Autophagosome elongation Atg5 and Atg12 are involved in the first of two ubiquitylation-like reactions that control autophagy. Atg12 is conjugated to Atg5 in a reaction that requires Atg7 [ubiquitin-activating-enzyme (E1)-like] and Atg10 [ubiquitin-conjugating-enzyme (E2)-like]. Atg5-Atg12 conjugates are localised onto the PAS and dissociate upon completion of autophagosome formation. The process of Atg5-Atg12 conjugation depends on Vps34 function, and Vps34 activity, along with autophagy, is positively regulated by the small GTPase Rab5 (Ravikumar et al., 2008). Atg5-Atg12 interacts non-covalently with Atg16L (Atg16-like) to form a complex of approximately 800 kDa (Ohsumi and Mizushima, 2004).

The second ubiquitylation-like reaction involves the conjugation of microtubuleassociated protein 1 light chain 3 (MAP1-LC3; also known as Atg8 and LC3) to the lipid phosphatidylethanolamine (PE). LC3 is cleaved at its C-terminus by Atg4 to form cytosolic LC3-I, which is covalently