Question

Which of the following mutations could account for a cell line that is dividing more rapidly than expected?

	A.	A Ras-GAP mutation that causes enhanced activity
	B.	A Ras-GEF mutation that abolishes an SH2 domain used for RTK interaction
	C.	A Ras-GEF mutation that results in only 10% wild-type activity
	D.	A Ras-GAP mutation that results in only 10% wild-type activity
	E.	A Ras mutation that interferes with MAPKKK interaction

Answer 1

Ras protein, when bound to GTP, is an activator of cell division. Ras, when associated with GTPase Activating Protein (GAP), results in hydrolysis of GTP to GDP and Pi. So, Ras-GAP association results in inactive Ras protein and inhibits cell division. If the Ras-GAP activity is only 10% of WT, more Ras-GTP (active form) will be present and the cell will undergo quick cell division. So the correct option is D, a Ras-GAP mutation resulting in only 10% activity of the WT.