Atg41/Icy2 regulates autophagosome formation.

Macroautophagy (hereafter autophagy) is one of the major degradation systems in eukaryotic cells, and its dysfunction may result in diseases ranging from neurodegeneration to cancer. Although most of the autophagy-related (Atg) proteins that function in this pathway were first identified in yeast, many were subsequently shown to have homologs in higher eukaryotes including humans, and the overall mechanism of autophagy is highly conserved. The most prominent feature of autophagy is the formation of a double-membrane sequestering compartment, the phagophore; this transient organelle surrounds part of the cytoplasm and matures into an autophagosome, which subsequently fuses with the vacuole or lysosome to allow degradation of the cargo. Much attention has focused on the process involved in phagophore nucleation and expansion, but many questions remain. Here, we identified the yeast protein Icy2, which we now name Atg41, as playing a role in autophagosome formation. Atg41 interacts with the transmembrane protein Atg9, a key component involved in autophagosome biogenesis, and both proteins display a similar localization profile. Under autophagy-inducing conditions the expression level of Atg41 increases dramatically and is regulated by the transcription factor Gcn4. This work provides further insight into the mechanism of Atg9 function and the dynamics of sequestering membrane formation during autophagy.