Optical Rotatory Dispersion and Secondary Structure of Ribonucleic Acid in Mammalian Ribosomes

Abstract

MACROMOLECULAR single-stranded RNA from viruses and ribosomes is now generally thought to contain short double-helical regions¹ formed when the polynucleotide chain bends back on itself. The existence of such regions was largely inferred from the changes in ultra-violet absorption which occurred on heating solutions of macromolecular RNA. What, however, is the relation between the configuration of macromolecular ribosomal RNA in solution and in the original ribosome? Yeast ribosomes have been reported to have an optical density equal to the sum of the optical densities of the separated RNA and protein². Other evidence has been obtained by measuring the changes in ultra-violet absorption of ribosomes when these are heated (and from X-ray diffraction investigations³). The increases in ultra-violet absorption which were observed were the same⁴ or about two-thirds^1a of those of the isolated ribosomal RNA. Measurement of increases in ultra-violet absorption on heating mixed systems of nucleic acids and proteins is not always very satisfactory on account of turbidity changes (for example, ref. 5) and independent evidence has therefore been sought by measuring the optical rotatory dispersion curves of intact ribosomes and of the RNA and protein isolated from them.