Determination of the transcription direction of the exuT gene in Escherichia coli K-12: divergent transcription of the exuT-uxaCA operons.

The exuT gene of Escherichia coli, coding for the hexuronate transport system, was fused to lac genes by the use of Mu d(Apr lac) insertions (M. J. Casadaban and S. Cohen, Proc. Natl. Acad. Sci. U.S.A. 76:4530-4533, 1979). The method of chromosome mobilization with F' lac::Mu episomes (J. B. Zeldis, A. I. Bukhari, and D. Zipser, Virology 55:289-294, 1974) made it possible to determine the transcription direction of the exuT gene from the orientation of the Mu d(Apr lac) insertion in the fusion strains. Our results for a exuT-lac fusion strain suggest that the direction of transcription of other single gene operon exuT is clockwise on the standard E. coli map and confirm that the direction of transcription of uxaC is counterclockwise. The two close operons exuT and uxaCA are thus transcribed in opposite directions.