FIG. 1.

Anaerobic stability and O₂ regulation of stability of the chromosomal nifHDKTY mRNA in the wild-type background and the pUX40 nifHDKTY mRNA in the ΔnifDK background. Representative Northern blots of RNA isolated after rifampin addition from chromosomal (UN) (panel 1) and ΔnifDK/pUX40 (UN5442) (panel 2) anaerobic cells derepressed for nif expression and from chromosomal (panel 3) and ΔnifDK/pUX40 (panel 4) cells treated with O₂. Sampling times are indicated in minutes above the lanes. The time of O₂ addition relative to sampling is indicated with a downward arrow above the indicated sampling times. A nifTY-specific probe was used in panels 1 and 2, and a nifKTY-specific probe was used in panels 3 and 4. Arrows a indicate nifHDKTY mRNA, and arrows b indicate nifHDK mRNA.