Process of autophagy. Autophagy includes five phases: initiation, elongation and autophagosome formation, fusion, and autolysosome formation. Macromolecules are targeted to double-membrane vesicles called autophagosomes and then autolysosomes form by fusion with lysosomes. Autophagy is initiated by the ULK1 complex containing ULK, Atg13, FIP200, and Atg101. Autophagosome elongation and maturation involves two ubiquitin-like conjugation systems, such as the microtubule-associated protein 1 light chain 3 (LC3) and the Atg12 systems. The autophagosome fuses with a lysosome to form an autolysosome, which degrades macromolecules into amino acids, fatty acids, and nucleotides.