Amino acid sequences of fifty residues from the amino termini of the tryptophan synthetase chains of several enterobacteria.

The sequences of the first 50 residues of the tryptophan synthetase o( chains of Shigella dysenteriae, Salmonella typhimurium, and Aerobacter aerogenes were determined and compared with the corresponding sequences of Escherichia coli and Pseudomonas putida. On the basis of observed amino acid residue differences, and inferred nucleotide differences in the respective genes, similarity to the E. coli sequence decreases for the following species in the order: S. dysenteriae > (S. typhimurium, A. aerogenes) > P. putida. This order is examined in relation to the results of investigations employing other means of assessing genetic homology.