The circular dichroism of ribosomal ribonucleic acids

Abstract

The CD (circular dichroism) of Drosophila melanogaster ribosomal[r]RNA (42% G + C) and of G + C-rich fragments (78% G + C) obtained by partial hydrolysis of rabbit L-rRNA (the largest RNA species isolated from the large subribosomal particle) were measured and found to differ substantially. To interpret these spectra a relation between CD of bihelical RNA and % G + C was derived. A frame of reference was established by studying the CD of a range of rRNA species, including S-rRNA (the RNA species isolated from the smaller subribosomal particle) and L-rRNA of Escherichia coli. For the rRNA species studied, 0.60 .+-. 0.05 of residues appear to form bihelical secondary structure. A higher helical content, 0.66 .+-. 0.05, was found for the G + C-rich fragment of L-rRNA. The difference in the CD of rabbit L-rRNA and of D. melanogaster rRNA is attributable to the dependence of CD of the bihelical parts on % G + C. The minimum in CD at 295 nm increases with increasing % G + C. The CD of rRNA was compared with that of the parent subparticle in this region of the spectrum where high precision may be attained.