Conserved ubiquitin-like modifier involved in autophagy and the Cvt pathway; conjugated to Atg5p forming a complex involved in Atg8p lipidation; Atg5p-Atg12p conjugate enhances E2 activity of Atg3p by catalytic site rearrangement; also forms a complex with Atg16p; the Atg5-Atg12/Atg16 complex binds to membranes and is essential for autophagosome formation; disordered N-terminus protects the C-terminus and is a negative regulator of Atg7–Atg12 conjugation and autophagy; homolog of mammalian ULK1