Targeting signals for a bacterial Sec‐independent export system direct plant thylakoid import by the ΔpH pathway

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Abstract
Preproteins targeted to the Sec‐independent protein transport systems of plant thylakoids and of bacteria both have unusual transfer peptides bearing a consensus twin‐arginine motif. Possible mechanistic similarity between the two Sec‐independent transport pathways was investigated by assessing the ability of bacterial twin‐arginine transfer peptides to direct thylakoid import. High efficiency import was observed. This process was demonstrated to occur specifically via the Sec‐independent ΔpH pathway and to depend on an intact twin‐arginine motif on the transfer peptide. These results provide strong evidence for the operation of mechanistically related Sec‐independent protein transport pathways in chloroplasts and bacteria.