Fig. 2.

The R223W mutation in HetR does not inhibit patS expression upon nitrogen step-down. The AMC1287 merodiploid strain bearing pAM1951, which carries a partial patS ORF followed by gfp as a transcriptional reporter (A, C, and E), or pAM1830, which carries a complete patS gene followed by gfp as a transcriptional reporter (B, D, and F). Images were taken in visible light (A and B) and with fluorescein isothiocyanate-specific illumination (484 ± 8 nm) with (E and F) and without (C and D) GFP-specific emission (518 ± 13 nm) filter sets to cut out red chlorophyll fluorescence from vegetative cells. GFP fluorescence is confined to developing and mature heterocysts.