Endoplasmic reticulum quality control is a vital process in all eukaryotic cells that ensures that only properly folded proteins leave the endoplasmic reticulum for transport to their final destination. Under normal cellular conditions, molecular chaperones and lectins recognize aberrant or unfolded proteins and target them for destruction in a procedure known as endoplasmic reticulum–associated degradation. However, when genetic mutations, translational errors, or cell stress lead to a toxic accumulation of unfolded proteins in the endoplasmic reticulum, this degradation process may be insufficient to prevent aggregation or blockage of the endoplasmic reticulum transport machinery, and a signal transduction pathway termed the unfolded protein response is activated. This pathway leads to increased synthesis of folding and degradative enzymes while decreasing overall new protein synthesis, which allows the endoplasmic reticulum to better handle the load of unfolded protein. If endoplasmic reticulum stress cannot be abated, apoptotic pathways can be initiated, ultimately leading to cell death.

Notably, much of the early research to discern the mechanisms of endoplasmic reticulum–associated degradation and the unfolded protein response was done in baker's yeast, Saccharomyces cerevisiae. All of the yeast components of these processes have homologs in mammals, although the mammalian systems are somewhat more complex.