title: Alkane Biosynthesis Genes in Cyanobacteria and Their Transcriptional Organization.
abstract: In cyanobacteria, alkanes are synthesized from a fatty acyl-ACP by two enzymes, acyl-acyl carrier protein reductase and aldehyde deformylating oxygenase. Despite the great interest in the exploitation for biofuel production, nothing is known about the transcriptional organization of their genes or the physiological function of alkane synthesis. The comparison of 115 microarray datasets indicates the relatively constitutive expression ofaarandadogenes. The analysis of 181 available genomes showed that in 90% of the genomes both genes are present, likely indicating their physiological relevance. In 61% of them they cluster together with genes encoding acetyl-CoA carboxyl transferase and a short-chain dehydrogenase, strengthening the link to fatty acid metabolism and in 76% of the genomes they are located in tandem, suggesting constraints on the gene arrangement. However, contrary to the expectations for an operon, we found inSynechocystissp. PCC 6803 specific promoters for the two genes,sll0208(ado) andsll0209(aar), which give rise to monocistronic transcripts. Moreover, the upstream locatedadogene is driven by a proximal as well as a second, distal, promoter, from which a third transcript, the ~160 nt sRNA SyR9 is transcribed. Thus, the transcriptional organization of the alkane biosynthesis genes inSynechocystissp. PCC 6803 is of substantial complexity. We verified all three promoters to function independently from each other and show a similar promoter arrangement also in the more distantNodularia spumigena,Trichodesmium erythraeum,Anabaenasp. PCC 7120,ProchlorococcusMIT9313, and MED4. The presence of separate regulatory elements and the dominance of monocistronic mRNAs suggest the possible autonomous regulation ofadoandaar. The complex transcriptional organization of the alkane synthesis gene cluster has possible metabolic implications and should be considered when manipulating the expression of these genes in cyanobacteria.
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Klähn
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Desirée
authors.initials: D
authors.lastname: Baumgartner
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Pfreundt
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Voigt
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Schön
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Steglich
authors.affiliation: Genetics and Experimental Bioinformatics, Institute of Biology 3, Faculty of Biology, University of Freiburg , Freiburg , Germany.
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Hess
keywords: alkane biosynthesis; cyanobacteria; operon; promoter; sRNA; start sites of transcription