Transcription repression by β/SMMHC. U937 cells were transfected with M-CSF-R-luc plasmid (1 μg) with mutated RUNX binding site (lanes 2-4) or wild-type site (lanes 5-28), together with expression plasmids for RUNX1 (0.5 μg, a full dose) and PEBP2β1 (0.25 μg, a half dose) as indicated. On top of it, a half dose of PEBP2β isoforms or β/SMMHC mutant expression vectors were transfected in such a way as to mimic the conditions of inv(16) cells. A total of 2 μg DNA including 1 ng Renilla luciferase expression plasmid as an internal control was used. Luciferase activities are expressed as fold changes relative to the control transfected with M-CSF-R-luc and the backbone expression vector. The data are mean of 3 independent experiments and the values were normalized using luciferase activities. Standard deviations are indicated by error bars. Horizontal line indicates the level of transactivation attained by a full dose of RUNX1 and a half dose of PEBP2β1. Above this line is considered to be transcription stimulation by each construct and below the line, repression.