Missense and nonsense suppressors derived from a glycine tRNA by nucleotide insertion and deletion in vivo.

Beginning with a missense suppressor tRNA and a nonsense suppressor tRNA, both in Escherichia coli and each containing an extra nucleotide in the anticodon loop, we generated new suppressors in vivo by spontaneous deletion of specific nucleotides from the anticodon loop. In one experiment, the new suppressor was generated by a double mutational event, base substitution and nucleotide deletion. A novel ochre suppressor is also described. It is very efficient in nonsense suppression but has no ms2i6 modification of the A residue on the 3' side of the anticodon. The results have important implications for tRNA structure-function relationships, tRNA recognition by tRNA-modifying enzymes, mechanisms of deletion mutation, and tRNA evolution.