Gilbert, Walter (1932- )

US molecular biologist who studied genetic control, seeking the mechanisms that switch genes on and off. By 1966 he had established the existence of the lac repressor, a molecule that suppresses lactose production. Further work on the sequencing of DNA nucleotides won him a share of the 1980 Nobel Prize for Chemistry, with Frederick Sanger and Paul Berg. Gilbert was born in Boston, Massachusetts, and educated as a physicist at Harvard and at Cambridge, England. In 1960 he changed to biology, becoming professor of biophysics at Harvard 1964, then professor of molecular biology 1969. Gilbert began in 1965 his attempt to identify repressor substances involved in the regulation of gene activity. He devised a technique called equilibrium dialysis that enabled him to produce relatively large quantities of the repressor substance, which he then isolated and purified, and by late 1966 he had identified it as a large protein molecule. Gilbert then developed a method of determining the sequence of bases in DNA, which involved using an enzyme that breaks the DNA molecule at specific, known points.