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

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