Thu, 24 Jul 2008 21:56:16 BST CiteULike: di cbg Valladares http://www.citeulike.org/user/cbg/author/Valladares CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/cbg/article/2776005 <i>Molecular Microbiology, Vol. 44, No. 5. (2002), pp. 1377-1385.</i><br /><br />Summary Heterocyst differentiation in the cyanobacterium Anabaena sp. strain PCC 7120 depends on both the global nitrogen regulator NtcA and the cell differentiation regulatory protein HetR, and induction of hetR upon nitrogen step-down depends on NtcA. The use of two out of the four transcription start points (tsps) described for the hetR gene (those located at positions -728 and -271) was found to be dependent on NtcA, and the use of the tsp located at position -271 was also dependent on HetR. Thus, autoregulation of hetR could take place via the activation of transcription from this tsp. Expression of ntcA in nitrogen-fixing cultures was higher than in cells growing in the presence of ammonium or nitrate, and high expression of ntcA under nitrogen deficiency resulted from an increased use of tsps located at positions -180 and -49. The induction of the use of these tsps did not take place in ntcA or hetR mutant strains. These results indicate a mutual dependency in the induction of the regulatory genes hetR and ntcA that takes place in response to nitrogen step-down in Anabaena cells. Expression of the hetC gene, which is also involved in the early steps of heterocyst differentiation, from its NtcA-dependent tsp was, however, not dependent on HetR. Mutual dependence of the expression of the cell differentiation regulatory protein HetR and the global nitrogen regulator NtcA during heterocyst development Alicia Ana Valladares Enrique Flores Antonia Herrero doi:10.1046/j.1365-2958.2002.02970.x Molecular Microbiology, Vol. 44, No. 5. (2002), pp. 1377-1385. 2008-05-09T14:33:23-00:00 2002 Molecular Microbiology 44 5 1377 1385 biochempaper cyanobacteria hetr ntca http://www.citeulike.org/user/cbg/article/2679233 <i>J. Bacteriol., Vol. 181, No. 21. (1 November 1999), pp. 6664-6669.</i><br /><br />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. The hetC Gene Is a Direct Target of the NtcA Transcriptional Regulator in Cyanobacterial Heterocyst Development Alicia Muro-Pastor Ana Valladares Enrique Flores Antonia Herrero J. Bacteriol., Vol. 181, No. 21. (1 November 1999), pp. 6664-6669. 2008-04-17T00:24:44-00:00 1999 J. Bacteriol. 181 21 6664 6669 biochempaper heterocyst