Assembly of the PSII complex in Synechocystis sp. PCC 6803. Proposed scheme for the assembly of PSII based on the analysis of PSII assembly complexes in defined mutants and radioactive pulse–chase experiments. For clarity, assembly factors and many of the low molecular mass (LMM) sub-units are not included. The LMM PsbE, PsbF, PsbH, PsbI and PsbK sub-units and the extrinsic PsbO, PsbU and PsbV sub-units are designated by the appropriate upper case letter, and the small CAB-like proteins by SCPs. Cytochome b-559 (cyt b-559) is composed of a heterodimer of the PsbE and PsbF subunits. Types of PSII complex: RC, PSII reaction centre-like complexes containing either mature D1, intermediate D1 (iD1) or precursor D1 (pD1) but lacking CP47 and CP43; RC47, PSII core complexes lacking CP43; RCC1, monomeric PSII core complex; RCC2, dimeric PSII core complex. The site of attachment of the extrinsic proteins to PSII is purely illustrative.