Autophagy, the process of bulk degradation of cellular proteins through an autophagosomic-lysosomal pathway is important for normal growth control and may be defective in tumor cells. It is involved in the preservation of cellular nutrients under starvation conditions as well as the normal turnover of cytosolic components. This process is negatively regulated by TOR (Target of rapamycin) through phosphorylation of autophagy protein APG1. Another member of the autophagy protein family is ATG10, an E2-like enzyme involved in two ubiquitin-like modifications essential for autophagosome formation: ATG12-ATG5 conjugation and the modification of a soluble form of MAP-LC3, a homolog of yeast Apg8, to a membrane-bound form. ATG10 has also been shown to interact with ATG12 in human embryonic kidney cells in the presence of ATG7. Multiple isoforms of ATG10 are known to exist.