A novel mutation in the anticodon stem of E. coli tRNA1Tyrsu3+ (G43 to U43) has been characterized. The gene c⊕ding for the mutant tRNA, carried by phage Ø80DHA61.3 a derivative of Ø80psu3+su0 , produces only 20% of mature suppressor tRNA as compared with Ø80psu3. Both the mutant tRNA precursor and mature tRNA have an altered conformation. The precursor tRN+A coded for by Ø80DHA61.3 is processed by RNase P more slowly than the suØ3. pre+cursor and does not form as stable an enzyme-substrate complex as does su3, precursor. Ø80DHA61.3 also +contains a large d-eletion which begins in the spa-cer region between the su, gene and the su3+. gene, extends through the su0. gene and includes most of the repeated region following the tRNA genes.
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