title: Requirement of Fra proteins for communication channels between cells in the filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120.
abstract: The filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120 differentiates specialized cells, heterocysts, that fix atmospheric nitrogen and transfer the fixed nitrogen to adjacent vegetative cells. Reciprocally, vegetative cells transfer fixed carbon to heterocysts. Several routes have been described for metabolite exchange within the filament, one of which involves communicating channels that penetrate the septum between adjacent cells. Several fra gene mutants were isolated 25 y ago on the basis of their phenotypes: inability to fix nitrogen and fragmentation of filaments upon transfer from N+ to N- media. Cryopreservation combined with electron tomography were used to investigate the role of three fra gene products in channel formation. FraC and FraG are clearly involved in channel formation, whereas FraD has a minor part. Additionally, FraG was located close to the cytoplasmic membrane and in the heterocyst neck, using immunogold labeling with antibody raised to the N-terminal domain of the FraG protein.
authors.affiliation: Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637;
authors.forename: Amin
authors.initials: A
authors.lastname: Omairi-Nasser
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, E-41092 Seville, Spain;
authors.forename: Vicente
authors.initials: V
authors.lastname: Mariscal
authors.affiliation: Advanced Electron Microscopy Facility, The University of Chicago, Chicago, IL 60637.
authors.forename: Jotham R
authors.initials: JR
authors.lastname: Austin
authors.affiliation: Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637; rh01@uchicago.edu.
authors.forename: Robert
authors.initials: R
authors.lastname: Haselkorn
mesh_terms: D017033:Anabaena / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009586:Nitrogen Fixation; D013347:Subcellular Fractions / Q000378:metabolism; D014054:Tomography
chemical_list: D001426:Bacterial Proteins; C092495:FraC protein, Anabaena; C024250:cyanophycin
keywords: Fra proteins; cell communication; channels; cyanobacteria