Hierarchy of Atg proteins in pre-autophagosomal structure organization.

Autophagy is a bulk degradation process that is conserved in eukaryotic cells and functions in the turnover of cytoplasmic materials and organelles. When eukaryotic cells face nutrient starvation, the autophagosome, a double-membraned organelle, is generated from the pre-autophagosomal structure (PAS). In the yeast Saccharomyces cerevisiae, 16 ATG (autophagy-related) genes are essential for autophagosome formation. Most of the Atg proteins are involved in the PAS, leading to autophagosome production. However, the mechanism of PAS organization remains to be elucidated. Here, we performed a systematic and quantitative analysis by fluorescence microscopy to develop a hierarchy map of Atg proteins involved in PAS organization. This analysis suggests that Atg17p is the most basic protein in PAS organization: when it is specifically targeted to the plasma membrane, other Atg proteins are recruited to that location, suggesting that Atg17p acts as a scaffold protein to organize Atg proteins to the PAS.