CXXC domain and flanking regions of MLL are responsible for RUNX1 downregulation. (A) Schematic representations of the major domains of MLL, the C-terminal truncation and internal deletion constructs, and the CXXC domain constructs of MLL1 (1137-1211 aa), MLL2/KMT2B (948-1022 aa), and CGBP (150-225 aa) generated for studying the MLL domains that were responsible for RUNX1 downregulation. (B-D) RUNX1 were cotransfected with blank vector, full-length MLL, or constructs indicated in panel A in 293T cells. At 40 hours’ posttransfection, whole cell lysates were analyzed for expression of RUNX1 and MLL or MLL deletions. β-Actin was used as a loading control. All of these experiments were repeated 3 times and representative data are shown.