THE HEMATOPOIETIC GROWTH FACTOR-KL IS ENCODED BY THE SI-LOCUS AND IS THE LIGAND OF THE C-KIT RECEPTOR, THE GENE-PRODUCT OF THE W-LOCUS

Mutations at the steel locus (SI) of the mouse affect the same cellular targets as mutations at the white spotting locus (W), which is allelic with the c-kit proto-oncogene. We show that KL, a hematopoietic growth factor obtained from conditioned medium of BALB c 3T3 flbroblasts that stimulates the proliferation of mast cells and early erythroid progenitors, specifically binds to the c-kit receptor. The predicted amino acid sequence of isolated KL-specific cDNA clones suggests that KL is synthesized as an integral transmembrane protein. Linkage analysis maps the KL gene to the SI locus on mouse chromosome 10, and KL sequences are deleted in the genome of the SI mouse. These results indicate that the SI locus encodes the ligand of the c-kit receptor, KL. © 1990.