The GS-GOGAT pathway is not operative in the heterocysts. Cloning and expression of glsF gene from the cyanobacterium Anabaena sp PCC 7120

The gene encoding the ferredoxin-dependent glutamate synthase (Fd-GOCAT), g lsF, from the heterocyst-forming cyanobacterium Anabaena so. PCC 7120, has been cloned and sequenced. Unlike other cyanobacteria, Anabaena 7120 contai ns only Fd-GOGAT, lacking NADH-GOGAT. The amount of glsF transcript and Fd- GOGAT activity were similar under all the nitrogen growth conditions tested , Enzyme activity, Western and Northern blot analyses indicated that Fd-GOG AT is absent in the heterocysts, while glutamine synthetase (GS) and NADP-i socitrate dehydrogenase (IDH) were present in these specialised cells. Our results clearly indicate that the GS-GOGAT pathway is not operative in the heterocysts, and hence glutamate must be imported from the adjacent vegetat ive cells, to sustain CS activity. Heterocysts probably export glutamine or another nitrogen rich compound like arginine to the vegetative cells. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Sc ience B.V. All rights reserved.