Direction of transcription of the regulatory gene araC in Escherichia coli B-r.

The protein product of the regulatory gene araC can be synthesized in a cell-free, protein-synthesizing system programmed with a lambdaparaC(+)B DNA template. Hybrid, renatured phage DNA molecules prepared with DNA from phages lambdaparaC(+)B and lambdaparaC3B (araC3 is a nonsense mutation) were used to program the cell-free synthesis of the araC protein. The findings observed lead to the conclusion that the codogenic strand of the araC gene is on the light strand of the phage DNA. The araB gene is on the heavy strand, as determined by DNA.RNA hybridization. Thus, with regard to the standard E. coli map, araC is transcribed in a clockwise direction, whereas transcription of the araBAD operon has a counterclockwise orientation. The technique described should allow one to determine the direction of transcription of any gene that can be incorporated into the genome of a specialized transducing phage.