Figure 1.

Htt may have evolved from Cvt proteins Atg23, Vac8 and Atg11. (A) The yeast Vac8 protein contains 11 armadillo repeats which can be described as ancestral HEAT repeats. Throughout evolution, Vac8 may have fused with yeast protein Atg23 on the amino-terminus and Atg11 on the C-terminus. These yeast proteins are essential for the cytoplasm to vacuole targeting (Cvt) selective autophagic pathway, which is activated by TORC1 in yeast grown under nutrient-rich conditions. The cartoon is not drawn to scale. (B) A protein complex essential for the yeast Cvt pathway may be similar to a hypothetical human complex required for selective macroautophagy under nutrient-rich conditions.