Clathrin-coated vesicles bud from eukaryotic plasma membrane fragments when adaptins, clathrin, and dynamin-GTP are added.

A. adaptins were omitted

B. Clathrin was omitted

C. Dynamin was omitted

D. Prokaryotic membrane fragments were used

Viruses are the ultimate scavenger-a necessary consequence of their small genomes. Wherever possible they make use of the cell's machinery to accomplish the steps involved in their own reproductions. Many different viruses have membrane coverings. These so-called enveloped viruses gain access to the cytosol by fusing with a cell membrane. Why do you suppose that each of these viruses encodes its own special fusion protein, rather than making use of a cell's SNAREs?