Transport and utilization of sugar phosphates in Escherichia coli depend on the transport protein encoded by the uhpT gene. Transmembrane induction of uhpT expression by external glucose 6-phosphate is positively regulated by the promoter-specific activator protein UhpA and the global regulator catabolite gene activator protein (CAP). Activation by UhpA requires a promoter element centered at -64 bp, relative to the start of transcription, and activation by CAP requires a DNA site centered at position -103.5. This DNA site binds the cyclic AMP-CAP complex in vitro, and its deletion from the promoter reduces transcription activity to 7 to 9% of the wild-type level. Ten uhpT promoter derivatives with altered spacing between the DNA site for CAP and the remainder of the promoter were constructed. Their transcription activities indicated that the action of CAP at this promoter is dependent on proper helical phasing of promoter elements, with CAP binding on the same face of the helix as RNA polymerase does. Five CAP mutants defective in transcription activation at class I and class II CAP-dependent promoters but not defective in DNA binding or DNA bending (positive control mutants) were tested for the ability to activate transcription. These CAPpc mutants exhibited little or no defect in transcription activation at uhpT, indicating that CAP action at uhpTp involves a different mechanism than that which is used for its action at other classes of CAP-dependent promoters.