L3MBTL1 is a member of the polycomb group (PcG) proteins, which function as transcriptional regulators in large protein complexes. In Drosophila, homozygous mutations in the L3MBTL1 gene have been demonstrated to cause brain tumors, identifying L3MBTL1 as a tumor suppressor gene. L3MBTL1 forms a homodimer and interacts with TEL (ETV6). L3MBTL1 probably plays a role in cell proliferation. Overexpression of L3MBTL1 induces multinucleated cells, suggesting that it is required for normal mitosis.