Myeloid Elf-1 like factor (MEF) is an ETS protein, which activates the promoters of granulocyte macrophage colony-stimulating factor, interleukin-3, lysozyme, human beta defensin-2 and perforin. In spite of its many known functions, little is known about MEF transcriptional regulation. Here, we cloned the 5'-flanking region of human MEF gene and identified a TATA-less promoter region at -204/-54 which contains 4 putative binding sites for Sp1, two of which are essential in up-regulating MEF activity. These were proven by EMSA and blocking Sp1 using RNAi or mithramycin A treatment of HEK293 cells. Our results suggest that Sp1 constitutively regulates the MEF gene.