FIG. 2.

Northern blot analysis of the expression of the arsC and arsI genes. Total RNA was isolated from mid-log-phase Synechocystis cells grown in BG11C medium and exposed for 1 h either to 1 mM sodium arsenite [As(III)] or to 10 mM sodium arsenate [As(V)]. Control cells were not exposed to added compounds. Fifteen micrograms of total RNA was denatured, separated by electrophoresis on a 1% agarose gel, blotted, and hybridized with probes for arsC and arsI. The filters were stripped and rehybridized with an rnpB gene probe as a control (see Materials and Methods).