THE FDX GENE ENCODING THE [2FE-2S] FERREDOXIN OF HALOBACTERIUM-SALINARIUM (H-HALOBIUM)

The gene encoding the [2Fe-2S] ferredoxin (fdx gene) was isolated from Halobacterium salinarium using two oligonucleotides deduced from the ferredoxin sequence as probes. Cosmid DNAs exhibiting hybridization we re isolated, the fdx gene was localized to smaller subfragments and th e nucleotide sequence determined. The 390 bp coding sequence is locate d in the halobacterial FI-DNA and transcribed as a 440 nucleotide mRNA . S1 mapping indicated that the 5' terminus of the mRNA maps immediate ly upstream of the ATG start codon. The promoter box A, centred around position -25 (5' AC-TATG 3'), and box B (TG) elements at the start of the transcript resemble the sequences of a typical archaeal promoter. The restriction pattern of an approximately 50 kb region surrounding the fdx gene is conserved in various Halobacterium species. The haloba cterial ferredoxin and the major gas vesicle protein GvpA exhibit up t o 70% similarity to their respective counterparts in cyanobacteria sug gesting lateral gene transfer between the organisms. These similaritie s prompted a more detailed investigation of the relative positions of the genes in the halobacterial genome.