Genetic fusions that help define a transcription termination region in Escherichia coli.

‘IIN trpA gene product was analyzed from a class of strains of Escherichia coli I112 in which the lac operon has been fused by deletion t,o the trp operon. These are strains that have retained the ability to synthesize tryptophan. Two of these strains are shown to make a wild-type trpA product ; these strains retain intact all structural genes of the trp operon. It is proposed that the lac operon in t,hese strains is fused to a region of the trp operon between trpA, the last gene in the operon, and the region where trp messenger RNA synthesis terminates. The region where trp messenger RNA synthesis terminates thus is distinct from the trp structural genes.