The structure (left) and a simplified model (right) of the yeast 26S proteasome. The structure of 26S proteasome was reprinted from Proceedings of the National Academy of Sciences, USA 92. The proteolytic active subunits (β1, β2 and β5) are highlighted in red color. Rpt, regulatory particle triple-A ATPase, Rpn, regulatory particle non-ATPase.