaction from those which cross-linked to RNA after a subtle modification of the subunit structure. At 25 degrees C, all proteins became low-dose reactive. The curve obtained for 28-S RNA cross-linkage was similar to that of the total protein moiety, while those obtained fro the 5-S and 5.8-S RNA (which were parallel) suggest a lower reactivity of these RNAs. As a general rule, proteins from the large subunits were more reactive to RNA than those from the small subunits. This could indicate differences in the organisation of the two subunits.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D004307:Dose-Response Relationship, Radiation; D008099:Liver / Q000378:metabolism; D009691:Nucleic Acid Denaturation; D011489:Protein Denaturation; D012335:RNA, Ribosomal / Q000378:metabolism / Q000528:radiation effects*; D051381:Rats; D012269:Ribosomal Proteins / Q000378:metabolism / Q000528:radiation effects*; D012270:Ribosomes / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D012335:RNA, Ribosomal; D012269:Ribosomal Proteins