Replacing the HMG box of Sox9 abolished the inhibitory effect of Exp4 on Sox9 transcription.

<p>(A) Schematic representation of GAL4-fused Sox proteins (GAL4-Sox9) used in this study. The TA domain is shown as a light gray box (406–507 a.a.). (B) The effect of Exp4 on Sox9-mediated transcription of the Col2a1 reporter gene (Col2a1x3-tk-Luc). HEK293 cells were transiently transfected with the reporter gene and the indicated amounts (ng) of Sox9 or Exp4. The relative fold changes in the luciferase activities are shown: luciferase activity in the presence of 50 ng of Sox9 and the absence of Exp4 is set at 100. Values are the mean ± SD of at least three experiments. (C) The effect of Exp4 on GAL4-Sox9 mediated transcription of the GAL4 reporter gene (UAS_Gx4-TK-LUC). HEK293 cells were transiently transfected with the reporter gene and the indicated amounts (ng) of GAL4-Sox9 or Exp4. The relative fold changes in the luciferase activities are shown: luciferase activity in the presence of 50 ng of GAL4-Sox9 and the absence of Exp4 is set at 100. Values are the mean ± SD of at least three experiments.