Differential Metabolism of Large and Small Poly(A) Sequences in the Heterogeneous Nuclear RNA of HeLa Cells

Abstract

The heterogeneous RNA of the HeLa cell nucleus contains short internal poly(A) sequences which, in contrast to the longer poly(A) sequences at the 3′ ends, are not found in messenger RNA of the cytoplasm. A distinct origin for each of these homologous sequences is evident when the effects of actinomycin D and 3′-deoxyadenosine on their biosynthesis are compared. The shorter poly(A) appears to be transcribed, while the longer one does not. A kinetic analysis of the metabolism of each type of poly(A) sequence within different size classes of HnRNA after treatment of the cells with 3′-deoxyadenosine reveals distinctive distribution and metabolism of these sequences and also provides insight into mechanisms proposed for the generation of messenger RNA from these large RNA molecules in the nucleus.

Identification of Methylated Nucleosides in Messenger RNA from Novikoff Hepatoma Cells

“…Thus, the peak of N6-methyladenosine radioactivity contains an unknown contribution from 1-methyladenosine. 7-Methylguanosine is also relatively unstable (22) and is converted under our hydrolysis conditions to a product that migrates near the solvent front on high-speed liquid chromatography.…”

“…3971 adenosine residues to the 3'-end (5). Studies on its function are still inconclusive, but several findings can be cited outlining its importance (5)(6)(7). Like methylation in rRNA, adenylation seems to play an essential role in the metabolism of mRNA molecules.…”

The Occurrence and Distribution of Poly(A) Ribonucleic Acid in Soybean

“…There is, however, some evidence for poly(A) synthesis in the cytoplasm (36,40) along with some turnover in the terminal AMP residues (7). In addition to the 3' terminal poly(A) sequence, the poly(A) RNA from at least some species contains a shorter internal sequence (26,34) RNA was extracted and purified as previously described (22). Polyribosomes were prepared as described by Anderson and Key (2).…”

RNA and Protein Synthesis in Herpesvirus-Infected Cells

“…nuclear RNA contains only poly (A)30 indicates that adenylation is not a single step process. Silverstein et al (x976) have suggested that poly (A)30 chains may arise by a transcriptional process similar to that suggested for generation of the short internal poly (A) stretches in HeLa cell Hn RNA (Nakazato, Edmonds & Kopp, 1974) and that further adenylation of virus RNA results from a post transcriptional mechanism.…”