Susumu Tonagawa made a major contribution to the understanding of the immune system by showing how gene fragments are rearranged in somatic cells to make functional immune system genes. For his work, he received the 1987 Nobel Prize in physiology or medicine.

Tonagawa was born in Nagoya, Japan, where his father was an engineer. Developing an interest in chemistry while in high school, Tonagawa took his undergraduate degree in that subject at the University of Kyoto in 1963. However, in his senior year he read papers on the operon theory by the French biochemists François Jacob and Jacques Monod, and subsequently switched to molecular biology for graduate studies, earning his Ph.D. in 1978 at the University of California, San Diego.

He began specializing in immunology while working at the Basel (Switzerland) Institute for Immunology, and in 1981 he joined the faculty of the Massachusetts Institute of Technology (MIT) Center...