Beadle and Tatum proposed the one gene-one enzyme hypothesis which suggested that the action of each gene is through the synthesis of a protein (enzyme), which in turn catalyses a single chemical reaction. Jacob and Monod provided genetic evidence for a method of gene regulation in bacteria now called the operon. Watson and Crick (1953) proposed the molecular structure of DNA. Laederberg (1946) first demonstrated the phenomenon of recombination in the bacteria.