FIG. 5.

Homodimerization and XRE binding activities of the bHLH domain of the dioxin receptor. (A) In vitro-translated full-length dioxin receptor was labeled with [³⁵S]methionine incubated with 0.1 μg of the indicated dioxin receptor fusion proteins, precipitated with glutathione-Sepharose, and analyzed by SDS-PAGE and fluorography. (B) Homodimerization activity of the minimal DR-1-82 receptor fragment was monitored in vivo by using a mammalian two-hybrid assay. COS-7 cells were cotransfected with 0.2 μg of pCMX DR-1-82–Gal4 containing the dioxin receptor bHLH domain fused to the Gal4 DNA binding domain and up to 100 ng of a DR-1-82–VP16 fusion construct together with 0.5 μg of a Gal4 luciferase reporter construct. The cells were assayed for luciferase activity, and results of a representative experiment are shown.