The gene encoding a ferredoxin (Fd) from Haloarculajaponica strain TR-1 was cloned and sequenced. Sequence analysis of the cloned Ha. japonica Fd gene revealed that the structural gene consisted of an open reading frame of 387 nucleotides encoding 129 amino acids. The deduced amino acid sequence of Ha. japonica Fd showed 84 to 98% identity with corresponding sequences in other extremely halophilic archaea. The Ha. japonica Fd gene was inserted into the shuttle vector pWL102 and used to transform Ha. japonica. Ha. japonica Fd could then be produced as a fusion with His-Tag (6xHis) in Ha. japonica host cells. The absorption and ESR spectra of the Fd/His Tag fusion protein revealed the presence of a [2Fe-2S] cluster which is characteristic of native Ha. japonica Fd.