Atg and Atg-related Protein  (Atg和Atg相关蛋白)

The Atg proteins involved in autophagosome formation consist of several functional units: Atg1 kinase and its regulators, the PI3K complex, Atg9, the Atg2-Atg18 complex, and two ubiquitin-like conjugation systems. Although most Atg proteins seem to be involved mainly in autophagy, some of them have been shown to exhibit nonautophagic functions.

Atg1/Unc-51-like kinase (ULK) is the only protein kinase among the Atg-related proteins. The major subunits of the yeast Atg1 complex include Atg1, Atg11, Atg13, Atg17, Atg29, and Atg31. Although Atg11 is not essential for canonical autophagy, it is required for the cytoplasm-to-vacuole targeting (Cvt) pathway (an autophagy-related constitutive transport system in yeast that delivers some vacuolar enzymes) and forms a scaffold with Atg17. Atg17, Atg29, and Atg31 form a stable protein complex irrespective of nutrient conditions, and Atg1 and Atg13 are incorporated into the Atg17-Atg29-Atg31 complex under autophagy-inducible conditions. The association of Atg13 and Atg17 is important for Atg1 kinase activation during starvation. A systematic hierarchical analysis performed in yeast revealed that the Atg1 complex is the farthest upstream unit.