The protein assembly and stability of photosystem II (PSII) (sub)complexes were studied inmature leaves of four plastid mutants of tobacco (Nicotiana tabacumL), each havingone of thepsbEFLJoperon genes inactivated. In the absence of psbL, no PSII core dimers or PSII–light harvesting complex (LHCII) supercomplexes were formed, and the assembly of CP43 into PSII core monomers was extremely labile. The assembly of CP43 intoPSII coremonomers was found to be necessary for the assembly of PsbO on the lumenal side of PSII. .
