A regulatory gene, angR, of the iron uptake system of Vibrio anguillarum: similarity with phage P22 cro and regulation by iron

The angR locus in Vibrio anguillarum encodes a trans-acting transcriptional activator which modulates several Fe²⁺ -regulated loci in the anguibactin biosynthesis gene cluster. In this paper, the complete nucleotide (nt) sequence of the angR gene and deduced amino acid (aa) sequence of the AngR protein are presented. A region upstream from the angR gene is shown to have similarity with Fe²⁺- regulated operators in Escherichia coli which bind the Fur protein. The involvement of a Fur-like regulator is supported by transcription analysis which show that angR itself is Fe²⁺- regulated. The aa sequence of the AngR protein predicts a helix-turn-helix motif which shows striking homology with prokaryotic DNA-binding proteins, particularly the λ and P22 Cro proteins. In addition, there are two 18-nt regions, upstream from the angR gene, which show similarity with the o_R1 and o_R2 operators of P22 cro. These regions overlap with, respectively, the -35, -10 region and the putative Fur-binding region upstream from angR. These results suggest that AngR may be a DNA-binding protein which modulates Fe²⁺- regulated transcription and is itself Fe²⁺- regulated at the transcriptional level.