Hematopoietic receptors of class III receptor-type tyrosine kinases.

Receptor-type tyrosine kinases (RTKs) constitute a family of proteins involved in growth and developmental processes. Class III RTKs are characterized by an extracellular region composed of five immunoglobulin-like domains and by a split tyrosine kinase domain. Some of the class III RTKs perform major functions in hematopoiesis and are the focus of this review. They are the colony-stimulating factor-1 (CSF1) and Steel factor (SLF) receptors, encoded by the FMS and KIT protooncogenes, respectively, and the product of the FLT3/FLK2 gene. The structural, biochemical, functional, and pathological features of these three receptors and genes are reviewed.