FIG. 2.

DNA supercoiling in the presence of NaCl. Increasing amounts of NaCl were added to standard supercoiling reaction mixtures containing WT or mutant gyrases. Lanes 1, DNA substrate only; 2, no added NaCl; 3, 100 mM NaCl; 4, 150 mM NaCl; 5, 200 mM NaCl; 6, 250 mM NaCl; 7, 300 mM NaCl. WT and mutant GyrA subunits were added at a concentration of 11 nM. Differences in the supercoiling activities of mutants were accounted for by varying incubation times: for WT, 3 min; for Ala⁸³, 2.5 min; for Ala⁸⁷, 7 min; and for Ala⁸³ Ala⁸⁷, 10 min.