Chapter 16, Problem 12Q

Summary Introduction

To explain: The abnormalities expected by a GTPase-activating protein mutant cell in which Ras activity responds to extracellular signals.

Concept introduction: Ras is the first oncogene to have been identified. Ras is an intermediate protein in the MAP kinase pathway to activate the early G1 phase genes of the cell cycle. Ras is inactive when it is GDP bound. SOS, a Guanine nucleotide Exchange Factor (GEF) activates the Ras by changing its GDP to GTP. The cascade goes on till MAP kinase is activated. Then, a GTPase-activating protein (GAP) induces Ras. Ras hydrolyses the GTP bound to it to GDP thus inactivating it. Thus, one protein activates it and another protein inactivates it.