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 Jacobâ€™s theory of the existence of â€œrepressor proteinsâ€ 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 â€œRNA worldâ€ hypothesis for the origin of life, which states that RNA appeared on Earth before and was a precursor to DNA and proteins.