FIG. 3.

Ca²⁺-induced DNA cleavage by DNA gyrase. CaCl₂ was added to reaction mixtures containing WT or mutant gyrases (final concentrations, 25 nM) and relaxed pBR322 DNA. The amount (shown as a percentage) of cleaved product (linear pBR322) was quantified. Results are averages from three separate experiments and are normalized such that the intensity of the linear band in the WT cleavage reaction is 100% at 2 mM CaCl₂. Symbols: ○, WT; ●, Ala⁸³; □, Ala⁸⁷; ■, Ala⁸³ Ala⁸⁷.