Tryptophanyl-tRNA synthetase, gene

The 37-kDa 334-residue subunits of the dimeric type I tryptophanyl-tRNA synthetase238 are the smallest known the largest bacterial synthetase is an alanine-specific type II tetramer with 95-kDa 875-residue subunits.239 Gene deletions show that a much smaller core, comparable in size to that of the tryptophanyl-tRNA synthetase, is needed for amino acid activation. The synthetases share little sequence homology except for a short 11-residue part of the adenylate binding site near the N terminus.240 241 Some of the synthetases contain bound zinc ions.225,242... 

Rubin et al.346 reported the cloning and characterization of a cDNA, representing a gene where expression is upregulated in INF-treated cells. This gene encodes a protein that has sequence homology with and the biological activity of a tryptophanyl-tRNA synthetase. 

There have not been any reports of strains resistant to tryptophan analogs as a result of mutant tryptophanyl-tRNA synthetase. However, three laboratories have independently isolated strains of E. coli with partial tryptophan auxotrophies (bradytrophs) as a result of mutations in what appears to be the structural gene, trpS, for tryptophanyl-tRNA synthetase [187,188,214,215]. The partial auxotrophy was overcome by either tryptophan or indole supplementation but not by anthranilate. 

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