Amount of adenine and uracil base pairs in E. coli 23S, 16S and 5S ribosomal RNA.

Abstract

ALTHOUGH ribosomes have been known since the early 1950s, slow progress has been made in determining the structure of their RNA and protein components. Schles-singer1 presented hyperchromicity data which indicated that the configuration of E. coli rRNA in solution was identical with that in ribosomes. Similar results have been obtained by X-ray diffraction2 and optical rotatory dispersion3–5 studies. The idea that rRNA exists as a series of double helical “hair pin” loops, as first proposed by Doty et al.6, has been supported by other laboratories. From model experiments with synthetic polynucleotides7,8. it has been concluded that the degree of base pairing in rRNA is approximately 60 per cent. Based on these data and their own experimental evidence Cotter et al.5 have recently proposed a structural model of yeast ribosomes. Further optical rotatory dispersion studies have shown that E. coli rRNA contains predominantly guanine and cytosine (G—C) base pairs4. Similar results have been reported for rabbit reticulocyte rRNA9. After the isolation, characterization10,11 and base sequence determination12 of 5S rRNA from E. coli., three possible ordered structures have been proposed for this RNA12–14.