The manganese stabilizing protein (MSP) and the control of O-2 evolution in the unicellular, diazotrophic cyanobacterium, Cyanothece sp ATCC 51142

The unicellular diazotrophic cyanobacterium, Cyanothece sp. ATCC 51142 temp orary separates N-2 fixation from photosynthesis. To better understand the processes by which photosynthesis is regulated, we have analyzed Photosyste m (PS) II O-2 evolution and the PSII lumenal proteins, especially the Mn st abilizing protein (MSP). We describe a procedure using glycine betaine to i solate photosynthetic membranes from Cyanothece sp, that have high rates of PSI and PSII activity. Analysis with these membranes demonstrated similar patterns of O-2 evolution in vivo and in vitro, with a trough at the time o f maximal N-2 fixation and with a peak in the late light period. The patter n of PSI activity was also similar in vivo and in vitro. We cloned the gene s for MSP (psbO) and the 12 kDa protein (psbU) and analyzed their transcrip tional properties throughout the diurnal cycle. We suggest that the changes in PSII activity in Cyanothece sp. were due to conformational changes in a highly flexible MSP, a suggestion which can now be studied in a chimera. T he Cyanothece sp. psbO gene has been transformed into Synechocystis sp. PCC 6803; MSP and O-2 evolution in the resulting transformant had properties t hat were similar to those in Cyanothece sp., providing additional confirmat ion for the properties of Cyanothece sp. MSP. (C) 2001 Elsevier Science B.V . All rights reserved.