SEQUENCING AND COMPLEMENTATION ANALYSIS OF THE NIFUSV GENES FROM AZOSPIRILLUM-BRASILENSE

The functionality of nitrogenase in diazotrophic bacteria is dependent upon nif genes genes other than the structural nifH, D, and K genes w hich encode the enzyme subunit proteins. Such genes are involved in th e activation of nif gene gene expression, maturation of subunit protei ns, cofactor biosynthesis, and electron transport. In this work, appro ximately 5500 base pairs located within the major nif gene cluster of Azospirillum bransilense Sp7 have been sequenced. The deduced open rea ding frames were compared to the nif gene products of Azotobacter vine landii and other diazotrophs. This analysis indicates the presence of five ORFs encoding ORF2, nifU, nifS, nifV, and ORF4 in the same sequen tial organization as found in other organisms. Consensus sigma(54) and NifA binding sites are present in the putative promoter region upstre am of ORF2 in the A. brasilense sequence. The nifV gene of A. brasilen se but not nifU or nifS complemented corresponding mutants strains of A. vinelandii. (C) 1998 Federation of European Microbiological Societi es. Published by Elsevier Science B.V.