Structure of the 26S proteasome. The 20S core of the proteasome is shown in grey. One copy of each of the β1, β2, and β5 active sites is present within each of two seven-subunit rings (the positions of which are marked with dashed blue lines) and face towards the inside of the 20S chamber. Each end of the 20S core is capped with a 19S regulatory particle, shown in various colors. The Rpt1-6 ATPase ring that abuts the 20S core is shown in blue and Rpn11 in green. Rpn10 (purple) and Rpn13 (gold) are two intrinsic ubiquitin chain-binding receptors within the 26S proteasome. The pore in the ATPase ring through which the substrate passes is indicated. Electron density within the image that corresponds to substrate is shown in red. Adapted from .