The molecular hug between the ER and the mitochondria

A long-observed but often neglected property of cellular organelles is their ability to associate into junctions. Aspects of cell physiology appear more and more to depend upon these contact sites, as their central molecular components are being identified. Contact sites between the endoplasmic reticulum (ER) and the mitochondria are emerging as a prime example of such contacts. The physiological role of these contact sites, first thought to be limited to the facilitation of lipid and calcium exchange between the two organelles, is found to extend to unexpected aspects of mitochondria and ER functions.