Cytochrome f encoded by the chloroplast genome is imported into thylakoids via the SecA-dependent pathway

In vitro import of the precursor of tobacco cytochrome f, which is is encoded by the chloroplast genome, into isolated pea thylakoids was analyzed. Upon incubation with thylakoids and a stromal fraction, the precursor of cytochrome f was efficiently imported into thylakoids. The imported cytochrome f was tightly integrated into the thylakoid membrane. Insertion of cytochrome f into the thylakoid membrane was blocked by nigericin, sodium azide, and antibodies against pea chloroplast SecA. These results suggest that cytochrome f utilizes the bacterial-type SecA-dependent pathway to be imported into thylakoids.