Leftward transcription in the Escherichia coli bio operon does not require products of the rightward transcript

The amount of leftward transcription in the Escherichia coli bio operon, as measured by hybridization and by beta-galactosidase assays in lac-bio fusion strains, was determined in bacteria lysogenic for lambda bio phage carrying different amounts of DNA corresponding to rightward message, and in bacteria with polar or nonpolar bioB mutations. The positions of the bioB endpoints in relation to the pB promoter were determined by electron microscopy of heteroduplexes. Normal rates of leftward transcription were found in all cases, except that the shortest lambda bio (lambda bio showed a 2- to 3-fold increase in leftward transcription, which was not abolished by the presence of a wild-type bio operon in trans. These results indicate that no product of the rightward transcript is needed to turn on leftward transcription.