[Turnover of nuclear RNA. III. Detection and characterization of superstable molecules]

In prolonged experiments in which rats were injected with 14C-orotic acid for 7-10 days with subsequent measurements (during 1-2 months) of the label in various rat liver RNA fractions and in the acid-soluble pool, a superstable nuclear RNA fraction was found (T1/2-4.2 days in quiescent rat liver and 4.3 days in regenerating rat liver). A small fraction of this RNA (5-10% of total) is polyadenylated and heterogeneously distributed when electrophoresed in 1% agarose under partially denaturing conditions. Using the conveyer model of synthesis and processing of nuclear RNA advanced earlier the spectrum of turnover rates of superstable transcripts was determined. The data obtained are discussed in light of the hypothesis on posttranscriptional regulation of gene expression.