Studies of the thermal conversion of 28 s RNA of Galleria mellonella (L.) to an 18 s product

Abstract

The 28 s RNA from the silk gland of wax moth is converted to an 18 s component by heat treatment, or urea. The results suggest that the conversion consists of a dissociation of the molecule due to the presence of break(s) in primary structure rather than a change in conformation. It is likely that the break(s) is introduced into the polynucleotide chain during or after the process of 28 s ribosomal RNA formation from its precursor since a precursor is apparently resistant to the heat treatment. It appears that a single molecule of 28 s rRNA gives rise to two molecules of the 18 s product. The 18 s product and native 18 s RNA showed an identical mobility on polyacrylamide gel electrophoresis, whereas the former appeared to be a little heavier by sucrose gradient centrifugation analysis. The nucleotide composition of the 18 s product was nearly identical to that of the 28 s rRNA and was significantly higher in G + C content than that of 18 s rRNA. From sedimentation velocity analyses, 27.2 s, 17.7 s, and 18.2 s were obtained for the S 0 20,w values of so-called 28 s, 18 s RNA's and the 18 s thermal product, respectively.