Fig. 1: Simple model of the initial stages of assembly of PSII and the various isolated RCII complexes.

The D1 module contains precursor D1 (pD1), PsbI (I) and Ycf48 (Y48) and the D2 module contains D2, the PsbE (E) and PsbF (F) subunits of Cyt b-559 and CyanoP (P). Precursor D1 is cleaved to intermediate D1 (iD1) and mature D1 upon formation of the RCII complexes, RCIIa and RCII*. RCII* is equivalent to RCIIa but additionally contains the Ycf39 (Y39)/Hlips (High light inducible proteins) complex. The Hlips complex (HliCD) consists of the HliC and HliD subunits. The rubredoxin-like RubA protein is found in RCIIa and RCII*. The His-tagged RCII/PSI complex studied here was purified by immobilised Ni2+-affinity chromatography followed by sucrose density gradient centrifugation. Only the large PsaA and PsaB RC subunits are displayed in PSI for clarity.