Autophagy-specific protein that functions in response to autophagy-inducing signals as a scaffold to recruit other ATG proteins to organize preautophagosomal structure (PAS) formation. Modulates the timing and magnitude of the autophagy response, such as the size of the sequestering vesicles. Plays particularly a role in pexophagy and nucleophagy (By similarity). Impairs atg8-processing. Belongs to the ATG17 family.