You are studying a protein in Salmonella typhimurium that you believe is a toxin. Whenever you attempt to purify the protein from lysed cell cultures, you get two forms of the protein. One form is smaller than the other and is missing 15 amino acids from the N-terminus compared to the larger form. This leads you to hypothesize that
A) there are two termination sites in the mRNA.
B) the protein requires chaperonins to fold properly.
C) the protein is secreted and folds outside of the cell.
D) you need to re-do the experiment because there should only be one form.

Question

Quizplus · Accepted Answer

The presence of two forms of the protein suggests that the protein is being cleaved or processed after it is synthesized, and that the smaller form is missing 15 amino acids from the N-terminus. This is consistent with the idea that the protein is being secreted and cleaved externally to the cell.

You Are Studying a Protein in Salmonella Typhimurium That You