IMPORT OF MODIFIED D1 PROTEIN AND ITS ASSEMBLY INTO PHOTOSYSTEM-II BYISOLATED-CHLOROPLASTS

A portion of the rbcS gene that encoded the transit peptide and 20 ami no acid residues of the N-terminal region of the small subunit of ribu losebisphosphate carboxylase/oxygenase was fused to the 5' end of the psbA gene which encodes the D1 protein of PSII reaction center, The ch imeric gene was expressed in vitro as a 42-kDa protein, which was impo rted into chloroplasts isolated from pea leaves. The imported protein was processed such that the transit peptide was lost in the stroma, th e resultant protein was translocated into thylakoid membranes, and the C-terminal peptide was then removed to yield a mature protein with an N-terminal extension originated from the small subunit, The mature pr otein appeared to be assembled into the PSII core complex, resembling the native DI protein in terms of protein structure and topology withi n the membrane. Our observations indicate that the structure of the pr ecursor to the D1 protein includes information for the proper assembly of the protein into the PSII core complex.