FIG. 1.
HgdD is up-regulated in proheterocysts upon nitrogen step-down. (A) RNA was isolated from NH4+-grown cells (lane 1) and from cells that had been starved for combined nitrogen for 6, 9, or 12 h (lanes 2 to 4). Samples contained 30 μg RNA. The blots were successively hybridized with 32P-labeled probes for hgdD (upper panel) and rnpB (lower panel), which were used as loading and transfer controls, respectively. The sizes of RNA standards are indicated on the left. (B) N-terminal HgdD-GFP translational fusion in strain NME-alr2887-GFP as visualized by confocal microscopy. The cyanobacterial autofluorescence (AUF.), the GFP fluorescence (GFP), the overlay of the two signals (Overl.), and a bright-field image (BFI) of the NME-alr2887-GFP strain 16 h after nitrogen step-down are shown.