Fig. 5. HDAC activity is altered in Arnt-null TS cells. (A) Differentiation of wild-type TS cells was associated with increased levels of acetylated H4 (Ac-H4). A similar increase was observed during differentiation of the Arnt-null TS cells, although baseline levels in the undifferentiated state were much higher than those observed in wild-type cells. HDAC1 expression, which does not change during differentiation, was used as a loading control. (B) Compensatory upregulation of multiple HDACs was observed in whole-cell lysates prepared from undifferentiated Arnt-null TS cells. (C) Analysis of nuclear extracts revealed altered translocation of multiple HDACs in mutant TS cells.