Bmi1 is a ring finger protein that is major component of the polycomb group complex 1 (PRC1). Bmi1 protein plays a crucial role in cellular processes, particularly in gene expression regulation and stem cell properties maintenance. Bmi1 is primarily located in the nucleus, where Bmi1 functions as a transcriptional repressor, interacting with chromatin and influencing expression of genes involved in cell cycle regulation and development. Nuclear localization allows Bmi1 to modulate transcription of target genes, including those associated with oncogenesis and stem cell maintenance. Bmi1 has been implicated in repression of the Ink4a/Arf locus, which is essential for controlling cellular senescence and tumor suppression.