The BTB/POZ domain containing the N-CoR interaction region is required for transcriptional repression by the PLZF protein. Cell transfections were performed in 6-well plates (∼10⁶ cells per well per transfection) using SuperFect reagent (Promega). (A) Increasing amounts (as indicated) of expression vectors for the wild-type PLZF and PLZF▵POZ (solid and open boxes, respectively) were cotransfected with L4-tkluc (400 ng) reporter vector and 50 ng of CMV-lacZ plasmid as a control for transfection efficiency. Results are expressed as the percentage of luciferase activity obtained in the presence of equivalent amounts of cotransfected empty expression vector (pSG5). (B) Cotransfection of PLZF (60 ng), N-CoR (300 ng), and Sin3A (300 ng). Expression plasmids were transfected in the indicated amounts and the percentage of L4-tkluc (400 ng) activity was evaluated as described in (B). (C) Addition of TSA (200 ng/mL), a histone deacetylase inhibitor, relieved repression of the L4-tkluc reporter plasmid expression by the PLZF protein. In this experiment, 300 ng of PLZF expression vector or empty vector (pSG5) control, together with 400 ng of L4-tkluc and 50 ng CMV-lacZ, were cotransfected.