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IPTG(-/+) = without/with 0.2 mM IPTG for 3-6 hours, adding IPTG to a bacteria culture with OD600 0.2-0.3. M: Protein molecular weight marker ladder. Lane 2～10、13～15: pET28 plasmids encoding crtIEB separated by self-cleaving ribozyme, crtI+crtB+crtE, crtI&crtB&crtE，crtB+crtE+crtY，crtY，crtB without any tag were transformed into BL21(DE3) Rosetta strain, single clones(IEB4,IEB5,IEB6,I7,B1,E1,BEY2,Y1,B1)were picked for liquid LB culture. Lane 11~12: pET28 plasmids encoding crtBE separated by self-cleaving ribozyme without any tag were transformed into BL21(DE3) Hi-control Rosetta strain, single clones(BE12)were picked for liquid LB culture.

Protein expression was induced in parallel cultures by IPTG. Bacterial cultures were monitored by OD600, and 5x10^7 cells were harvested by centrifugation and lysis in 1x SDS sample buffer. Equal amount (10 μL, 2x10^6 cells) of whole cell lysate were analyzed by SDS-PAGE (14% separation gel).