High-resolution proton magnetic resonance study of the secondary structure of the 3'-terminal 49-nucleotide fragment of 16S rRNA from Escherichia coli.

The 3' terminus of 16S rRNA has been implicated in the recognition of mRNA's by the ribosome. A fragment containing the 3'-terminal 49 nucleotides cleaved from the rRNA by cloacin DF13 was isolated in a pure form. The secondary structure of this fragment has been studied by measuring the high-resolution proton magnetic resonance spectra. The resonances observed at low field can be assigned to hydrogen-bonded iminoprotons of base-pairs present in the fragment. From the data we conclude that the rRNA fragment, under the conditions used, exists as a hairpin consisting of eight intramolecular base-pairs, the 3'-terminal dodecanucleotide being unpaired. The implications of these findings with respect to the function of the ribosomal protein S1 are discussed.