Poster: Organelle biogenesis

Abs # 628: Functional analysis of Tic40, an inner envelope membrane component of the chloroplast protein import apparatus

Presenter:	Chou, Ming-Lun , mlchou@gate.sinica.edu.tw
Authors	Chou, Ming-Lun  (A)   Li, Hsou-min  (A)
Affiliations:	(A): Institute of Molecular Biology, Academia Sinica,

Most chloroplast proteins are post-translationally imported from the cytosol through a translocon complex located in the chloroplast envelope. Translocon components in the outer membrane are named as Toc (translocon at the outer-envelope-membrane of chloroplasts) proteins and those in the inner membrane are named as Tic (translocon at the inner-envelope-membrane of chloroplasts) proteins. We have analysed an Arabidopsis T-DNA-tagged tic40 mutant. Protein import and cross-linking experiments demonstrated that Tic40 was part of the Tic/Toc translocon complex. The C-terminal half of Tic40's hydrophilic domain is composed of a TPR domain followed by domain shared by co-chaperones Sti1p/Hop and Hip. From these data, we propose that Tic40 functions as a co-chaperone in the stromal chaperone complex that facilitates protein translocation across the inner membrane. Interacting domains among Tic40 and proteins that are known to associate with Tic40 are being mapped by yeast two-hybrid and in vitro pull-down assays. Functional significance of these interactions will also be analyzed. This research is supported by grants to H-m Li from the Academia Sinica and National Science Council of Taiwan.