Effect of sequence mutations on the higher order structure of the yeast 5 S rRNA

Mutant yeast ribosomal 5 S RNAs were probed by enzymatic cleavage and chemical reactivity to define further the higher order structure. Mutations that destabilized helix IV resulted in an altered tertiary structure in which a reduced reactivity to ethylnitrosourea at U90 and G91 could be correlated with greater enzymatic and Fe(II)-EDTA cleavages in helices II and V. The results provide direct evidence for, and a further definition of, a structural juxtaposition between helix II and the end of helix IV and indicate that, in contrast to earlier suggestions, the remaining tertiary structure is sufficiently stable to prevent "pseudoknot-like" interactions between helices III and IV. The data are fully consistent with the "lollipop" model of the tertiary structure.