Ezh2 Polycomb YY1 K27 HDAC1 MyoD SRF VPA Eed Vav1 BMI EZH2 Mib low human Ki heterochromatin HSalpha HP1 HSbeta HSgamma Yin Zeste STAT5 interleukin Oct Pax5 histone HPH RING1 BMI1 HPC2 RING1A EED