Fig. 5. T. gondii infection results in different levels of NF-B DNA binding activity depending on the IKK background of the host cell. (A) Binding reactions for EMSA were performed with a radiolabeled oligonucleotide probe containing the NF-B consensus sequence and nuclear protein extracts from uninfected (U) or infected (I) cells. Diverse NF-B binding activities of three complexes (C1, C2 and C3) are observed among WT, IKK^–/–, IKKß^–/– and IKK^–/–ß^–/– cells with infection. Increases in binding activity of complexes C2 and C3 are observed in infected WT and, to a lesser extent, in IKK^–/– cells compared with uninfected controls (dashed box). Levels of NF-B binding activity of C2 and C3 complexes are minimal in infected IKKß^–/– cells and absent in infected IKK^–/–ß^–/– cells. (B) Supershift analysis of infected WT, IKK^–/– and IKKß^–/– cells determined the presence of p50/p65 and p50/p50 dimers in the C2 and C3 complexes, respectively (arrowheads). The disappearance or marked reduction of C1 with the p50 but not the p65 antibody suggests the presence of p50 subunits in this complex, which might also consist of additional unidentified proteins.