FIG. 3.

SirA alters the gel mobilities of promoter DNA fragments. Eight promoter DNA fragments (shown below panels) were tested for their abilities to bind purified SirA in a gel mobility shift assay. SirA was phosphorylated by incubation with BarA198 and ATP for 25 min and then was added to promoter DNA labeled with [γ-³²P]ATP. Each reaction was resolved by nondenaturing PAGE, and samples were detected with a PhosphorImager. The micromolar concentration of SirA in each reaction is indicated above each lane. An asterisk indicates that a 30- to 50-fold excess of unlabeled promoter DNA fragment was added to the reaction as a specific competitor. All reactions contained nonspecific competitor DNA [2 μg of poly(dI-dC)] and protein (0.2 μg of BSA).