320:	Analysis of the genes encoding selected components of the Arabidopsis chloroplast protein import apparatus.

Authors:	Jackson, Diane, T.(A)Keegstra, Kenneth(A)
Affiliations:	(A): Michigan State University-DOE Plant Research Laboratory, Michigan State University
Presenter:	Jackson, Diane T., jacks282@pilot.msu.edu

Current models concerning the protein import apparatus of the chloroplast envelope implicate at least seven, and possibly eight, polypeptides as being components of the import machinery. These include three outer membrane proteins (Toc159, Toc75, Toc34), three or four inner membrane proteins (Tic110, Tic22, Tic20, Tic55), and one stromal molecular chaperone (ClpC). Unfortunately, identification of these components has not, in most cases, been accompanied by an experimental determination of their molecular function. In order to address this question, we plan to analyze Arabidopsis mutants that have had the genes for one or more of these components disrupted. Since most of the in vitro work on chloroplast protein import has been performed using isolated pea chloroplasts, virtually all of the known constituents of the translocation machinery were originally cloned from pea. In order to genetically manipulate the genes for the import components in Arabidopsis, it first needs to be established whether homologous genes can be identified in this system, and if so, how their sequences compare to those derived from pea. Genomic sequences for Toc159, Toc34, Tic20, and ClpC are currently available; sequence information, in the form of genomic and/or EST clones, may possibly exist for two other components (Toc75 and Tic110). In addition to an analysis of these available sequences, this report will also present experimental results concerning the copy number of genes encoding known components of the translocation machinery in Arabidopsis and our preliminary work in the identification of disruptions in genes encoding selected components. This research has been funded by the National Science Foundation and the U.S. Department of Energy.