Fig 3.

The four promoters of the all4725-all4721 operon are constitutively transcribed in a zur mutant. (A) Schematic representation of the all4725-all4721 operon showing the primers used for primer extension in panel B. (B) RNA from WT cells or the zur mutant not treated (−) or treated (+) with 20 μM TPEN for 24 h was subjected to primer extension with the primers indicated at the top. A sequencing reaction mixture generated with the P1 primer is shown at the left for sizing. Arrowheads point to extension products at the expected positions for transcripts initiating at P5, P3, P2, and P1. The bottom panel corresponds to a primer extension control experiment performed with the same RNA preparations and primer ALL4727_2R. (C) Impact of Zur on transcription of P3, P2, and P1 in vitro. A total of 25 fmol linear DNA templates containing the sequences of the P3, P2, and P1 promoters was incubated with 150 nM recombinant Anabaena RNAP, dNTPs, and [α-³²P]CTP in the absence (−) or presence (+) of 5 pmol recombinant Zur protein. The expected position for runoff transcripts is indicated with an arrowhead.