BMI- 1 is one of polycomb group genes,which together with Ring1 strongly enhances the E3 ubiquitin ligase activity of the Ring2 catalytic subunit. Bmi1 plays an important role in the regulation of cell proliferation and senescence through repression of the p16Ink4a and p19Arf genes and is required for maintenance of adult hematopoietic and neural stem cells. The antibody reacts with the 37kd BMI1 protein.