Nucleotide sequences of the 2-oxoacid ferredoxin oxidoreductase and ferredoxin genes from Frankia strain EuIK1, a symbiont of Elaeagnus umbellata root nodules

A genomic clone, pEuNIFII, was isolated by screening a genomic library of F rankia 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 o f 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 determinatio n. The sequence analysis suggested one partial ORF followed by three open r eading 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 oxidoredu catase (OR), respectively. The third ORF encodes 114 amino acids of a 7Fe-t ype ferredoxin (Fdx). All ORFs are transcribed in the same direction as oth er nif genes. Alignment of the deduced amino acid sequences from frankiae O R 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 fdr shows about 56% similarity with fdxI from Azotobacter vineland ii. These genes are reported for the first time in Frankia, and putative ro les of their products in symbiosis is discussed in relation to nitrogen fix ation and carbohydrate metabolism.