Studies on the Secondary Structure of Wheat 5.8 S rRNA: Conformational Changes in the A +U-Rich Stem during Ribosome Assembly

The nucleotide sequence of wheat (Triticum aestivum) 5.8‐S ribosomal RNA has been re‐examined using partial chemical degradation with high‐temperature sequencing gels and oligonucleotide analysis. The results clarify previously ambiguous residues and add two additional nucleotides, G¹²⁷and G¹³⁵, to the sequence. Estimates of the secondary structure suggest that 5.8-S rRNAs of higher plants differ from previous examples in having more open G t C-rich and A +U-rich stems. S₁ ribonuclease digestion was used to probe this secondary structure;the data generally support the ‘burp gun' model proposed for all 5.8-S rRNAs but are also consistent with a more open A +U-rich stem. Diethyl pyrocarbonate reactivity was used to probe the topography of this RNA in wheat ribosomes. The results indicate that the G +C-rich and A +U-rich stems are accessible to chemical modification in the wheat ribosome and suggest that the A +U-rich stem undergoes a significant conformational change when the molecule associates into ribosomes.