Figure 6.—

Expression of an ectopic copy of the CCDA gene partially suppresses ccs4. The ccs4-F2D8 arg7-8 strain was transformed with pSL18 (ccs4), pSL18 expressing the full-length CCS4 coding sequence (CCS4, ORF1), and pSL18 expressing the CCDA ORF (CCDA↑, transformants #a and #b₁) or cotransformed with pSL18 and the CCDA cDNA cloned (without promoter and terminator sequences) in pBluescript (CCDA↑, transformant #b₂). (A) Expression of an ectopic copy of CCDA partially restores the phototrophic growth of ccs4. Ten-fold dilution series were plated on acetate (heterotrophic conditions, 20 μmol/m²/sec of light) and minimal medium (phototrophic conditions, 300 μmol/m²/sec of light) and incubated at 25° for 1 and 3 weeks, respectively. (B) Fluorescence kinetics indicate partial restoration of cytochrome b₆f in ccs4 expressing an ectopic copy of CCDA. Fluorescence induction and decay kinetics were measured as described in Figure 1B. (C) Holocytochrome f accumulation is partially restored in the ccs4 mutant expressing an ectopic copy of CCDA. Strains were analyzed for cytochrome f accumulation by heme stain and immunoblot. Experimental conditions are the same as described in Figure 2C.