Tic32, an essential component in chloroplast biogenesis.
Chloroplast protein import across the inner envelope is facilitated by the translocon of the inner envelope of chloroplasts (Tic). Here we have identified Tic32 as a novel subunit of the Tic complex. Tic32 can be purified from solubilized inner envelope membranes by chromatography on Tic110 containing affinity matrix. Co-immunoprecipitation experiments using either Tic32 or Tic110 antisera indicated a tight association between these polypeptides as well as with other Tic subunits, e.g. Tic40, Tic22, or Tic62, whereas the outer envelope protein Toc75 was not found in this complex. Chemical cross-linking suggests that Tic32 is involved late in the overall translocation process, because both the precursor form as well as the mature form of Rubisco small subunit can be detected. We were unable to isolate Arabidopsis null mutants of the attic32 gene, indicating that Tic32 is essential for viability. Deletion of the attic32 gene resulted in early seed abortion because the embryo was unable to differentiate from the heart stage to the torpedo stage. The homology of Tic32 to short-chain dehydrogenases suggests a dual role of Tic32 in import, one as a regulatory component and one as an important subunit in the assembly of the entire complex.
Hörmann
Friederike
F
Department of Biology and Plant Biochemistry, University of Munich, Menzinger Strasse 67, 80638 Munich, Germany.
Küchler
Michael
M
Sveshnikov
Dmitry
D
Oppermann
Udo
U
Li
Yong
Y
Soll
Jürgen
J
D000595:Amino Acid Sequence; D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division; D002736:Chloroplasts / Q000378:metabolism / Q000502:physiology*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D015723:Gene Library; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D026901:Membrane Transport Proteins; D008957:Models, Genetic; D018832:Molecular Chaperones / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D018532:Pisum sativum; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D018076:DNA, Complementary; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D018832:Molecular Chaperones; D010940:Plant Proteins; C116001:Tic22 protein, Pisum sativum; C490375:Tic32 protein, Arabidopsis; C476397:Tic40 protein, Arabidopsis