title: The heterocyst differentiation transcriptional regulator HetR of the filamentous cyanobacterium Anabaena forms tetramers and can be regulated by phosphorylation.
abstract: Many filamentous cyanobacteria respond to the external cue of nitrogen scarcity by the differentiation of heterocysts, cells specialized in the fixation of atmospheric nitrogen in oxic environments. Heterocysts follow a spatial pattern along the filament of two heterocysts separated by ca. 10-15 vegetative cells performing oxygenic photosynthesis. HetR is a transcriptional regulator that directs heterocyst differentiation. In the model strain Anabaena sp. PCC 7120, the HetR protein was observed in various oligomeric forms in vivo, including a tetramer that peaked with maximal hetR expression during differentiation. Tetramers were not detected in a hetR point mutant incapable of differentiation, but were conspicuous in an over-differentiating strain lacking the PatS inhibitor. In differentiated filaments the HetR tetramer was restricted to heterocysts, being undetectable in vegetative cells. HetR co-purified with RNA polymerase from Anabaena mainly as a tetramer. In vitro, purified recombinant HetR was distributed between monomers, dimers, trimers and tetramers, and it was phosphorylated when incubated with (γ-(32)P)ATP. Phosphorylation and PatS hampered the accumulation of HetR tetramers and impaired HetR binding to DNA. In summary, tetrameric HetR appears to represent a functionally relevant form of HetR, whose abundance in the Anabaena filament could be negatively regulated by phosphorylation and by PatS.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, Universidad de Sevilla, Américo Vespucio 49, E-41092, Seville, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Valladares
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, Universidad de Sevilla, Américo Vespucio 49, E-41092, Seville, Spain.
authors.forename: Enrique
authors.initials: E
authors.lastname: Flores
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, Universidad de Sevilla, Américo Vespucio 49, E-41092, Seville, Spain.
authors.forename: Antonia
authors.initials: A
authors.lastname: Herrero
mesh_terms: D017033:Anabaena / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D009584:Nitrogen / Q000378:metabolism; D010766:Phosphorylation; D017354:Point Mutation; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; C067403:HetR protein, Bacteria; D009584:Nitrogen