Nucleotide sequences of the 2-oxoacid ferredoxin oxidoreductase and ferredoxin genes fromFrankiastrain EuIK1, a symbiont ofElaeagnus umbellataroot nodules

Abstract

A genomic clone, pEuNIFII, was isolated by screening a genomic library of Frankia strain EuIK1, a symbiont of Elaeagnus umbellata Thunb. root nodules. A 1.5-kb fragment of pEuNIF4.0, which contained ORF2 and N-terminal part of nifS, was used as a probe. A 7.2-kb BamHI fragment of pEuNIFII, which was proven to be adjacent to the probe, was subjected to sequence determination. The sequence analysis suggested one partial ORF followed by three open reading frames (ORFs). Two ORFs next to nifS encodes an a subunit (672 amino acids) and b subunit (347 amino acids) of a 2-oxoacid ferredoxin oxidoreducatase (OR), respectively. The third ORF encodes 114 amino acids of a 7Fe-type ferredoxin (Fdx). All ORFs are transcribed in the same direction as other nif genes. Alignment of the deduced amino acid sequences from frankiae OR revealed the motifs of gamma and alpha domains seen in other ORs in the a subunit, and the beta domain in the b subunit. Frankia or shows about 44% nucleotide sequence similarity with nifJ from Klebsiella pneumoniae, while frankiae fdx shows about 56% similarity with fdxI from Azotobacter vinelandii. These genes are reported for the first time in Frankia, and putative roles of their products in symbiosis is discussed in relation to nitrogen fixation and carbohydrate metabolism.Key words: 2-oxoacid ferredoxin oxidoreductase, ferredoxin, nucleotide sequence, Frankia EuIK1.