Autophagy factor required for autophagosome formation. Target of the TOR kinase signaling pathway that regulates autophagy through the control of the phosphorylation status of ATG13 and ULK1, and the regulation of the ATG13-ULK1-RB1CC1 complex. Under starvation conditions, is localized to puncate structures primarily representing the isolation membrane that sequesters a portion of the cytoplasm resulting in the formation of an autophagosome. Phosphorylated under nutrient-rich conditions; dephosphorylated during starvation or following treatment with rapamycin. Belongs to the ATG13 family. Metazoan subfamily.