Tic40, a new "old" subunit of the chloroplast protein import translocon.
The protein import translocon at the inner envelope of chloroplasts (Tic complex) is a heteroligomeric multisubunit complex. Here, we describe Tic40 from pea as a new component of this complex. Tic40 from pea is a homologue of a protein described earlier from Brassica napus as Cim/Com44 or the Toc36 subunit of the translocon at the outer envelope of chloroplasts, respectively (Wu, C., Seibert, F. S., and Ko, K. (1994) J. Biol. Chem. 269, 32264-32271; Ko, K., Budd, D., Wu, C., Seibert, F., Kourtz, L., and Ko, Z. W. (1995) J. Biol. Chem. 270, 28601-28608; Pang, P., Meathrel, K., and Ko, K. (1997) J. Biol. Chem. 272, 25623-25627). Tic40 can be covalently connected to Tic110 by the formation of a disulfide bridge under oxidizing conditions, indicating its close physical proximity to an established translocon component. The Tic40 protein is synthesized in the cytosol as a precursor with an N-terminal cleavable chloroplast targeting signal and imported into the organelle via the general import pathway. Immunoblotting and immunogold-labeling studies exclusively confine Tic40 to the chloroplastic inner envelope, in which it is anchored by a single putative transmembrane span.
Stahl
T
T
Botanisches Institut, Universität Kiel, 24118 Kiel, Germany.
Glockmann
C
C
Soll
J
J
Heins
L
L
D000595:Amino Acid Sequence; D001692:Biological Transport; D002736:Chloroplasts / Q000737:chemistry* / Q000378:metabolism; D018076:DNA, Complementary / Q000302:isolation & purification; D008565:Membrane Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000737:chemistry*; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
D018076:DNA, Complementary; D008565:Membrane Proteins; D010940:Plant Proteins