Still, in some experiments the promoter activity was abolished wh

Still, in some experiments the promoter activity was abolished while others showed only a low activity – a finding that deserves further attention. In this paper we have shown that the part of the hupSL promoter region that gave the highest expression level is limited to a 316 bp DNA fragment stretching from -57 (in relation to tsp) to the translation start site (Fig. 4). Not only does this short promoter confer a high MK-0457 manufacturer transcription level, it also retains

heterocyst specificity. A loss of heterocyst specificity could have lead to a misleading conclusion of high promoter activity: the promoter would have shown high total expression, due to expression in all cells, even if the promoter activity was still low. However the fact that this promoter fragment kept heterocyst specificity (Fig. 5) enables us to draw the conclusion that the activity of the shortest promoter is truly higher than for the other promoter fragments. One assumption could be that heterocyst specificity of expression is due to a transcription factor binding to the hupSL promoter

and stimulating transcription in heterocysts. However, another possibility could be that hupSL is constitutively LCL161 transcribed and that vegetative cells contain a repressor lacking in heterocysts which restrain transcription in that cell type. If the heterocyst specificity is mediated by an activator binding the short promoter sequence upstream the tsp (or perhaps the untranslated leader region downstream the tsp) or by a repressor only present in vegetative cells needs to be subjected to further investigations. Further characterization of

this short promoter region will not only give information about what promotes hupSL transcription but can also help answering the question what directs heterocyst specific expression of genes and pattern formation in N. punctiforme, and perhaps other heterocystous, filamentous cyanobacteria. Conclusion The result that the 57 bp promoter is a highly active promoter is most interesting and will be investigated further. This short DNA sequence, and its 258 bp untranslated leader region Dipeptidyl peptidase downstream the tsp, appears to harbour enough information to make the transcription to occur in heterocysts only. Taken one step further, if this information conferring heterocyst specific transcription can be elucidated it will give clues to what signals are involved in heterocyst specific gene expression and pattern formation in filamentous cyanobacteria. Acknowledgements This work was supported by the Swedish Energy Agency, the Knut and Alice Wallenberg Foundation, the Nordic Energy Research Program (project BioH2), EU/NEST FP6 project BioModularH2 (contract # 043340) and the EU/Energy FP7 project SOLAR-H2 (contract # 212508). References 1. Tamagnini P, Axelsson R, Lindberg P, Oxelfelt F, Wunschiers R, Lindblad P: Hydrogenases and hydrogen metabolism of cyanobacteria. Microbiol Mol Biol Rev 2002,66(1):1–20.PubMedCrossRef 2.

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