FIG. 4.

Effect of NtcA and 2-OG on transcription from promoters of the hetC, nrrA, and devB genes. In vitro runoff transcription assays were performed with DNA fragments of the hetC (A), nrrA (B), or devB (C) genomic region in the presence or absence of NtcA and 2-OG as indicated. NtcA (130 nM [A], 170 nM [B], and 41 or 100 nM [C]), supplemented with 2-OG (0.6 mM) when indicated, was incubated with the DNA fragment before the addition of RNAP (27 nM plus 88 nM SigA [A and B] and 29 nM plus 96 nM SigA [C]; see Materials and Methods for details). Where indicated with *, RNAP was first added to the DNA preparation and, after incubation, supplemented with NtcA and 2-OG. Arrowheads indicate full transcripts encompassing positions from the corresponding tsp to the end of the Anabaena fragment used. Size markers (in nucleotides) are also indicated.