Base-pairing in conserved 3' end of 18 S rRNA as determined by psoralen photoreaction and RNase sensitivity.

Wheat and rabbit 18 rRNAs radiolabeled at the 3' end with [5'-32P]pCp were analyzed by polyacrylamide gel electrophoresis after chemical cleavage or partial enzymatic digestion under nondenaturing conditions. rRNA was similarly analyzed after photoreaction with 4'-aminomethyl-4,5',8-trimethylpsoralen and photoreversal of the resulting pyrimidine cross-links. The digestion patterns indicated the presence of a base-paired structure within a conserved 3'-terminal sequence. This structure corresponds to the 3'-proximal hairpin configuration suggested previously for the small subunit rRNAs of Escherichia coli, yeast, rat, and silkworm on the basis of their nucleotide sequences.