Characterization of devH , a Gene Encoding a Putative DNA Binding Protein Required for Heterocyst Function in Anabaena sp. Strain PCC 7120

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Abstract
The devH gene was identified in a screen for Anabaena sp. strain PCC 7120 sequences whose transcripts increase in abundance during a heterocyst development time course. The product of devH contains a helix-turn-helix motif similar to the DNA binding domain of members of the cyclic AMP receptor protein family, and the protein is most closely related to the cyanobacterial transcriptional activator NtcA. devH transcripts are barely detectable in vegetative cells and are induced approximately fivefold after nitrogen starvation. This induction is absent in the two developmental mutants hetR and ntcA . The gene is expressed as monocistronic transcripts with multiple 5′ termini, and the ∼500-bp region 5′ to devH was shown to have promoter activity in vivo. The devH gene was insertionally inactivated by the integration of plasmid sequences within the open reading frame. Nitrogen starvation of the devH mutant induces heterocysts of wild-type morphology, but the mutant is inviable in the absence of fixed nitrogen and unable to reduce acetylene aerobically.