Evidence for SecA- and delta pH-independent insertion of D1 into thylakoids.

Many nuclear-encoded proteins are targeted into chloroplast thylakoids by an azide sensitive Sec-related mechanism or by a delta pH-driven mechanism. In this report, the requirements for the integration of chloroplast-encoded thylakoid proteins have been analysed in pulse-labeled intact chloroplasts. We show that the integration of the photosystem II reaction centre protein, D1, continues in the absence of a delta pH and in the presence of azide. A range of other proteins are similarly targeted to thylakoids in the presence of azide, suggesting that the SecA-related mechanism is not widely used for the targeting of chloroplast-encoded proteins.