Acts as a transcriptional regulator of PAX6. Acts as a transcriptional activator of PF4 in complex with PBX1 or PBX2. Required for hematopoiesis, megakaryocyte lineage development and vascular patterning. May function as a cofactor for HOXA7 and HOXA9 in the induction of myeloid leukemias. Defects in MEIS1 could be a cause of susceptibility to restless legs syndrome type 7 (RLS7). Restless legs syndrome (RLS) is a neurologic sleep/wake disorder characterized by uncomfortable and unpleasant sensations in the legs that appear at rest, usually at night, inducing an irresistible desire to move the legs. The disorder results in nocturnal insomnia and chronic sleep deprivation. Belongs to the TALE/MEIS homeobox family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.