18S rRNA Degradation is Not Accompanied by Altered rRNA Transport at Early TimesFollowing Irradiation of HeLa Cells

摘要

In recent investigations on the effects of radiation on rRNA processing in HeLaS3 cells, we pulse-labeled the cells with uridine immediately prior to irradiation. The 45 S rRNA precursor, which undergoes nuclear processing to form one each of its major daughter species, 28S and 18S rRNA, was separated from the daughter species by gel electrophoresis and the radiolabel in each species determined at various times after irradiation. By pulse-labeling the cells prior to irradiation, superimposed effects caused by radiation-induced alterations of rRNA transcription and Refs. therein were minimized, permitting selective analysis of the processing of that fraction of 45S precursor that had been synthesized (radiolabeled) predominantly prior to irradiation. We now report more detailed studies on 45S rRNA processing within the first 2 h following irradiation in which we have found a maximum 28 S:18 S ratio of 2:1 that is observed about 1 h following irradiation of 5 or 10 Gy.