title: Identification of the chloroplast adenosine-to-inosine tRNA editing enzyme.
abstract: Plastids (chloroplasts) of higher plants exhibit two types of conversional RNA editing: cytidine-to-uridine editing in mRNAs and adenosine-to-inosine editing in at least one plastid genome-encoded tRNA, the tRNA-Arg(ACG). The enzymes catalyzing RNA editing reactions in plastids are unknown. Here we report the identification of the A-to-I tRNA editing enzyme from chloroplasts of the model plant Arabidopsis thaliana. The protein (AtTadA) has an unusual structure in that it harbors a large N-terminal domain of >1000 amino acids, which is not required for catalytic activity. The C-terminal region of the protein displays sequence similarity to tadA, the tRNA adenosine deaminase from Escherichia coli. We show that AtTadA is imported into chloroplasts in vivo and demonstrate that the in vitro translated protein triggers A-to-I editing in the anticodon of the plastid tRNA-Arg(ACG). Suppression of AtTadA gene expression in transgenic Arabidopsis plants by RNAi results in reduced A-to-I editing in the chloroplast tRNA-Arg(ACG). The RNAi lines display a mild growth phenotype, presumably due to reduced chloroplast translational efficiency upon limited availability of edited tRNA-Arg(ACG).
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, D-14476 Potsdam-Golm, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Karcher
authors.forename: Ralph
authors.initials: R
authors.lastname: Bock
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000235:genetics / Q000378:metabolism*; D058892:Adenosine Deaminase Inhibitors; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D007288:Inosine / Q000378:metabolism*; D008969:Molecular Sequence Data; D017393:RNA Editing; D018749:RNA, Plant / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions
chemical_list: D058892:Adenosine Deaminase Inhibitors; D029681:Arabidopsis Proteins; D018744:DNA, Plant; D018749:RNA, Plant; D034741:RNA, Small Interfering; D012346:RNA, Transfer, Amino Acyl; D007288:Inosine; D000243:Adenosine Deaminase; D000241:Adenosine