Jianhua Zhao, PhD, is an assistant professor in the Cancer Metabolism and Microenvironment Program at Sanford Burnham Prebys.

The first figure in the paper discusses several stages in the formation of the 20S proteasome, which is shaped like a barrel. This proteasome is marked by the coming together of four stacked rings comprised each of seven protein building blocks known as either alpha or beta subunits. The two rings of beta subunits at the center are sandwiched by two rings of alpha subunits.