Summary: The gene () encoding an oxygen-labile fumarase of has been cloned and sequenced. The structural gene (1542 bp) encodes a product (FumA) of 56788 containing 514 amino acid residues. The amino acid sequence is 23% identical (37% similar) to FumA and FumB, the labile [4Fe–4S]-containing fumarases (Class I enzymes) of . It exhibits no significant similarity to FumC and CitG, the stable fumarases (Class II enzymes) of and (respectively). Enzymological studies indicated that FumA resembles the iron-sulphur-containing fumarases in being dimeric ( 2 × 58500), oxygen labile and partially reactivated by Fe plus DTT. The gene is the first gene encoding a Class I fumarase to be characterized in any organism other than . Enzymological and DNA-hybridization studies further indicated that resembles in containing an oxygen-stable fumarase (Class II enzyme). Sequence comparisons revealed significant similarities between the Class I fumarases and the products of adjacent open-reading frames ( and ) located upstream of the macromolecular synthesis operon (--) at 67 min in the linkage map. Located downstream of , there is an unidentified gene (), which is homologous to the rhizobial genes involved in the initiation of root nodule formation.


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