Grgs repress Sox2 transcriptional activation activity. Co-transfected Sox2 caused an approximately 2-fold increase in luciferase activity from the 3xSX promoter (A) or 25-fold increase from the REX promoter (B) in Cos-7 cells, but this increase was significantly inhibited when Grg3 or Grg5 were co-transfected (A,B). (C) Co-expression of Sox2 with the GFAP-luciferase reporter construct in P19 cells caused a 2-fold decrease in luciferase activity compared to vector alone and the presence of either Grg3 or Grg5 increased this repression (although the difference was only significant in the presence of Grg3). (D) Cotransfected Grg3 or Grg5 caused no significant difference from controls (vector) in luciferase activity from various promoters in P19 cells. *p = <0.05; **p = <0.01.