Abstract
CP12 in photosynthetic organisms contained four Cys essential for formation of N-terminal and C-terminal peptide loops to interact with PRK and GAPDH proteins. However, CP12 in Synechococcus PCC7942 lacked two Cys to form the N-terminal peptide loop. The mutant CP12 changed Cys-61 and Cys-70 to Ser involved in formation of the C-terminal peptide loop had no effect on CP12/PRK interaction, suggesting that the N-terminal region of CP12 is associated with the interaction with PRK in spite of absence of two Cys. The growth rate of CP12-disrupted mutant (ScΔCP12) was almost the same as that of wild-type under continuous light conditions. However, under 12-h light/12-h dark conditions, ScΔCP12 cells grew significantly slower than wild-type cells. In the dark, RuBP content in the ScΔCP12 cells was significantly larger than that in wild-type cells. These data suggest that the CP12 in cyanobacteria is associated with regulation of the Calvin cycle in the dark.
