Regulation of HetR levels by patA and hetF. Western blot analysis of HetR from cultures 18 h after the removal of combined nitrogen by a polyclonal antibody is shown in panel A. Shown are 100 ng of recombinant HetR used to generate the antibody (lane 1); UHM103, which is a ΔhetR mutant (lane 2); Anabaena sp. strain PCC 7120, which is the wild type (lane 3); UHM101, which is a ΔpatA mutant (lane 4); UHM130, which is a ΔhetF mutant (lane 5); UHM132, which is a ΔhetF ΔpatA mutant (lane 6); UHM103 carrying hetF on replicating plasmid pDR267 (lane 7); Anabaena sp. strain PCC 7120 with pDR267 (lane 8); UHM101 with pDR267 (lane 9); UHM130 with pDR267 (lane 10); and UHM132 with pDR267 (lane 11). Western blot analysis of HetR expressed from the petE promoter on plasmid pPetHetR (5) 18 h after the removal of combined nitrogen and the addition of 3 μM copper and detected by a polyclonal antibody is shown in panel B. Shown are UHM103, which is a ΔhetR mutant with pPetHetR (lane 1); UHM109, which is a ΔhetR ΔpatA mutant with pPetHetR (lane 2); UHM132, which is a ΔhetR ΔhetF mutant with pPetHetR (lane 3); and UHM134, which is a ΔhetR ΔhetF ΔpatA mutant with pPetHetR (lane 4). Western blot analysis of HetRH6 expressed from the nir promoter on plasmid pDR204 18 h after the removal of 5 mM ammonium and addition of 17.6 mM nitrate with an antibody against the polyhistidine epitope tag is shown in panel C. Shown are 100 ng of recombinant HetRH6 (lane 1), UHM103 carrying untagged HetR on plasmid pDR216 (lane 2), UHM103 carrying epitope-tagged HetRH6 on plasmid pDR204 (lane 3), UHM109 carrying pDR204 (lane 4), UHM132 carrying plasmid pDR204 (land 5), and UHM134 carrying plasmid pDR204 (lane 6). Chemiluminescence detection (upper panels) and a Coomassie-stained section of membrane corresponding to an approximate molecular mass of 50 kDa (lower panels) to show equality of protein loading for Western blot analyses are shown in panels A to C. Light (upper panel) and fluorescence (lower panel) microscopy of a mixture of filaments of UHM103, which is a ΔhetR mutant, and UHM132, which is a ΔhetR ΔhetF mutant, both carrying pDR293, a plasmid bearing a hetR-gfp translational fusion expressed from PpetE, 24 h after the removal of combined nitrogen and the addition of 3 μM copper is shown in panel D. Strains are indicated on the left. Carets indicate heterocysts.