Proto-oncogene tyrosine-protein kinase Fes/Fps, also known as Proto-oncogene c-Fes, Proto-oncogene c-Fps, Feline sarcoma oncogene, FES and FPS, is a protein which contains one FCH domain, one protein kinase domain and one SH2 domain. FES is a non-receptor protein tyrosine kinase expressed in hematopoietic progenitors and differentiated myeloid cells. FES is observed in the nuclear, granular and plasma membrane fractions of primary human neutrophils and the myeloid leukemia cell line, HL-60. The nuclear localization is confirmed by immunocytochemistry of neutrophils. FES has been implicated in granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) and erythropoietin signal transduction. FES has tyrosine-specific protein kinase activity and that activity is required for maintenance of cellular transformation. FES is also involved in normal hematopoiesis. Its chromosomal location has linked it to a specific translocation event identified in patients with acute promyelocytic leukemia.