title: Hfq is required for optimal nitrate assimilation in the Cyanobacterium Anabaena sp. strain PCC 7120.
abstract: Hfq is an RNA binding protein involved in posttranscriptional regulation of gene expression in bacteria. It acts by binding to regulatory small RNAs (sRNAs), which confer specificity for the regulation. Recently, orthologues of the Hfq protein were annotated in cyanobacterial genomes, although its capacity to regulate gene expression by interacting with sRNAs has not been yet demonstrated. Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that, in the absence of combined nitrogen, is able to fix atmospheric nitrogen by differentiating specialized cells called heterocysts. We have generated an hfq knockout mutant of Anabaena sp. PCC 7120. Deletion of this gene results in differentiation of heterocysts in the presence of nitrate, suggesting a defect in nitrate assimilation. We show that hfq mutant cells are affected in transport and use of nitrate and nitrite. An analysis of the expression of several genes in the nir operon, encoding different elements of the nitrate assimilation pathway, demonstrates a downregulation of their transcription in mutant cells. We also observed that genes ntcB and cnaT, involved in the regulation of the nir operon, show a lower expression in cells lacking Hfq. Finally, when hfq was reintroduced in the mutant, heterocyst differentiation was no longer observed in the presence of nitrate. Therefore, our results indicate that the RNA chaperone Hfq is involved in the regulation of the nir operon, although the mechanism for this regulation is still unknown.
authors: Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Avda Reina Mercedes 6, 41012 Seville, Spain. epuerta@us.es
authors: Elena
authors: E
authors: Puerta-Fernández
authors: Agustín
authors: A
authors: Vioque
references: J Bacteriol. 1997 Jan;179(2):477-86
references: 8990301
references: J Bacteriol. 2003 Sep;185(17):5037-44
references: 12923076
references: Mol Microbiol. 2006 Aug;61(4):1013-22
references: 16859494
references: Curr Opin Microbiol. 2000 Apr;3(2):154-8
references: 10744991
references: RNA. 2007 Dec;13(12):2053-60
references: 17901153
references: J Bacteriol. 2010 Jun;192(11):2769-78
references: 20348260
references: Genes Dev. 1996 May 1;10(9):1143-51
references: 8654929
references: J Bacteriol. 1997 Mar;179(6):1998-2005
references: 9068647
references: Nat Rev Microbiol. 2010 Jan;8(1):39-50
references: 19966815
references: J Bacteriol. 1997 Jan;179(1):258-66
references: 8982006
references: Nucleic Acids Res. 2007;35(3):999-1006
references: 17259214
references: Nature. 1968 Aug 10;219(5154):588-90
references: 4874917
references: J Bacteriol. 1990 Jun;172(6):3138-45
references: 2160938
references: Anal Biochem. 1978 Jun 15;87(1):206-10
references: 98070
references: BMC Microbiol. 2007 Feb 09;7:10
references: 17291347
references: Nucleic Acids Res. 1997 Sep 1;25(17):3471-7
references: 9254706
references: Mol Microbiol. 2000 Nov;38(3):613-25
references: 11069684
references: Photosynth Res. 2002;72(1):13-26
references: 16228531
references: J Bacteriol. 2007 Jun;189(12):4425-30
references: 17416650
references: Annu Rev Microbiol. 2004;58:303-28
references: 15487940
references: Curr Opin Microbiol. 2010 Feb;13(1):24-33
references: 20080057
references: J Bacteriol. 1995 Jun;177(11):3150-7
references: 7768813
references: BMC Mol Biol. 2010 Feb 18;11:17
references: 20167073
references: J Exp Bot. 2002 Aug;53(375):1689-98
references: 12147719
references: Mol Microbiol. 2004 Mar;51(6):1525-33
references: 15009882
references: Methods Enzymol. 1988;167:747-54
references: 3148842
references: Mol Microbiol. 1992 Nov;6(22):3452-4
references: 1484496
references: Mol Microbiol. 1993 Jul;9(1):77-84
references: 8412673
references: FEBS J. 2009 Jul;276(14):3904-15
references: 19777643
references: Nucleic Acids Res. 2002 Sep 1;30(17):3662-71
references: 12202750
references: J Biol Chem. 2004 Jul 30;279(31):32212-8
references: 15166246
references: Photosynth Res. 2005;83(2):117-33
references: 16143847
references: Mol Microbiol. 1994 Jul;13(1):35-49
references: 7984093
references: Gene. 1988 Aug 15;68(1):119-38
references: 2851487
references: J Bacteriol. 1997 Jan;179(1):297-300
references: 8982015
references: J Bacteriol. 1995 Jan;177(2):290-6
references: 7814317
references: Microbiology (Reading). 2008 Oct;154(Pt 10):3134-3143
references: 18832319
references: Mol Cell. 2002 Jan;9(1):23-30
references: 11804583
references: J Bacteriol. 1996 Jul;178(13):3893-8
references: 8682795
references: Mol Microbiol. 2005 Dec;58(5):1421-9
references: 16313626
references: RNA. 2008 Sep;14(9):1907-17
references: 18658123
references: Appl Environ Microbiol. 2003 Dec;69(12):7009-18
references: 14660343
references: J Bacteriol. 2005 Mar;187(6):1985-91
references: 15743946
references: Mol Cell. 2002 Jan;9(1):11-22
references: 11804582