Shapely ER and mitochondria pair up

The endoplasmic reticulum (ER) is a dynamic network of sheets and tubules that extends throughout the cytoplasm, and that makes close contacts with other organelles. Proteins that maintain the complex structure of the ER include the reticulons Rtn1p and Rtn2p, and the reticulon-like protein Yop1p in Saccharomyces cerevisiae, as well as the atlastin family of proteins – dynamin-like GTPases in mammalian cells and their functional homologue in yeast Sey1p. Surprisingly, yeast cells that lack ER-shaping proteins grow as well as wild-type cells, even though they contain fewer ER tubules. To gain insights into the role of ER morphology in cell physiology, William Prinz and co-workers screen for mutations that cause poor growth in yeast cells that lack ER-shaping proteins (p. 4791). They authors report that cells that lack members of the ER–mitochondria encounter structure (ERMES) complex – which maintains functional contacts between the ER and mitochondria – as well as ER-shaping proteins have severe growth defects, reduced ER to mitochondrial phospholipid transfer and an altered mitochondrial phospholipid content. Together, these results reveal an unexpected role for ER-shaping proteins in maintaining functional contacts between the ER and mitochondria, and suggest that the shape of the ER at ER–mitochondria contact sites affects lipid exchange between these organelles.