Abstract
Two different types of glutamate synthase, Fd- and NADH-GOGAT, are present in a cyanobacteria Plectonema boryanum. Analysis of mutants lacking either GOGAT genes has indicated that Fd-GOGAT plays a major role in balancing of N and C photoassimilation. Here, we analyzed regulation of Fd-GOGAT in both protein and gene levels in terms of C/N balancing. After shifting the culture condition for C-assimilation from a low to high levels, the amount of Fd-GOGAT increased significantly in P. boryanum, while NADH-GOGAT was constant. No such response was found for other nitrogen assimilation enzyme, such as nitrite reductase. The same phenomena were observed in Synechocystis PCC6803. Using P. boryanum cells transformed with luciferase gene under regulation of Fd-GOGAT gene promoter, we observed a rapid up/down-regulation of the promoter in response to C-assimilation status. We are now analyzing this promoter activity in more details.
