FIG. 4.

Membrane association and localization of band 7 proteins of Synechocystis sp. strain PCC 6803. (A) Differential membrane protein extraction from Synechocystis sp. strain PCC 6803 GT crude membrane isolations. After two consecutive freeze-thaw cycles (30 min at −80°C and 20 min at RT) in the indicated buffers (EB, 20 mM Tricine, pH 8.0; EB with 2 M NaCl; or 20 mM CAPS, pH 12.0), soluble (S) and pellet (P) fractions were generated by ultracentrifugation. An amount corresponding to 1 μg of Chl a was loaded per lane. The arrowhead indicates the antibody signal that corresponds to the Sll0815 protein. (B) Purified thylakoid membrane (TM) and plasma membrane (PM) fractions were generated by aqueous polymer two-phase partitioning, and 5 μg of protein was loaded in each lane. All samples in panels A and B were analyzed by 1-D SDS PAGE followed by immunoblotting with the indicated antibodies. (A) PsbO and D1 were used as markers for peripheral and integral membrane proteins, respectively. (B) CP43 and SbtA were used as markers for the purity of the thylakoid and plasma membrane fractions, respectively.