Aminoglycoside antibiotics that bind to the ribosomal A site cause misreading of the genetic code and inhibit translocation. The clinically important aminoglycoside, gentamicin C, is a mixture of three components. Binding of each gentamicin component to the ribosome and to a model RNA oligonucleotide was studied biochemically and the structure of the RNA complexed to gentamicin C1a was solved using magnetic resonance nuclear spectroscopy. Gentamicin C1a binds in the major groove of the RNA. Rings I and II of gentamicin direct specific RNA‐drug interactions. Ring III of gentamicin, which distinguishes this subclass of aminoglycosides, also directs specific RNA interactions with conserved base pairs. The structure leads to a general model for specific ribosome recognition by aminoglycoside antibiotics and a possible mechanism for translational inhibition and miscoding. This study provides a structural rationale for chemical synthesis of novel aminoglycosides.

Translational fidelity is established by ribosomal recognition of the codon-anticodon interaction within the aminoacyl–transfer RNA (tRNA) site (A site) of the ribosome. Experiments are presented that reveal possible contacts between 16 S ribosomal RNA and the codon-anticodon complex. N1 methylation of adenine at position 1492 (A1492) and A1493 interfered with A-site tRNA binding. Mutation of A1492 and A1493 to guanine or cytosine also impaired A-site tRNA binding. The deleterious effects of A1492G or A1493G (or both) mutations were compensated by 2′fluorine substitutions in the mRNA codon. The results suggest that the ribosome recognizes the codon-anticodon complex by adenine contacts to the messenger RNA backbone and provide a mechanism for molecular discrimination of correct versus incorrect codon-anticodon pairs.

The three-dimensional structure of a short DNA fragment, d(GCGAAGC) exhibiting an extraordinarily stable hairpin structure was determined by nuclear magnetic resonance spectroscopy. Two possible models were obtained by molecular modelling using distance and torsion constraints. Only one of these two models Is the correct structure, which can clearly explain all the 1H chemical shifts. d(GCGAAGC) Is folded back on Itself between A4 and As, and all the sugars In the fragment adopt the C2'-endo conformation. This compact molecule Is stabilized by regular extensive base-stacking Interaction within each B-form helical strand of G1C2G3A4 and AgGeCy, and by two G-C and one G3-A5 base pairs. The molecule is hard to differentiate into stem and loop regions, so that we classify It as a turn (halrpln-tum) structure exerted by a single-stranded DNA. This highly stacked structure shows high thermostabillty and strong resistance against nucleases contained in E.coli extracts and in human serum.