Fig. 4. Working model showing the genomic organization of uipRS and A genes, and the proposed mechanism of U sensing and the function of UipA.

The topology of UipS was predicted using the CCTOP program. UipS is predicted to be a histidine kinase, which could be involved in Fe and U sensing and activation of its cognate regulator, UipR (REC = receiver domain; HTH = Helix Turn Helix domain), via phosphate transfer. The activated UipR would then induce uipA gene expression, leading to overproduction of the protein UipA, formation of UipA dimers at the cell surface, and metal binding. Hypothetical functions of UipA are proposed.