AtToc90, a new GTP-binding component of the Arabidopsis chloroplast protein import machinery.
AtToc159 is a GTP-binding chloroplast protein import receptor. In vivo, atToc159 is required for massive accumulation of photosynthetic proteins during chloroplast biogenesis. Yet, in mutants lacking atToc159 photosynthetic proteins still accumulate, but at strongly reduced levels whereas non-photosynthetic proteins are imported normally: This suggests a role for the homologues of atToc159 (atToc132, -120 and -90). Here, we show that atToc90 supports accumulation of photosynthetic proteins in plastids, but is not required for import of several constitutive proteins. Part of atToc90 associates with the chloroplast surface in vivo and with the Toc-complex core components (atToc75 and atToc33) in vitro suggesting a function in chloroplast protein import similar to that of atToc159. As both proteins specifically contribute to the accumulation of photosynthetic proteins in chloroplasts they may be components of the same import pathway.
Albert-Ludwigs-Universität Freiburg, Institut für Biologie II/Botanik, Schänzlestrasse 1, D-79104 Freiburg, Germany.
Andreas
A
Hiltbrunner
Kathrin
K
Grünig
Mayte
M
Alvarez-Huerta
Sibylle
S
Infanger
Jörg
J
Bauer
Felix
F
Kessler
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002736:Chloroplasts / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D049452:Green Fluorescent Proteins; D008027:Light; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D011485:Protein Binding; D021381:Protein Transport; D011523:Protoplasts / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015854:Up-Regulation / Q000528:radiation effects
D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D008164:Luminescent Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C036483:T-DNA; C114786:Toc33 protein, Arabidopsis; C491156:Toc90 protein, Arabidopsis; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins