Polyadenylated RNAs as error sources in ribosomal RNA turnover analyses.

An approach to ribosomal RNA turnover studies in which cytoplasmic RNA was extracted and subsequently fractionated to isolate ribosomal RNA is reported. The presumption that the pool of 28S and 18S RNAs represented ribosomal RNA, exclusively, proved false and led to erroneous results of ribosomal RNA turnover. Polyadenylated RNAs exhibited a heterogeneous size distribution and, although constituting only 3% (w/w) of the cytoplasmic RNA extract, accounted for fully 10% of radioactivity of the presumptive ribosomal RNA pool. Profiles from the radioactivity data suggested that the discrepant results were due to these polyadenylated RNAs. An additional analytical procedure, an oligo (dT) cellulose column chromatography of the RNA extract prior to the sucrose density gradient fractionation step, performed as described in this paper, proved an effective remedy for this error.