The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration to RGF would be most likely to prevent receptor dimerization?
(a) a mutation that increases the affinity of RGFR for RGF
(b) a mutation that prevents RGFR from binding to RGF
(c) changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines
(d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid