Suppression of nonsense mutations in cell culture and mice by multimerizedsuppressor tRNA genes

We demonstrate here the first experimental suppression of a premature termi nation codon in vivo by using an ochre suppressor tRNA acting in an intact mouse. Multicopy tRNA expression plasmids were directly injected into skele tal muscle and into the hearts of transgenic mice carrying a reporter gene with an ochre mutation. A strategy far modulation of suppressor efficiency, applicable to diverse systems and based on tandem multimerization of the t RNA gene, is developed. The product of suppression (chloramphenicol acetylt ransferase) accumulates linearly with increases in suppressor tRNA concentr ation to the point where the ochre-suppressing tRNA(Ser) is in four- to fiv efold excess over the endogenous tRNA(Ser). The subsequent sup presser acti vity plateau seems to be attributable to accumulation of unmodified tRNAs. These results define many salient variables for suppression in vivo, for ex ample, for tRNA suppression employed as gene therapy for nonsense defects.