Fig. 6
Pioneer factor model. We propose a model for the pioneer factor function of c-Myb (left panel) where c-Myb binds to closed chromatin, possibly marked by H3K4me1, then recruits H3K27 acetyltransferases such as p300/CBP, facilitating histone acetylation. Due to the reduced nucleosomal stability caused by histone acetylation, chromatin accessibility increases and c-Myb detaches from chromatin because of the lost interaction with acetylated histones. The pioneer-defect D152V mutant (right panel) binds to chromatin and recruits H3K27 acetyltransferases, but is unable to facilitate H3K27ac due to the weakened histone interaction. Therefore, the D152V mutant is unable to increase chromatin accessibility, and the chromatin-embedded target gene remains silent