Stimulated B lymphocytes switch from the synthesis of membrane-bound to secreted antibody molecules by increasing the concentration of a subunit of the trimeric CstF complex that cleaves and polyadenylates mRNAs. How does this up-regulation of CstF bring about the production of soluble antibodies?
A) It favors a strong polyadenylation site in the immunoglobulin primary transcript, creating a longer antibody molecule that is secreted.
B) It activates a weak polyadenylation site in the immunoglobulin primary transcript and prevents splicing, creating a shorter molecule that is secreted.
C) It favors a strong polyadenylation site in the immunoglobulin primary transcript, creating a shorter antibody molecule that is secreted.
D) It activates a weak polyadenylation site in the immunoglobulin primary transcript, creating a longer antibody molecule that is secreted.
E) It favors a strong polyadenylation site in the immunoglobulin primary transcript, aborting translation and creating a shorter antibody molecule that is secreted.

Question

Quizplus · Accepted Answer

The suboptimal cleavage/poly-A addition site in the transcript is encountered first but is usually skipped in unstimulated B lymphocytes, leading to production of a longer antibody molecule that is anchored in the plasma membrane. When activated to produce antibodies, the B lymphocyte increases its CstF concentration; as a result, cleavage now occurs at the suboptimal site, and the shorter transcript is produced.

Stimulated B Lymphocytes Switch from the Synthesis of Membrane-Bound to Secreted