<prompt> Synthesis of an immunoglobulin in membrane-bound or secretory form is determined byOne turn to two turn joining ruleClass switchingDifferential RNA processingAllelic exclusion  <response>: The regulation of gene expression is not confined to the differential transcription of DNA. Even if a paicular RNA transcript is synthesized, there is no guarantee that it will create a functional protein in the cell. To become an active protein, the RNA must be 1 processed into a messenger RNA by the removal of introns, 2 translocated from the nucleus to the cytoplasm, and 3 translated by the protein-synthesizing apparatus. In some cases, the synthesized protein is not in its mature form and 4 must be posttranslationally modified to become active. Regulation can occur at any of these steps during development. 