Adding highly antigenic peptides, called epitope tags, to the amino or carboxy terminus of a protein enhances the ability of commercially available antibodies to be used for Western blotting and immunoprecipitation. Which of the following best describes how epitope-tagged proteins are produced?

A. A unique peptide sequence, like the FLAG epitope, is chemically crosslinked to the mature protein of interest.
B. The gene encoding the protein of interest is modified to include a short sequence of amino acids that is not commonly found in proteins.
C. An epitope tag consisting of a long stretch of nonpolar amino acids is incorporated into the protein of interest.
D. A sequence of amino acids common to most proteins in the cell is added to the gene for the protein of interest.