Cartoon of the ER-mitochondrial encounter structure (ERMES) in yeast, which facilitates calcium and phospholipid exchange, as well as possibly heme trafficking. ERMES consists of four proteins, Mdm12, Mmm1, Mdm34, and Mdm10, that physically tether the ER and outer mitochondrial membranes. Gem1 is a GTPase that disengages ERMES after mitochondrial fission. Altering the frequency of ERMES, by deletion of Gem1, or GTPases that control mitochondrial fusion, e.g. Mgm1, and fission, e.g. Dnm1, has been shown to affect mitochondrial-nuclear heme trafficking rates. See text for details.