Co(III)-Ci irreversibly binds to the Ci zinc finger domain. (A) Lane 1. 10 nM 32P radiolabeled Co(III)-Ci. Lane 2. 10 nM 32P radiolabeled Co(III)-Ci incubated with control S2 extracts not expressing the Ci zinc finger domain. The Ci zinc finger domain was overexpressed in S2 cells, cells were lysed and incubated for 3 hours with either 1X 32P radiolabeled Co(III)-Ci (lanes 3 and 4), 10 nM 32P radiolabeled Co(III)-CiMut (lanes 5 and 6) or 32P radiolabeled Ci probe (lanes 8 and 9). Then either buffer (A, lanes 3, 5 and 8) or 150X cold competitor (lanes 4, 6 and 9) was added to reactions for 15 minutes. Reactions were analyzed by EMSA on a 4% TBE/acrylamide gel and performed in triplicate. Representative gels are shown. (B) EMSAs were quantified using ImageQuant software. Error bars are one standard deviation. Final reaction concentrations are given.