The endoplasmic reticulum serves many general functions,
including the facilitation of protein folding and the transport of
synthesized proteins in sacs called cisternae.
Correct folding of newly-made proteins is made possible by
several endoplasmic reticulum chaperone proteins, including protein
disulfide isomerase (PDI), ERp29, the Hsp70 family member Grp78,
calnexin, calreticulin, and the peptidylpropyl isomerase family.
Only properly-folded proteins are transported from the rough ER to
the Golgi complex.