Apg10p, a novel protein-conjugating enzyme essential for autophagy in yeast

Autophagy is a cellular process for bulk degradation of cytoplasmic compone nts. The attachment of Apg12p, a modifier with no significant similarity to ubiquitin, to Apg5p is crucial for autophagy in yeast, This reaction proce eds in a ubiquitination-like manner, and requires Apg7p and Apg10p, Apg7p e xhibits a considerable similarity to ubiquitin-activating enzyme (E1) and i s found to activate Apg12p with ATP hydrolysis. Apg10p, on the other hand, shows no significant similarity to other proteins whose functions are known . Here, we show that after activation by Apg7p, Apg12p is transferred to th e Cys-133 residue of Apg10p to form an Apg12p-Apg10p thioester, Cells expre ssing Apg10p(C133S) do not generate the Apg12p-Apg5p conjugate, which leads to defects in autophagy and cytoplasm-to-vacuole targeting of aminopeptida se I. These findings indicate that Apg10p is a new type of protein-conjugat ing enzyme that functions in the Apg12p-Apg5D conjugation pathway.