(B) Sox6 represses ɛy promoter activity in a dosage-dependent manner. In GM979 cells, the E-Luc ɛy promoter reporter construct was co-transfected (1) without overexpression of Sox6; (2–4) with increasing amounts of CMV-Sox6 overexpression vector; (5) with a truncated version of Sox6 that lacks its HMG domain; (6) with a mutant version of Sox6 (L386H) that has previously been shown to abolish interaction with CtBP2; or (7) with an empty reporter plasmid (without ɛy promoter and μLCR element).