Fig. 4. (A) Denaturing PAGE of the 5′-end labeled template used in these studies. Lane 1: DNase I-treated DNA alone. Lane 2: DNase I-treated DNA with T7RNAP EC halted at +19. Lane 3: DNase I-treated DNA with T7RNAP halted at +15. Lane 4: DNase I-treated DNA with T7RNAP paused at the class II site. Lane 5: DNA alone (no DNase I). (B) Superimposed scans of lanes 1 (black) and 3 (red) from (A). Horizontal line indicates a region of >80% protection. (C) Superimposed scans of lanes 1 (black) and 2 (green) from (A). Horizontal line indicates a region of >80% protection. (D) Superimposed scans of lanes 1 (black) and 4 (blue) from (A). Horizontal line indicates region of >50% protection. Arrows in B–D indicate positions of enhanced DNase I sensitivity.