Arabidopsis inositol polyphosphate 6-/3-kinase is a nuclear protein that complements a yeast mutant lacking a functional ArgR-Mcm1 transcription complex.
Inositol 1,4,5-trisphosphate 3-kinase, and more generally inositol polyphosphate kinases (Ipk), play important roles in signal transduction in animal cells; however, their functions in plant cells remain to be elucidated. Here, we report the molecular cloning of a cDNA (AtIpk2beta) from a higher plant, Arabidopsis. Arabidopsis AtIpk2beta is a 33-kD protein that exhibits weak homology ( approximately 25% identical amino acids) with Ipk proteins from animals and yeast and lacks a calmodulin binding site, as revealed by sequence analysis and calmodulin binding assays. However, recombinant AtIpk2beta phosphorylates inositol 1,4,5-trisphosphate to inositol 1,4,5,6-tetrakisphosphate and also converts it to inositol 1,3,4,5,6-pentakisphosphate [Ins(1,3,4,5,6)P(5)]. AtIpk2beta also phosphorylates inositol 1,3,4,5-tetrakisphosphate to Ins(1,3,4,5,6)P(5). Thus, the enzyme is a D3/D6 dual-specificity inositol phosphate kinase. AtIpk2beta complements a yeast ARG82/IPK2 mutant lacking a functional ArgR-Mcm1 transcription complex. This complex is involved in regulating Arg metabolism-related gene expression and requires inositol polyphosphate kinase activity to function. AtIpk2beta was found to be located predominantly in the nucleus of plant cells, as demonstrated by immunolocalization and fusion to green fluorescent protein. RNA gel blot analysis and promoter-beta-glucuronidase reporter gene studies demonstrated AtIpk2beta gene expression in various organs tested. These data suggest a role for AtIpk2beta as a transcriptional control mediator in plants.
Xia
Hui-Jun
HJ
Max-Planck-Institute of Molecular Plant Physiology, D-14424 Potsdam, Germany.
Brearley
Charles
C
Elge
Stephan
S
Kaplan
Boaz
B
Fromm
Hillel
H
Mueller-Roeber
Bernd
B
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D001120:Arginine / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins; D007295:Inositol Phosphates / Q000096:biosynthesis; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D026341:Minichromosome Maintenance 1 Protein / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
C067875:ARG81 protein, S cerevisiae; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D007295:Inositol Phosphates; D008164:Luminescent Proteins; D026341:Minichromosome Maintenance 1 Protein; D009687:Nuclear Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C451920:inositol-1,3,4,5,6-pentakisphosphate; C081655:inositol-1,3,4,5-tetrakisphosphate; D049452:Green Fluorescent Proteins; D001120:Arginine; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; C056875:myo-inositol-trisphosphate 6-kinase