Mutations in the anticodon of tRNAGlu (UUC) were isolated or constructed and characterized for their ability to suppress cognate nonsense or missense mutations in vivo. The C36-to-A36 transversion mutation was isolated as an ochre and an amber suppressor, while the G36 transversion was selected as a CAG missense suppressor. tRNAGlu suppressors of an AAG missense mutation could not be isolated, and a U36 transition mutation introduced into tRNAGlu in vitro conferred no suppressor phenotype. Over-expression of glutamyl-tRNA synthetase did not increase the activity of the U36 mutant tRNAGlu, suggesting a defect at the level of translation rather than at the level of synthetase recognition.
