Figure 3.

Luciferase assays indicate that both X. tropicalis TRα (A) and TRβ (B) can repress and activate the activity of the T₃-inducible promoter of X. laevis TRβA gene and RXR enhances the activities. X. laevis oocytes were injected into the cytoplasm with mRNAs encoding indicated proteins. Subsequently the reporter vector with the firefly luciferase under the control of the T₃-inducible promoter of X. laevis TRβA gene and phRG-Tk Renilla luciferase control vector were coinjected into the nucleus of the oocytes. The oocytes were then incubated with or without T₃ before harvesting for luciferase assays. The ratio of the reporter firefly luciferase activity to the control Renilla luciferase activity was plotted (top panels). Western blot analysis was also done on the same the lysate with anti-FLAG antibody, demonstrating the expression of the FLAG-tagged TRα and TRβ (bottom panels). In a separate experiment using mRNA encoding FLAG-tagged RXRβ, Western blot analysis with the anti-FLAG antibody showed the expected expression of RXRβ in the injected oocytes (data not shown).