SPECIFIC REQUIREMENTS FOR CYTOCHROME C-550 AND THE MANGANESE-STABILIZING PROTEIN IN PHOTOAUTOTROPHIC STRAINS OF SYNECHOCYSTIS SP. PCC-6803 WITH MUTATIONS IN THE DOMAIN GLY-351 TO THR-436 OF THE CHLOROPHYLL-BINDING PROTEIN CP47

The requirement of cytochrome c-550 (PSII-V) in photosystem II (PSII) has been assessed in Synechocystis sp. PCC 6803 containing mutations b etween Gly-351 and Thr-436 of the loop E domain of the chlorophyll a-b inding protein CP47. Six photoautotrophic strains were utilized to com pare the effect of removal of either the manganese-stabilizing protein (PSII-O) or PSII-V on PSII activity in vivo. These were a wild-type c ontrol; two strains with amino acid deletions, Delta(R384-V392) and De lta(G429-T436); and three carrying specific amino acid substitutions, G351L/T365Q, G351U/E364Q/T365Q, and G351L/E353Q/E355Q/T365Q. The remov al of PSII-O prevented the assembly of PSII in Delta(G429-T436) but no t in Delta(R384-V392). Neither Delta(G429-T436) nor Delta(R384-V392) c ould support photoautotrophic growth in the absence of PSII-V. In chlo ride-limiting conditions, the photoautotrophic growth of Delta(R384-V3 92) was severely impaired and that of Delta(G429-T436) totally inhibit ed, and no strains lacking PSTI-V could grow in chloride-limiting or c alcium-limiting media. Substitutions at Gly-351, Glu-353, Glu-355, and Thr-365 produced phenotypes that were similar to those of the control in the presence or absence of PSII-O and PSII-V, but removal of PSII- O from G351L/E364Q/T365Q produced a significant reduction of assembled PSII centers and an enhanced sensitivity to photoinactivation while r emoval of PSII-V prevented photoautotrophic growth. The additional mut ants E364Q:Delta PSII-V and E364G:Delta PSII-V demonstrated that this inhibition was a consequence of the mutation at Glu-364. These results also show that the removal of PSII-V, in vivo, produces phenotypes in the CP47 mutants examined that are either similar or more severe than those resulting from the removal of PSII-O.