Study on the Auto-assembly of Truncated Phytochrome from Synechocystis sp.PCC7120

Five truncated fragments of aphA gene were amplified from the genomic DNA of Synechocystis sp.PCC7120 by PCR,including aphA(26-320),aphA(27-320),aphA(28-320),aphA(29-320)and aphA(32-320).After expression via the vector pET30,reconstitutions of the expressed mutated apo-proteins with phycocyanobilin(PCB) were studied in vitro under certain conditions.The results showed:The chromoprotein that obtained from the reconstitution of AphA(26-320) had similar photochemical properties of plant phytochrome.The covalent binding of PCB with the chromoprotein was verified further by acid-urea denaturation and UV-induced fluorescence by Zn²⁺-SDS gel tests.The maximal Pr/Pfr absorption of AphA(26-320) was at 660/610 nm.The other four truncated fragments,AphA(27-320),AphA(28-320),AphA(29-320),AphA(32-320) could not auto-assembly with PCB in the similar conditions,as no reversible photochemistry was detected.The results implicates that the lyase domain of AphA existing in AphA(26-320).