The removal of either the PsbU or PsbV protein has been investigated in a cyanobacterial ΔPsbO strain and in mutants carrying deletions or substitutions in lumen-exposed domains of CP47. These experiments have demonstrated a functional interaction between the PsbU protein and photosystem II (PSII) in the absence of the PsbO subunit. The control:ΔPsbO:ΔPsbU strain assembled PSII centers at pH 7.5 but did not evolve oxygen; however, photoautotrophic growth was restored at pH 10.0. In addition, several CP47 mutants, lacking extrinsic proteins, were obligate photoheterotrophs at pH 7.5 but photoautotrophic at pH 10.0, whereas other strains remained photoheterotrophs at alkaline pH.
