Modulation of Escherichia coli tryptophan (trp) attenuation by the UGA readthrough process

We constructed plasmid pA trp46 in which lacZ gene expression is regulated by the attenuator of the Escherichia coli tryptophan (trp) operon. The attenuation of trp, which occurs in the presence of an excess of tryptophan, is reflected by a decrease in the expression of the lacZ gene of pA trp46 in a trpR^- strain. Experiments with pA trp46 further support our previous results (Engelberg-Kulka et al. 1982b) that suppression of a UGA termination codon by normal charged tRNA^Trp, a process called UGA readthrough, is a necessary mechanism in trp attenuation. Our experiments also suggest that plasmid pA trp46 is useful for studies of other aspects of trp attenuation.