The Effect of a Cytidine‐to‐Uridine Transition on the Stability of Escherichia coli A19 5‐S RNA

Abstract

Several species of 5S rRNA were isolated from E. coli A19. These molecules were separated on the basis of their differing stabilities during electrophoresis on 12% polyacrylamide gels in 7 M urea. This differing stability is shown, in 1 case, to be due to different primary sequence. The sequence of the least stable of these molecules was determined and it differed from the published sequence of E. coli A19 5 S RNA in only 1 residue, i.e., a uridine in place of a cytidine at position 92. The consequent G .cntdot. U base pair, formed in a normally highly stable G .cntdot. C-rich region, is responsible for a drastic reduction in the stability of the molecule. This instability leads to a less constrained, more compact molecule which thus migrates faster in electrophoresis under denaturing conditions. This species of 5 S RNA makes up 30% of the total 5 S RNA in the 50 S ribosomal subunits in this organism. Further structural studies were carried out using S1 nuclease digestion, sodium bisulfite modification and thermal melting analysis. All these methods indicate a 5 S RNA drastically destabilized in parts of its secondary and tertiary structure. The ability of the variant 5 S RNA to recognize and form a complex with its 50 S subunit binding proteins was examined and found to be impaired.