© G.E. KIDDLER SMITH/CORBIS
In the mid-1980s, biochemist Leonard Rome of the University of California, Los Angeles, (UCLA) School of Medicine and his postdoc Nancy Kedersha were developing new ways to separate coated vesicles of different size and charge purified from rat liver cell lysates when they stumbled upon something else entirely. They trained a transmission electron microscope on the lysate to check whether the vesicles were being divvied up correctly, and the resulting image revealed three dark structures: a large protein-coated vesicle, a small protein-coated vesicle, and an even smaller and seemingly less dense object. (See photograph below.) The researchers had no idea what the smallest one was.
“There were many different proteins and membrane-bound vesicles in the various fractions we analyzed,” Kedersha recalls, but this small vesicle ...
