PBX1, also named as Pre-B-cell leukemia transcription factor 1, which belongs to the TALE/PBX homeobox family.PBX1 acts as atranscriptional activator of PF4 in complex with MEIS1. Isoform PBX1b as part of a PDX1:PBX1b:MEIS2b complex in pancreatic acinar cellsis involved in the transcriptional activation of the ELA1 enhancer.