Complementation of bacterial SecE by a chloroplastic homologue

The SecE protein is an essential component of the SecAYE-translocase, which mediates protein translocation across the cytoplasmic membrane in bacteria . In the thylakoid membranes of chloroplasts, a protein homologous to SecE, chloroplastic (cp) SecE, has been identified, However, the functional role of cpSecE has not been established experimentally, In this report me show that cpSecE in cells depleted for bacterial SecE (i) supports growth, (ii) stabilizes, just like bacterial SecE, the Sec-translocase core component Se cY, and (iii) supports Sec-dependent protein translocation, This indicates that cpSecE can functionally replace bacterial SecE in vivo, and strongly s uggests that the thylakoid membrane contains a SecAYE-like translocase with functional and structural similarities to the bacterial complex. This stud y further underscores the evolutionary link between chloroplasts and bacter ia. (C) 2001 Federation of European Biochemical Societies. Published by Els evier Science B.V. All rights reserved.