Sequence verification of mutant codon assignments in trpA of Escherichia coli

Over the past 30 years, a variety of mutations have been characterized in trpA, the gene for the alpha-subunit of tryptophan synthetase in Escherichia coli. On the basis of amino acid sequence analyses, reversion studies, or suppressibility by codon-specific translational suppressors, base substitutions were deduced and codons assigned for each mutation. In the present study, three of the trpA mutants obtained over 25 years ago and a series of codon position 234 trpA mutants isolated more recently by specific selection methods have been cloned and characterized by DNA sequence analysis. Our results establish the reliability of the mutant codon assignments, confirm the validity of the selection and detection procedures used to obtain missense and nonsense mutations in trpA, and demonstrate that the trpA sequence has been stably maintained throughout 30 years of laboratory culturing and mutagenic treatments.