Missense Suppression Due to a Genetically Altered tRNA

Several missense mutations affecting the tryp-tophan synthetase A-protein can be suppressed. (See Yanofsky, Helinski, and Maling, 1961). In particular, mutations at sites specifying different glyeine residues in the A-protein have been ex-tensively studied (Fig. 1). The A23 and A36, (hereafter referred to as A36) and A46 mutations result in replacement of the glycine in peptide CP-2 by arginine and glutamie acid, respectively (Helinski and Yanofsky, 1962; Henning and Yanofsky, 1962), while the A78 and A58 mutations lead to substitution of cysteine and aspartic acid, respectively, for the glycine residue in peptide TP-6 (Guest and Yanofsky, 1965). Mutations leading to suppression of A36 (su+6), A78 (SU~s),