Atg14 is a key factor in determining the function of the PtdIns 3-kinase complex. (a) Membrane dynamics of autophagy and movement of PtdIns(3)P in yeast. The isolation membrane extends to enclose the cytoplasmic contents. The closed double-membrane structure, the autophagosome, fuses with the vacuole and releases the inner membrane structure, the autophagic body, into the lumen where the enclosed contents are degraded [25]. PtdIns(3)P (bold line) is enriched at the inner surface of the isolation membrane and the autophagosome [26]. PtdIns(3)P is also enriched on some uncharacterized amorphous membranes near the tips of the isolation membrane. (*) In mammals the autophagosome fuses with the lysosome, which is often smaller than the autophagosome, and the released lysosomal hydrolytic enzymes degrade the inner membrane structure to become the autolysosome. (b) Assortment of PtdIns 3-kinase complexes in yeast. Yeast has at least two PtdIns 3-kinase complexes (Complexes I and II). Atg14 is a specific subunit of Complex I. Atg14 targets Complex I to the PAS, thereby, providing Complex I with the ability to function in autophagy. In mammals, in addition to Complexes I and II, a third complex exists in which Rubicon is added to Complex II; this complex negatively regulates maturation of the autophagosome. (*) Instead of the PAS, Barkor/Atg14(L) targets the autophagy-specific PtdIns 3-kinase complex to an ER subdomain in mammalian cells. (**) Although endosomal localization of the complete Complex II (including Atg6) is dependent on Vps38, that of Vps34 and Vps15 does not require Vps38. (a) and (b) reproduced from Obara and Ohsumi [26] (Copyright 2008 by Landes Bioscience) and [17] (Copyright 2011 by the Hindawi Publishing Corporation), respectively.
