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Journal of Bacteriology, September 2009, p. 5765-5774, Vol. 191, No. 18
0021-9193/09/$08.00+0     doi:10.1128/JB.00616-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

NtcA-Regulated Heterocyst Differentiation Genes hetC and devB from Anabaena sp. Strain PCC 7120 Exhibit a Similar Tandem Promoter Arrangement{triangledown}

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

Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, E-41092 Seville, Spain

Received 12 May 2009/ Accepted 2 July 2009

Transcription of the hetC gene, whose product is required for heterocyst differentiation, takes place from a long promoter region that includes the previously described HetR-independent, NtcA-activated promoter producing transcripts with a 5' end corresponding to position –571 with respect to the translational start site of hetC. Northern blot analysis indicated that the accumulation of hetC transcripts depends on HetR, and a second transcriptional start site located at position –293 that leads to NtcA-dependent, HetR-dependent inducible transcription of hetC was identified. Upon nitrogen stepdown, expression of a PhetC::gfp fusion was transiently induced in specific cells that were differentiating into heterocysts, both when the whole promoter region (containing transcription start points –571 and –293) or a short version (containing only the transcription start point –293) was used. Expression of hetC from the –293 position was delayed in a strain bearing a deleted promoter region lacking sequences upstream from position –570. Such a strain was still able to differentiate functional heterocysts and to grow diazotrophically, although diazotrophic growth was impaired under certain conditions. Similarly, a second, NtcA-dependent, HetR-dependent transcriptional start site was identified at position –454 in the promoter region upstream from the devBCA operon encoding an ABC transport system involved in heterocyst maturation, in which an NtcA-dependent promoter producing transcripts starting at position –704 had been previously noted. Thus, the hetC and devBCA promoter regions exhibit similar tandem promoter arrangements.

* Corresponding author. Mailing address: Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la Cartuja, Avda. Américo Vespucio 49, E-41092 Seville, Spain. Phone: 34 95 448 9521. Fax: 34 95 446 0065. E-mail: alicia{at}ibvf.csic.es

{triangledown} Published ahead of print on 10 July 2009.

Journal of Bacteriology, September 2009, p. 5765-5774, Vol. 191, No. 18
0021-9193/09/$08.00+0     doi:10.1128/JB.00616-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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