FIG. 5.

Expression and processing of fis mRNAs after a temperature downshift. Cells were grown at 37°C to log phase as indicated in Materials and Methods before being transferred to 28°C. After 20 min, rifampin at 250 μg/ml (final concentration) was added to the cells, and the RNA was extracted at the indicated time (for time zero the RNA was extracted immediately before the addition of rifampin). Portions (10 μg) of the RNA samples were used for Northern blot analysis with an oligonucleotide probe hybridizing to fis as described in Materials and Methods. The strains used were MA249 [gyrB(Ts)], MA251 [gyrB(Ts) topA], and IB34 [gyrB(Ts) topA/pSK760]. + RNase HI indicates that RNase HI was overproduced (pSK760).