title: Ultraviolet-induced inhibition of ribosomal RNA synthesis in yeast strains differing in radiation sensitivities.
abstract: The ultraviolet-induced inhibition of rRNA synthesis has been measured during the first hour after irradiation for stationary yeast cells differing in radiation sensitivity. rRNA was isolated and separated on an agarose-polyacrylamide gel. The wild type and a mutant which is possibly defective in recombinational repair show a sigmoidal inhibition curve, an excision-deficient mutant shows an exponential one. From these curves it is deduced that a pyrimidine dimer acts as a transcription terminating lesion as was shown for bacteria. During the first hour after irradiation the excision repair system decreases the number of transcription terminating lesions by 22% in the wild type and 25% in the mutant defective in recombinational repair. An approximation of the repair efficiency gives a value of 7500-10 000 transcription terminating lesions per cell being removed during the first hour after irradiation by excision. Ultraviolet-induced lesions of this kind can partially be removed by photoreactivation. The inhibition coefficients are the same for 26 S and 18 S rRNA in stationary cells, whereas exponentially growing cells show different inhibition coefficients for 26 S and 18 S rRNA leading to the suggestion that the processing of the ribosomal precursor RNA is different in stationary and exponentially growing cells.
mesh_terms: D002455:Cell Division; D004307:Dose-Response Relationship, Radiation; D005815:Genetic Code; D009154:Mutation; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000378:metabolism / Q000528:radiation effects*; D013045:Species Specificity; D014158:Transcription, Genetic / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D012335:RNA, Ribosomal