Setting the standards: Quality control in the secretory pathway

A variety of quality control mechanisms operate in the endoplasmic reticulu m and in downstream compartments of the secretory pathway to ensure the fid elity and regulation of protein expression during cell Life and differentia tion. As a rule, only proteins that pass a stringent selection process are transported to their target organelles and compartments. If proper maturati on fails, the aberrant products are degraded. Quality control improves fold ing efficiency by retaining proteins in the special folding environment of the endoplasmic reticulum, and it prevents harmful effects that could be ca used by the deployment of incompletely folded or assembled proteins.