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 Atg1. The Atg1-Atg13 complex functions at multiple levels to mediate and adjust nutrient-dependent autophagic signaling. Involved in the autophagic degradation of dBruce which controls DNA fragmentation in nurse cells. Interacts with Atg1. 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 in a nutrient-, TOR- and Atg1 kinase-dependent manner. Results in late stage egg chambers that contain persisting nurse cell nuclei without fragmented DNA and attenuation of caspase-3 cleavage. Belongs to the ATG13 family. Metazoan subfamily.