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 Solution Answer: B. II and III The ActA (Actin assembly-inducing protein) is an integral membrane protein expressed on the cell surface of bacterium Listeria and causes the polymerization of protein released by actin filaments (of host mamalian cell) at the end of the bacterium. Thus, ActA is the only bacterial protein that is required for the movement of the bacterium within its host cell. All the five observations given in the questions are true in reference to ActA protein which is associted to the bacterial intracellular movement. However, if we have to select the combination from the 5 observations which are showing that ActA is both, necessary and sufficient for bacterial movement, the combination of the observations II and III is true. 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..

1. 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
Solution
Answer: B. II and III
The ActA (Actin assembly-inducing protein) is an integral membrane protein expressed on the
cell surface of bacterium Listeria and causes the polymerization of protein released by actin
filaments (of host mamalian cell) at the end of the bacterium. Thus, ActA is the only bacterial
protein that is required for the movement of the bacterium within its host cell.
All the five observations given in the questions are true in reference to ActA protein which is
associted to the bacterial intracellular movement. However, if we have to select the combination
from the 5 observations which are showing that ActA is both, necessary and sufficient for
bacterial movement, the combination of the observations II and III is true.
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.