Chloroplast TatC plays a direct role in thylakoid ΔpH-dependent protein transport

The thylakoid Delta pH-dependent pathway transports folded proteins. Identified components include Hcf106 and Tha4. Orthologs of these proteins plus a membrane protein called TatC are essential for the homologous bacterial Tat system, Here we report identification of a chloroplast TatC (cpTatC). cpTatC is an integral thylakoid membrane protein as determined by in vitro chloroplast import and immunoblotting, Antibody to cpTatC specifically inhibited the thylakoid Delta pH-dependent pathway in vitro. cpTatC is present in about the same quantity as estimated translocation sites, whereas Hcf106 and Tha4 are present in 5-8-fold excess. These results are relevant to mechanistic models for this system. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.