Figure 1. Ash2L/RbBP5 stimulates MLL1 activity in the absence of WDR5.

(A) In vitro HMT assay for MLL1^SET and MLL1^SET with one, two or three components of the MLL1 complex as indicated on top. For all reactions, 5 µM of MLL1^SET was used and all other MLL1 core components were added at equal molar concentration. (B) Scintillation count for in vitro HMT assays using either four-component complex MWAR or three-component mixture MAR as enzymes. Y-axis, scintillation counts (cpm) for the methylation reaction. X-axis, molar concentration of MLL1^SET used in different reactions. Other proteins were added at equal molar concentration to MLL1^SET in each reaction. All experiments were repeated for three times. The error bar represented standard deviation. (C) In vitro HMT assay using various Ash2L fragments as indicated on top. Top panel, fluorogram of methylated H3. Bottom two panels, Coomassie stained gels for H3 substrate and the MLL1 core components used in the same reaction. (D) In vitro HMT assay using various RbBP5 peptides at equal molar concentration (5 µM) as indicated on top. Top panel, fluorogram of methylated H3. Bottom two panels, Coomassie stained gels for H3 substrate and the MLL1 core components used in the same reaction. Ash2L^SPRY and MLL1^SET were run at about the same position. RbBP5 peptides were run out of the gel due to their small sizes.