Initiator-specific binding activity in T. vaginalis nuclear extracts. A 37-bp probe, corresponding to positions −15 to +15 of the αSCS Inr region, was used in mobility shift assays with 20 μg of T. vaginalis crude nuclear extract. The αSCS Inr is a tandem Inr (underlined) that is known to contain two transcription initiation sites (indicated by the arrows) (17). Competition assays were performed with a 100× molar ratio of unlabeled wild-type and mutant αSCS Inr probes. Lane 1, no extract; lane 2, with extract; lane 3, competition with wild-type αSCS Inr; lane 4, competition with Inr13; lane 5, competition with Inr3. DNA sequences of the three probes are shown with the mutations in the Inr13 and Inr3 probes in boldface.