title: Subcellular localization and clues for the function of the HetN factor influencing heterocyst distribution in Anabaena sp. strain PCC 7120.
abstract: In the filamentous cyanobacterium Anabaena sp. strain PCC 7120, heterocysts are formed in the absence of combined nitrogen, following a specific distribution pattern along the filament. The PatS and HetN factors contribute to the heterocyst pattern by inhibiting the formation of consecutive heterocysts. Thus, inactivation of any of these factors produces the multiple contiguous heterocyst (Mch) phenotype. Upon N stepdown, a HetN protein with its C terminus fused to a superfolder version of green fluorescent protein (sf-GFP) or to GFP-mut2 was observed, localized first throughout the whole area of differentiating cells and later specifically on the peripheries and in the polar regions of mature heterocysts, coinciding with the location of the thylakoids. Polar localization required an N-terminal stretch comprising residues 2 to 27 that may represent an unconventional signal peptide. Anabaena strains expressing a version of HetN lacking this fragment from a mutant gene placed at the native hetN locus exhibited a mild Mch phenotype. In agreement with previous results, deletion of an internal ERGSGR sequence, which is identical to the C-terminal sequence of PatS, also led to the Mch phenotype. The subcellular localization in heterocysts of fluorescence resulting from the fusion of GFP to the C terminus of HetN suggests that a full HetN protein is present in these cells. Furthermore, the full HetN protein is more conserved among cyanobacteria than the internal ERGSGR sequence. These observations suggest that HetN anchored to thylakoid membranes in heterocysts may serve a function besides that of generating a regulatory (ERGSGR) peptide.
authors: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Seville, Spain.
authors: Laura
authors: L
authors: Corrales-Guerrero
authors: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Seville, Spain.
authors: Vicente
authors: V
authors: Mariscal
authors: School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
authors: Dennis J
authors: DJ
authors: Nürnberg
authors: Center for the Study of Biological Complexity, Virginia Commonwealth University, Richmond, Virginia, USA.
authors: Jeff
authors: J
authors: Elhai
authors: School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
authors: Conrad W
authors: CW
authors: Mullineaux
authors: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Seville, Spain.
authors: Enrique
authors: E
authors: Flores
authors: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Seville, Spain herrero@ibvf.csic.es.
authors: Antonia
authors: A
authors: Herrero
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D042541:Intracellular Space / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D010088:Oxidoreductases; C107239:HetN protein, Anabaena