The 3′ terminus of the large ribosomal subunit (“17S”) RNA from hamster mitochondria is ragged and oligoadenylated

Abstract

The 3′-terminal sequence of the large ribosomal subunit (“17S”) RNA of hamster mitochondria has been examined by means of oligonucleotide finger-print analysis of 3′ end-labeled samples. Patterns from partial acid or alkaline hydrolysates indicated marked heterogeneity and suggested an array of termini that included GGUUA OH, A nA OH and A nG OH (where n is about 10). Patterns from samples subjected to exhaustive digestion with ribonucleases T 1 plus A, or with each separately, confirmed these inferences, and strikingly demonstrated the existence of oligoadenylated families of 3′-terminal sequences. Under the assumption that the oligoadenylate was added posttranscriptionally, these results indicated that the 3′-terminal transcribed moieties consist of variants of YAGGUU OH. Counting from the last U, we inferred that many such sequences end at U1 and G4, while smaller numbers end at G3 and A5; and that major sites of oligoadenylation occur at U1 and G4, and a minor site occurs at A5. This novel combination of imprecise termination of transcription or “sizing” of transcripts, and variable addition of adenylate residues, is discussed with regard to the mechanism of expression of the mammalian mitochondrial ribosomal RNA genes.