title: The NtcA-regulated amtB gene is necessary for full methylammonium uptake activity in the cyanobacterium Synechococcus elongatus.
abstract: The Amt proteins constitute a ubiquitous family of transmembrane ammonia channels that permit the net uptake of ammonium by cells. In many organisms, there is more than one amt gene, and these genes are subjected to nitrogen control. The mature Amt protein is a homo- or heterooligomer of three Amt subunits. We previously characterized an amt1 gene in the unicellular cyanobacterium Synechococcus elongatus strain PCC 7942. In this work, we describe the presence in this organism of a second amt gene, amtB, which encodes a protein more similar to the bacterial AmtB proteins than to any other characterized cyanobacterial Amt protein. The expression of amtB took place in response to nitrogen step-down, required the NtcA transcription factor, and occurred parallel to the expression of amt1. However, the transcript levels of amtB measured after 2 h of nitrogen deprivation were about 100-fold lower than those of amt1. An S. elongatus amtB insertional mutant exhibited an activity for uptake of [14C]methylammonium that was about 55% of that observed in the wild type, but inactivation of amtB had no noticeable effect on the uptake of ammonium when it was supplied at a concentration of 100 microM or more. Because an S. elongatus amt1 mutant is essentially devoid of [14C]methylammonium uptake activity, the mature Amt transporter is functional in the absence of AmtB subunits but not in the absence of Amt1 subunits. However, the S. elongatus amtB mutant could not concentrate [14C]methylammonium within the cells to the same extent as the wild type. Therefore, AmtB is necessary for full methylammonium uptake activity in S. elongatus.
authors: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla, Spain.
authors: Javier
authors: J
authors: Paz-Yepes
authors: Antonia
authors: A
authors: Herrero
authors: Enrique
authors: E
authors: Flores
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007700:Kinetics; D008744:Methylamines / Q000378:metabolism*; D010802:Phylogeny; D012334:RNA, Neoplasm / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics; D046940:Synechococcus / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D017931:DNA Primers; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D008744:Methylamines; D012334:RNA, Neoplasm; D012097:Repressor Proteins; D014157:Transcription Factors; C075617:ntcA protein, Synechococcus; C027451:methylamine
references: Mol Microbiol. 2000 Jan;35(2):378-85
references: 10652098
references: Anal Biochem. 1978 Jun 15;87(1):206-10
references: 98070
references: J Bacteriol. 2001 Jan;183(2):411-25
references: 11133933
references: Microbiology. 2001 Jan;147(Pt 1):135-43
references: 11160807
references: FEBS Lett. 2002 Feb 13;512(1-3):71-4
references: 11852054
references: Microbiology. 2002 Mar;148(Pt 3):861-9
references: 11882722
references: FEBS Lett. 2003 May 22;543(1-3):42-6
references: 12753902
references: J Biol Chem. 2003 Nov 14;278(46):45603-10
references: 12952951
references: Science. 2004 Sep 10;305(5690):1587-94
references: 15361618
references: J Biol Chem. 1970 Sep 10;245(17):4241-50
references: 5498410
references: Arch Microbiol. 1975;102(1):13-21
references: 235244
references: J Bacteriol. 1983 Nov;156(2):752-7
references: 6138344
references: J Bacteriol. 1984 Apr;158(1):36-42
references: 6425267
references: J Bacteriol. 1984 Oct;160(1):204-10
references: 6434519
references: Gene. 1988 Aug 15;68(1):119-38
references: 2851487
references: J Bacteriol. 1990 Jun;172(6):3138-45
references: 2160938
references: Plant Mol Biol. 1990 Nov;15(5):723-33
references: 2129399
references: Nucleic Acids Res. 1992 Feb 25;20(4):911
references: 1371871
references: EMBO J. 1994 Jun 15;13(12):2862-9
references: 8026471
references: EMBO J. 1994 Aug 1;13(15):3464-71
references: 8062823
references: Nucleic Acids Res. 1994 Nov 11;22(22):4673-80
references: 7984417
references: Mol Microbiol. 1995 May;16(4):657-67
references: 7476161
references: Biochimie. 1996;78(5):364-9
references: 8905155
references: J Bacteriol. 1997 Jan;179(2):477-86
references: 8990301
references: Biophys J. 1997 May;72(5):2187-95
references: 9129821
references: Mol Cell Biol. 1997 Aug;17(8):4282-93
references: 9234685
references: Plant Mol Biol. 1997 Dec;35(6):723-34
references: 9426594
references: Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):7030-4
references: 9618533
references: J Biol Chem. 1998 Nov 20;273(47):31463-70
references: 9813059
references: Proc Natl Acad Sci U S A. 2004 Dec 7;101(49):17090-5
references: 15563598
references: Biochem Soc Trans. 2005 Feb;33(Pt 1):164-7
references: 15667295
references: Biochem J. 2005 Aug 15;390(Pt 1):215-22
references: 15876187
references: Proc Natl Acad Sci U S A. 2005 Oct 18;102(42):14994-9
references: 16214888
references: J Gen Physiol. 2006 Feb;127(2):133-44
references: 16446503
references: Transfus Clin Biol. 2006 Mar-Apr;13(1-2):111-6
references: 16563830
references: J Biol Chem. 1978 May 10;253(9):3287-91
references: 417083
references: FEBS Lett. 2000 Feb 11;467(2-3):273-8
references: 10675553