In 1977 American physicist, biochemist and molecular biologist Walter Gilbert and his student Allan M. Maxam devised a new technique for sequencing DNA. In 1980 Gilbert shared the 1980 Nobel Prize in Chemistry with Frederick Sanger and Paul Berg. Paul Berg received half of the price "for his fundamental studies of the biochemistry of nucleic acids, with particular regard to recombinant-DNA". The other half was split between Walter Gilbert and Frederick Sanger "for their contributions concerning the determination of base sequences in nucleic acids".
“The Gilbert-Maxam method involved multiplying, dividing, and carefully fragmenting DNA. A stretch of DNA would be multiplied a millionfold in bacteria. Each strand was radioactively labeled at one end. Nested into four groups, chemical reagents were applied to selectively cleave the DNA strand along its bases--adenine (A), guanine (G), cytosine (C) and thymine (T). Carefully dosed, the reagents would break the DNA into a large number of smaller fragments of varying length. In gel electrophoresis, as a function of DNA’s negative charge, the strands would separate according to length, revealing, via the terminal points of breakage, the position of each base” (http://www.genomenewsnetwork.org/resources/timeline/1977_Gilbert.php, accessed 11-20-2013).
Maxam, A M; Gilbert, W. "A new method for sequencing DNA", Proc. Natl. Acad. Sci. U.S.A. (1977 Feb) 74 (2) 560–4.