ATP-dependent import of a lumenal protein by isolated thylakoid vesicles

The 33 kd protein of the photosynthetic oxygen-evolving complex is synthesized in the cytoplasm as a larger precursor and transported into the thylakoid lumen via a stromal intermediate form. In this report we describe a reconstituted system in which the later stages of this import pathway can be studied in isolation. We demonstrate import of the 33 kd protein, probably as the intermediate form, into isolated pea thylakoids by a mechanism which is stimulated by the addition of ATP. The imported protein is processed to the mature size and is resistant to digestion by proteases. The thylakoidal protein transport system is specific in that non-chloroplast proteins and precursors of stromal proteins are not imported.