Conserved regulation of autophagosome-lysosome fusion through YKT6 phosphorylation.

YKT6 is a SNARE (Soluble N-ethylmaleimide-Sensitive Fusion Protein Attachment Protein Receptor) protein governing membrane fusion events of several cellular organelles. In autophagy, YKT6 is involved in early phagophore formation as well as directly in the fusion process between autophagosomes and the lytic compartment. Recently we showed in yeast, mammalian cells, and nematodes that the function of YKT6 in autophagy can be regulated by phosphorylation. Atg1/ULK1 (Unc-51-like kinase 1)-dependent phosphorylation of YKT6 results in autophagy defects during both early (autophagosome formation) and late (autophagosome-lysosome fusion) steps, ultimately resulting in decreased survival of mammalian cells due to defective stress-induced autophagy. These findings show that not only the function but also the regulation of YKT6 is conserved across species.