Molecular Biology Of The Cell 6th Edition by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter

Exercise 5

1 If the enzyme dihydrofolate reductase (DHFR), which is normally located in the cytosol, is engineered to carry a mitochondrial targeting sequence at its N-terminus, it is efficiently imported into mitochondri a. If the modified DHFR is first incubated with methotrexate, which binds tightly to the active site, the enzyme remains in the cyto- sol. How do you suppose that the binding of methotrexate interferes with mitochondrial import?