Abstract
The reported crystallographic structural model of cyanobacterial PS II suggests important function of PsbU in water oxidation. We have deleted the psbU gene in Synechocystis 6803. The &DeltapsbU cells could not grow if both of Ca2+ and Cl- were eliminated from the growth medium. The light utilization efficiency and the maximum rate of oxygen evolution were highly reduced than in wild type cells even if after grown in normal BG11. S2-state decay was slowed down, whereas S3-state showed faster decay in &DeltapsbU. The S-state distribution after dark adaptation was also perturbed. Polypeptide analysis showed that a number of extrinsic proteins (PsbO, PsbV and PsbQ) were absent in the isolated &DeltapsbU PS II complex. These results supports the idea that PsbU contributes to the functional assembly of the extrinsic proteins and Ca2+ ion to assist efficient water oxidation in PS II.
