The pleiotropic role of autophagy: from protein metabolism to bactericide.

Autophagy is in principle a nonselective, bulk degradation system within cells, with a contribution to intracellular protein degradation estimated to be as large as that of the ubiquitin--proteasome system. The primary roles of autophagy are baseline turnover of intracellular proteins and organelles, production of amino acids in nutrient emergency, and regression of retired tissues. These functions guarantee rejuvenation and adaptation to adverse conditions, and even underlie dynamic processes such as development/metamorphosis. In addition, several other roles for autophagy have recently been discovered, such as presentation of endogenous antigens and degradation of invasive bacteria. This review will discuss the biological significance of autophagy from yeast to higher eukaryotes.