Abstract
Action of the carboxyl-terminal processing protease (CtpA) is indispensable for appearance of oxygenic photosynthetic competence. As an approach for molecular dissection of this essential protease, we constructed an in vivo assay system for activity of mutagenized CtpA. In this system, spinach CtpA gene was transformed into a Synechocystis heterotrophic mutant deficient in its native ctpA gene. The transformant with WT spinach CtpA regains photoautotrophic growth competence, suggesting that the spinach CtpA is replaceable with the host ctpA in Synechosystis cells. Next, we introduced the mutant CtpA library in which codon for a selected residue was substituted randomly, into the system. Transformants were screened for autotrophy. The surviving cells under the condition certainly have an active CtpA gene and we sequenced the gene to elucidate codon at the residue. Variability of observed codons is likely to be a reciprocal factor to indicate importance of the residue on the CtpA action.
