Self-eating ERs

When under stress, the ER of yeast cells expands greatly in size but also eats its own membrane stacks to form autophagosome-like structures, say Sebastián Bernales, Kent McDonald, and Peter Walter (University of California, San Francisco, CA). The process may cleanse the ER of unfolded proteins that would otherwise clog the secretory pathway.

An overworked ER sends out a distress signal called the unfolded protein response (UPR). The UPR helps the ER cope by increasing its folding capacity, and jettisoning those proteins that are hopelessly misfolded. The authors found that, under UPR-inducing conditions, most stressed cells had ER networks that are fivefold bigger than normal. But their electron micrographs also revealed many cells containing normal-sized ERs along with autophagosome-like structures packed selectively with ER stacks. The outer membranes of these structures were also...