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Aminoglycosides such as gentamicin，streptomycin，kanamycin and tobramycin are clinically important drugs. The use of these drugs can frequently lead to irreversible hearing loss. Aminoglycoside ototoxicity accounts for a significant portion of deafiness. In familial cases of ototoxic deafness，the aminoglycoside hypersensitivity is often matemaUy transmitted，suggesting that the mutation(s)in mitochondrial DNA is the molecular basis of this disorder. Mutational analysis has led to the identification of several ototoxic mutations in mitochondrial 12S rRNA. In particular，the A1555G and C1494T mutations account for significant cases ofaminoglycoside ototoxicity. The A1555G or C 1494T mutation creates the binding sites of the highly conserved Asiteof 12S rRNA and make the secondary structure of this RNA more closely resemble the corresponding region of bacterial 16S rRNA. Thus，these mutations facilitate the binding of aminoglycosides，thereby accounting for the fact that the exposure to aminoglycosides can induce or worsen hearing loss in individuals carrying these mutations.Therefore，these data