You examine a cell line in which Ras is always activated even in the absence of a signaling molecule. This causes constant activation of the kinases in the MAP kinase pathway. Which of the following conditions would be MOST likely to turn off this abnormally active signaling pathway?
the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus
the addition of a drug that prevents the dimerization of the receptor kinase
the addition of a drug that increases the binding affinity of Ras for MAP kinase enzymes in the cytoplasm
the addition of a drug that prevents the phosphorylation of the receptor kinase