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DNA Test Methods - DNA Sanger SequencingTimelines: 1975
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DNA sequencing
Code reading techniques
Harvard University biochemists Allen Maxam and Walter Gilbert develop a new method of DNA sequencing. The Maxam-Gilbert procedure involves carefully fragmenting radioactively-labeled strands of DNA by a series of chemical treatments, each targeting a specific nucleotide base (A,T,G, or C). The original sequence is then inferred by identifying the specific chemical modifications that individual fragments have undergone by means of electrophoresis (the separation of molecules by size and charge in an electrical field) and autoradiography (the use of x-ray film to detect levels of radioactivity). The procedure gains popularity because, unlike earlier methods, it can incorporate purified samples of double-stranded DNA that do not require repeated processing.
Two years later, a team in Fred Sanger’s lab across the water in Cambridge, England develops an alternative (called ‘chain termination’) that proceeds according to a similar analytic logic. It fragments, reads, and reassembles sequences, but requires fewer toxic chemicals and radioactive isotopes, is simpler to prepare and perform, and easier to scale up. Both of these methods provide significant gains in sequencing speed, efficiency, and throughput. For the valuable tools they provide to molecular biologists, Gilbert and Sanger share the 1980 Nobel Prize in Chemistry, along with Paul Berg who is recognized for his work on recombinant DNA.