Walter Gilbert and Allan Maxam developed a DNA sequencing method which combined chemicals that cut DNA only at specific bases with radioactive labeling and Southern blotting to determine the sequence of long DNA segments[3].
References
Gilbert, Walter and Maxam. Allan, The Nuclcotide Sequence of the Lac Operator, Proc. Natl. Acad. Sci. USA 70, 3581-3584 (1973).
Maxam AM, Tizard R, Skryabin KG, Gilbert W, Promotor region for yeast 5S ribosomal RNA, Nature. 1977 Jun 16;267(5612):643-5