Trace metals are essential for life. Organisms must obtain sufficient quantities of trace metals for growth, while preventing the accumulation of excess metal which can be toxic to the cell. Our laboratory is interested in understanding the regulation of cellular metal uptake, and we have begun our studies by investigating Ni uptake in E. coli. Here, nickel concentrations are controlled by transcriptional repression of the nickel-specific ABC transporter. In the presence of excess intracellular nickel, the nickel-dependent repressor NikR binds to an operator sequence, turning off expression of the transporter and decreasing nickel import. To gain insight into how nickel regulates NikR function, we are determining crystal structures apo NikR, nickel-bound NikR by itself, and the NikR:DNA complex.