The low molecular weight ribosomal RNA species, 5.8S rRNA, is found in the larger ribosomal subunit of eukaryotic cells; it occurs in equimolar ratios to the 28S rRNA molecule and is hydrogen-bonded to that component. The nucleotide sequences of 5.8S rRNA from several organisms have been determined and a secondary structure proposed, based on maximised base pairing. The aim of this work has been to investigate the conformation of HeLa cell 5.8S rRNA. The approach to this investigation involved the use of the technique of chemical modification. The assumption behind such an approach is that a base residue which is not modified by a reagent specific for that base is inaccessible. Bases involved in double helical stems of the molecule are unreactive and the reaction will be diminished if a base is involved in maintaining the tertiary structure through stacking or base pairing. Only bases not involved in such interactions will be significantly modified by a reagent specific for that base. The correlation between the three dimensional structure of yeast tRNAPhe and the results obtained from chemical modification studies suggest that such studies carried out on 5.8S rRNA should provide useful data concerning the conformation. Two modifying reagents, were used in this study; sodium bisulphite, which reacts specifically with non-hydrogen bonded cytidine residues, converting them to uridine, and carbodiimide, which under the conditions used has high specificity for non-hydrogen bonded uridine residues. When these techniques are coupled with 'fingerprinting' procedures it is possible to investigate the structure of 5.8S rRNA. When these studies were carried out on isolated 5.8S rRNA at 2
