Characterization of a ferric uptake regulator (fur) gene from Xanthomonas campestris pv. phaseoli with unusual primary structure, genome organization, and expression patterns.

A 1.5kb DNA fragment from Xanthomonas campestris pv. phaseoli containing fur was characterized. fur is a single copy gene that is transcribed as a monocistronic mRNA. The predicted amino acid sequence of Xp Fur showed extensive identity to other Fur proteins. However, Xp Fur has many distinct features, particularly a lack of cysteine residues in the conserved metal-binding motifs and unusual modifications in the carboxy-terminus region. The nucleotide sequences of fur genes from four other Xanthomonas spp. were determined. Deduced amino acid sequences all showed the distinct features of Xp Fur. Functionally, Xp Fur partially repressed a Fur-regulated promoter in E. coli. Expression analysis of fur showed increased fur mRNA levels in response to a low iron growth condition. The fur transcription start site was identified by primer extension.