To isolate novel ETS genes expressed in hematopoietic cells we used a nested, degenerate oligonucleotide PCR based technique to obtain a cDNA fragment that encodes an ETS domain from a human megakaryocytic cell line. This fragment was used to isolate a full length, 4.2 kb cDNA that encodes a 663 amino acid protein which we call MEF (myeloid elf-1-like factor). MEF contains a central ETS domain and is expressed in a variety of myeloid leukemia cell lines and in normal adult hematopoietic tissue such as spleen, thymus and peripheral blood, as well as non-hematopoietic tissue such as ovary, placenta and colon. Using an oligonucleotide binding selection assay, and bacterially expressed MEF, we demonstrated that MEF recognizes a consensus DNA binding sequence nearly identical to elf-1 (..WGGA..) and then showed that MEF specifically bound to known elf-1 binding sites in the human GM-CSF and IL-3 promoters. To characterize the functional effect of MEF on transcription, we performed co-transfection experiments in myeloid cells, and T cells, and demonstrated transactivation of both promoters by MEF, but not by elf-1. MEF is a new member of the elf-1/E74 family of ETS proteins, that has DNA binding properties similar to elf-1 but distinct transcriptional activating effects in several hematopoietic cell lineages.