FES proto-oncogene, FES, is the human cellular counterpart of a feline sarcoma retrovirus protein with transforming capabilities. FES has tyrosine-specific protein kinase activity and that activity is required for maintenance of cellular transformation. Its chromosomal location has linked it to a specific translocation event identified in patients with acute promyelocytic leukemia but it is also involved in normal hematopoiesis as well as growth factor and cytokine receptor signaling.