Sato, M.S. Brown, X.X. Hua, J.L. Goldstein, "Srebp-1, a membrane-bound transcription factor released by sterol-regulated proteolysis," Cell ... Goldstein, chairman and professor of molecular genetics ...

they used cryo-electron microscopy to visualize the structure of the protein at high and low pH. The structures reveal a tunnel that passes through the protein, with a sterol molecule located inside.