CHLOROPHYLL IN A SYNECHOCYSTIS SP PCC-6803 MUTANT WITHOUT PHOTOSYSTEM-I AND PHOTOSYSTEM-II CORE COMPLEXES - EVIDENCE FOR PERIPHERAL ANTENNACHLOROPHYLLS IN CYANOBACTERIA

The chlorophyll protein organization has been investigated in thylakoi d membranes from mutants of the cyanobacterium Synechocystis sp. PCC 6 803, in which the photosystem II (PS II) genes psbB and/or psbC (codin g for CP47 and CP43, respectively) were inactivated together with the psaAB operon (coding for the photosystem I (PS I) core complex) and th e apcE gene (coding for the phycobilisome anchor protein). Lack of the CP43 protein led to a significant decrease of the D1, D2, and CP47 pr oteins and a decrease in the 77 K fluorescence emission peak at 685 nm . In the absence of the CP47 protein, no PS II reaction center assembl y was detected and the 77 K fluorescence emission peak at 695 nm was l ost. The psbB(-)/psbC(-)/PS I-less/apcE(-) mutant had no assembly of t he D1, D2, CP47, and CP43 proteins, had lost the 77 K fluorescence emi ssion peaks at 685 and 695 nm, but retained about 15% of the chlorophy ll present in the PS I-less/apcE(-) background strain. A broad 77 K fl uorescence emission band with a maximum at 678 nm was displayed in the PS II-less, PS I-less mutant upon excitation of the remaining chlorop hyll. A 678 nm shoulder was observed in the 77 K fluorescence emission spectrum of thylakoids from the psbB(-)/PS I-less/apcE(-) mutant, whi ch still contains CP43 but no PS LI reaction center. This shoulder was absent in thylakoids from the psbC(-)/PS I-less/apcE(-) mutant, which contain some PS II reaction center complexes. These results are consi stent with the chlorophyll associated with the 678 nm emission to serv e as peripheral antenna to PS II. The fluorescence emission characteri stics of this chlorophyll are different from those of an accessory chl orophyll-binding protein expressed under iron-stress conditions in cya nobacteria. The chlorophyll remaining in the absence of PS II and PS I is indicative of a new chlorophyll binding protein in cyanobacterial thylakoids.