Shadow promoters in the F plasmid transfer operon

The in vivo transcription start site for PYZ, the promoter of the F plasmid transfer operon, has been located. When transcription start sites for PYZ are deleted, two additional shadow promoters, upstream of PYZ, are activated in vivo. The shadow promoters correspond to those previously identified by in vitro run-off transcription experiments. The activated shadow promoters are stimulated by TraJ protein, a positive regulator of the transfer operon.