PML I stimulates cooperation of AML1 and p300. (A) PML I specifically enhanced AML1-induced transcription. The effect of PML proteins on AML1-dependent transcription was investigated using the reporter gene under the control of mCCP1 promoter. PmL^-/- MEF cells were spread in 24-well plates and transfected with 50 ng of reporter gene, 200 ng of pLNCX-AML1b, 30 ng of empty vector or PML isoforms as indicated, and 2 ng of pRL-CMV. (B) PML I stimulates the cooperated transcription activity of AML 1 and p300. PmL^-/- MEF cells were spread in 24-well plates and transfected with 50 ng of CCP1-luc, 200 ng of pLNCX-AML1b (lanes 4-9), 250 ng of pCMV-p300 (lanes 6-9), and either 30 ng (lanes 2, 5, 8) or 100 ng (lanes 3, 6, 9) of pLNCX-PML I and 2 ng of pRL-CMV. Luciferase activity was assayed as described in the Experimental Procedure. (C) PML I recruits AML1b and p300 into nuclear bodies. SaOS2 cells were cotransfected with pCMV-p300 (i-iii) together with LNCX-FLAG-AML1b (ii, iii) and LNCX-HA-PMLI (i, iii). p300 stained with anti-p300 rabbit polyclonal antibody (N15) is shown by the green color, and PML (i) stained with anti-HA antibody (3F10) and AML1 (ii, iii) stained with anti-FLAG antibody (M2) are shown by orange color. Merging of the 2 colors results in a yellow signal, indicating the colocalization of 2 proteins. Nuclear staining with DAPI is shown by the blue color.