RB1 and urea cycle disorder: To test whether the ATP-dependent chromatin-remodeling activity of Brm1 is required for the transient association of RB and HP1β to chromatin, we transfected an empty vector control, a dominant negative, ATPase-dead Brm1 (dnBRM1) mutant that lacks chromatin-remodeling activity (Bourachot et al., 1999) or dnBrm1 plus Brg1, in UCD-HDAC1 cells before or after induction of HDAC1 for 2 days.