Characterization of devH, a gene encoding a putative DNA binding protein required for heterocyst function in Anabaena sp strain PCC 7120

The devH gene was identified in a screen for Anabaena sp. strain PCC 7120 s equences whose transcripts increase in abundance during a heterocyst develo pment time course. The product of devH contains a helix-turn-helix moth sim ilar to the DEM binding domain of members of the cyclic AMP receptor protei n family, and the protein is most closely related to the cyanobacterial tra nscriptional activator NtcA. devH transcripts are barely detectable in vege tative cells and are induced approximately fivefold after nitrogen starvati on. This induction is absent in the two developmental mutants hetR and ntCA . The gene is expressed as monocistronic transcripts with multiple 5' termi ni, and the similar to 500-bp region 5' to devH was shown to have promoter activity in vivo. The devH gene aas insertionally inactivated by the integr ation of plasmid sequences within the open reading frame. Nitrogen starvati on 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 ac etylene aerobically.