Abstract:
The 32 kDa chloroplast inner envelope protein (IEP32) is
imported into the organelle in the absence of a cleavable Nterminal pre-sequence. The ten N-terminal amino acids
form an essential portion of this targeting information
as deduced from deletion mutants. Recognition and
translocation of IEP32 is not catalysed by the general
chloroplast outer envelope translocon subunits Toc159,
Toc75III and Toc34, because IEP32 import is neither
inhibited by proteolytic removal of Toc34 and Toc159 nor
by inhibition of the Toc75 import channel by CuCl2
or spermine. Import of IEP32 only requires ATP
concentrations of below 20 µM indicating that stromal
chaperones are not involved in the process, but that IEP32
might be directly inserted from the intermembrane space
into the inner envelope by a so far unidentified pathway.
IEP32 may require the assistance of Tic22, an
intermembrane space translocon subunit for import as
indicated by the presence of a chemical crosslinked product
between both polypeptides.