Fred Sanger - Double Nobel Laureate: Radioactive sequencing of proteins and nucleic acids

The lean years Fred described 1955–64 as his ‘lean years’ as he published relatively little then. In fact, this was a transitional period in which Fred was exploring completely new ideas for sequencing proteins. His idea was to radioactively label proteins. After radioactively labelling a protein and then isolating a radioactive peptide, he would work out the sequence around the labelled amino acid, indirectly. For example, he would use various modifications of the peptide, e.g. removal of the N-terminal amino acid, and monitor changes in the mobility of the peptide on paper chromatography or paper electrophoresis. He was using the position of the peptide as a way of sequencing. This new way of thinking would, in principle, have many advantages. It would not require as much protein as his classical procedures worked out on insulin, since radioactively labelled peptides would be easily and quickly detected on paper by the then relatively new and sensitive method of autoradiography – using an X-ray film. The protein would not necessarily have to be pure, as long as it was radiochemically pure. For example in 1958 Fred incubated an isolated oviduct from a hen with 1 mCi 32 P-labelled inorganic phosphate. He successfully isolated 32 P-labelled ovalbumin, which was known then to contain two serine phosphates. Fred correctly deduced the presence of one phosphate-containing dipeptide, as serine phosphate-alanine, an observation confirmed ten years later by classical methods of peptide sequencing. Twenty years later on in 1978, in a very different era of DNA sequencing, my colleagues and I showed the exact position of this dipeptide in ovalbumin, as deduced from the nucleotide sequence of a cDNA clone of ovalbumin mRNA.