In the secretory pathway, proteins are transported from one organelle to another in vesicles that bud off from membranes. To prevent a misfolded protein or a resident protein of an organelle from being relocated, the ER retrieval pathway returns escaped proteins back to the ER. Generally, resident proteins are retained in the ER by chaperones such as BiP , while other proteins are recruited as cargo. When an incorrect protein binds the receptor and is transported out in a vesicle, it is returned via COPI vesicles that bud out from the vesicular tubular clusters or the Golgi apparatus. The retrieval pathway depends on short amino acid sequences called ER retrieval signals present at the C-terminus of ER proteins. The KKXX sequence, the best-characterized retrieval signal, consists of two lysines followed by two other amino acids and is recognized by receptors present in the vesicular tubular clusters. Another prominent sequence is the KDEL sequence, which contains lysine, aspartate, glutamate, and leucine residues. BiP contains a KDEL sequence that is recognized by the KDEL receptor. BiP secreted out from the ER is captured and loaded in a COPI vesicle, which transports it back to the ER. If the KDEL sequence is removed through genetic engineering, BiP is slowly secreted out of the ER without being returned.