Figure 1

Plasmid maps for the expression of proteorhodopsin in E. coli. Erwinia uredovora crt E, B, I, Y (for β-carotene synthesis), mouse β-diox gene (for conversion of β-carotene to retinal), and pR gene coding proteorhodopsin were cloned into pACYC-Duet1 vector to construct pACYC-RDS. All of the genes were amplified using the primers in Table 1 and digested using restriction enzymes for cloning into pACYC-Duet1. pET-HmH/pR was constructed by cloning a single pR gene into pET-HmH, which expresses H. marinus [NiFe]-hydrogenase, to investigate the function of proteorhodopsin with exogenous retinal. pACYC-pR (without crtE, B, I, Y, β-diox) was also constructed to measure the absorption spectrum of E. coli with membranes expressing proteorhodopsin (Figure 2B).