Walter Gilbert

Walter Gilbert, born in 1932, American molecular biologist and Nobel Prize winner. Gilbert's work involved the nucleic acid deoxyribonucleic acid (DNA), the genetic material of cells. He made it possible to determine the exact sequence of bases (molecular compounds in DNA that form genes) in only one day. Before Gilbert's technique, sequencing a gene took years. For making it possible to study the chemical structure of genes in greater detail, Gilbert was awarded the 1980 Nobel Prize in chemistry. He shared the prize with British biochemist Frederick Sanger and fellow American molecular biologist Paul Berg, a pioneer in genetic engineering.

Born in Boston, Massachusetts, Gilbert received his M.S. degree from Harvard University and his Ph.D. degree from the University of Cambridge in England. He then returned to Harvard and was appointed assistant professor of physics in 1959. Starting in 1960 Gilbert grew increasingly interested in biochemistry and molecular biology and became professor of biochemistry in 1968. From 1972 to 1982 he served as chair for molecular biology at Harvard. From 1982 to 1984 Gilbert served as chairman of the Swiss gene-splicing firm Biogen, which he helped found in 1978. After returning to Harvard, he helped launch the United States Human Genome Project, designed to sequence all 3 billion bases in human DNA. In 1987 he started the Genome Corporation to sequence human DNA and market the information.

Gilbert did not originally set out to discover a sequencing method. The idea came to him during unrelated research that involved breaking strands of DNA at particular points. A DNA strand is made up of structural units called nucleotides. Each nucleotide contains one of four bases: adenine (A), cytosine (C), guanine (G), and thymine (T). Cytosine can only link with guanine, and adenine can only link with thymine. Gilbert knew that dimethyl sulfate, an industrial poison, breaks DNA strands at A or G sites, and that hydrazine, a gaseous compound, weakens C and T sites. After experimenting with different combinations, he developed four chemicals that broke DNA consistently at the sites of all four bases. By passing each DNA fragment through a thin gel, he was able to capture their images on photographic paper. This created a complete map of the order of bases on the original DNA strand. At the same time Gilbert was perfecting his method, British biochemist Frederick Sanger developed a different sequencing technique. Both became widely used.