PARENT SESSION
Posters P6A Type II reaction centres: Excited state dynamics and donor side. Abstracts (313-346)

A combined D1 (PsbA) and CP47 (PsbB) mutagenesis system in Synechocystis sp. PCC 6803. Regan Winter^*,1, William Nicoll¹, Julian Eaton-Rye¹, ¹ Department of Biochemistry, Dunedin, New Zealand

ABSTRACT- A cyanobacterial mutagenesis system has been constructed in Synechocystis sp. PCC 6803 to study protein interactions of Photosystem II (PSII) that involve the reaction centre protein D1 (PsbA) and the chlorophyll a-binding protein CP47 (PsbB). The psbA1 and psbA3 genes have been deleted in this system and mutations incorporated into psbA2 and psbB: thus amino acid deletions and substitutions can be introduced into D1 and CP47 within the same strain for in vivo studies. Using this system the D1 substitutions of Ser-101 to Ala and Thr-292 to Leu were combined with the replacement of Glu 364 by Gln in CP47 and a deletion between Arg-384 and Val-392 in CP47. Photoautotrophic growth and oxygen evolution in the D1:S101A, D1:T292L and CP47:E364Q strains were similar to wild type (photoautotrophic doubling time 12 h) and the CP47:(R384-V392) mutant exhibited oxygen evolution rates 55% of wild type, while also retaining a photoautotrophic doubling time of 12 h. However, the S101A:E364Q and T292L:E364Q mutants had oxygen evolution rates comparable to those of wild type but exhibited reduced photoautotrophic growth (doubling time 20 h), whereas the S101A:(R384-V392) and T292L:(R384-V392) strains also exhibited reduced photoautotrophic growth rates (doubling time 20 h) but evolved oxygen at rates 40% of wild type. These results illustrate that this system can be used to test functionally important interactions between PSII proteins, and we are actively investigating further combined mutants in D1 and CP47.

KEY WORDS: cyanobacteria, PSII, Synechocystis, mutagenesis