Working model. Small selective autophagosomes are formed under nutrient-rich conditions. For formation of larger bulk autophagosomes, the upregulation of Atg1 kinase activity, bulk-specific components and/or the increase of such components is required. Once an autophagosome is sealed, fusion promoting factors such as SNARE proteins need to associate with the autophagosome and fusion-inhibitory factors need to be removed, potentially also regulated by Atg1 kinase activity. Together, these events regulate the faithful formation of the right autophagosomes at the right time, and prevent their premature fusion with the lytic compartment.