Question

Results from multiple experiments suggest that the ActA protein of Listeria, an integral membrane protein expressed on the cell surface, is the only bacterial protein that is required for the movement of the bacterium within its host cell. Which combination of the following observations shows that ActA is both, necessary and sufficient for bacterial movement?
Please note: E. Coli is not an intracellular bacterium - it does not normally move inside the cytosol, and it does not express ActA.

I. ActA binds to the Arp2/3 complex

II. E. Coli in which ActA is expressed moves in host cell cytosol

III. Listeria lacking the ActA gene fail to move inside the host cell cytosol.

IV. ActA has 3 transmembrane domains

V. Arp2/3, when activated, nucleates a branched actin network

A. I and II

B. II and III

C. I and III

D. III and IV

E. I and V

Answer 1

Answer:

The correct answer is option B. "II and III".

Explanation:

In order to prove that ActA protein of Listeria is necessary and sufficient for bacterial movement within its host cell a series of results in transformed Listeria and transformed E. Coli must be obtained. First, if Listeria lacking the ActA gene fail to move inside the host cell cytosol it will prove that ActA is necessary for bacterial movement. Second, a transformed E. Coli that expresses ActA should be able to move in host cell cytosol. Wild type E. Coli does not expresses ActA, if ActA alone makes E. Coli able to move in host cell cytosol it will prove that ActA is sufficient for bacterial movement.