The pre-autophagosomal structure organized by concerted functions of APG genes is essential for autophagosome formation

Macroautophagy is a bulk degradation process induced by starvation in eukar yotic cells. In yeast, 15 Apg proteins coordinate the formation of autophag osomes. Several key reactions performed by these proteins have been describ ed, but a comprehensive understanding of the overall network is still lacki ng. Based on Apg protein localization, we have identified a novel structure that functions in autophagosome formation. This pre-autophagosomal structu re, containing at least five Apg proteins, i.e. Apg1p, Apg2p, Apg5p, Aut7p/ Apg8p and Apg16p, is localized in the vicinity of the vacuole. Analysis of apg mutants revealed that the formation of both a phosphatidylethanolamine- conjugated Aut7p and an Apg12p- Apg5p conjugate is essential for the locali zation of Aut7p to the pre-autophagosomal structure. Vps30p/Apg6p and Apg14 p, components of an autophagy- specific phosphatidylinositol 3-kinase compl ex, Apg9p and Apg16p are all required for the localization of Apg5p and Aut 7p to the structure. The Apg1p protein kinase complex functions in the late stage of autophagosome formation. Here, we present the classification of A pg proteins into three groups that reflect each step of autophagosome forma tion.