Walter Gilbert (1932- present) was awarded a quarter of the 1980 Nobel Prize in Chemistry for his development of a method for determining the sequence of nucleotides in nucleic acids. Gilbert demonstrated the existence of a protein in the bacterium Escherichia coli that prevents a gene from manufacturing a certain enzyme, except in the presence of lactose. This confirmed Jacques Monod and Francois Jacob’s theory of the existence of “repressor proteins” that control genes responsible for beginning and ending protein synthesis in a cell. Later Gilbert created a widely-used technique using gel electrophoresis to examine the nucleotide sequence of DNA segments. Gilbert also first proposed the term “RNA world” hypothesis for the origin of life, which states that RNA appeared on Earth before and was a precursor to DNA and proteins.