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Journal of Bacteriology, November 1999, p. 6664-6669, Vol. 181, No. 21
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The hetC Gene Is a Direct Target of the NtcA Transcriptional Regulator in Cyanobacterial Heterocyst Development

Alicia M. Muro-Pastor, Ana Valladares, Enrique Flores, and Antonia Herrero*

Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Centro de Investigaciones Científicas Isla de la Cartuja, E-41092 Seville, Spain

Received 14 June 1999/Accepted 18 August 1999

The heterocyst is the site of nitrogen fixation in aerobically grown cultures of some filamentous cyanobacteria. Heterocyst development in Anabaena sp. strain PCC 7120 is dependent on the global nitrogen regulator NtcA and requires, among others, the products of the hetR and hetC genes. Expression of hetC, tested by RNA- DNA hybridization, was impaired in an ntcA mutant. A nitrogen-regulated, NtcA-dependent putative transcription start point was localized at nucleotide -571 with respect to the hetC translational start. Sequences upstream from this transcription start point exhibit the structure of the canonical cyanobacterial promoter activated by NtcA, and purified NtcA protein specifically bound to a DNA fragment containing this promoter. Activation of expression of hetC during heterocyst development appears thus to be directly operated by NtcA. NtcA-mediated activation of hetR expression was not impaired in a hetC mutant, indicating that HetC is not an NtcA-dependent element required for hetR induction.

* Corresponding author. Mailing address: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Centro de Investigaciones Científicas Isla de la Cartuja, Avda. Américo Vespucio s/n, E-41092 Seville, Spain. Phone: 34-95-4489522. Fax: 34-95-4460065. E-mail: herrero{at}cica.es.

Journal of Bacteriology, November 1999, p. 6664-6669, Vol. 181, No. 21
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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