- A point mutation at tyrosine-809 in the human colony-stimulating factor 1 receptor impairs mitogenesis without abrogating tyrosine kinase activity, association with phosphatidylinositol 3-kinase, or induction of c-fos and junB genes. Roussel, M.F., Shurtleff, S.A., Downing, J.R., Sherr, C.J. Proc. Natl. Acad. Sci. U.S.A. (1990)