REGULATION OF THE TRANSCRIPTIONAL ACTIVATORS ANFA AND VNFA BY METALS AND AMMONIUM IN AZOTOBACTER-VINELANDII

Transcription of the genes encoding molybdenum (Mo)-independent nitrog enases 2 and 3 of Azotobacter vinelandii requires the activators VnfA and AnfA, respectively. The effect of NH4+, Mo, or V (vanadium) was te sted on the expression of vnfA-lacZ and anfA-lacZ transcriptional fusi ons. Mo repressed expression of both fusions whereas NH4+ and V repres sed the anfA-lacZ fusion, but not the vnfA-lacZ fusion. Thus the repre ssive effect on transcription of the anfHDGKOR operon by NH4+, Mo, or V is mediated through their effect on transcription of anfA and the re pressive effect of Mo on the vnfHFd and vnfDGK operons is mediated thr ough Mo repression of vnfA transcription. Mo-dependent repression of a nfA transcription is influenced but not entirely mediated by the Mo-re sponsive regulator ModE. (C) 1998 Federation ol European Microbiologic al Societies. Published by Elsevier Science B.V. All rights reserved.