DNA BENDING BY THE TRPI PROTEIN OF PSEUDOMONAS-AERUGINOSA

TrpI protein, the activator bf transcription of the trpBA operon of fl uorescent pseudomonads, bends the DNA when it forms either df two well characterized complexes with the trpBA regulatory region, In complex 1, with TrpI bound only to its strong binding site (site I), the calcu lated bending angle is 65 to 67 degrees and the center of bending is i n the middle of site I. In complex 2, which is required for activation of the trpBA promoter, with TrpI bound both to site I and to the weak er site ii, the bending angle is increased to 89 to 90 degrees and the tenter of bending is at the site I-site II boundary. Indoleglycerol p hosphate (InGP), which strongly stimulates formation of complex 2 and is required for activation, does not affect the bending angle of eithe r complex. However, a mutation (-10C/11C) shown previously to affect a ctivation has a small but detectable effect on bending, reducing the c alculated bending angle to 83 to 86 degrees. These results suggest a w ay that DNA bending and InGP may be important for activation.