32P, 33P and 35S: selecting a label for nucleic acid analysis

Several criteria should determine which radioisotope is used to label nucleic acids; this labelling is a necessary step in many molecular biology research techniques including filter hybridization and DNA sequencing. Three radioisotopes are now available: phosphorus 32 (32P), sulphur 35 (35S) and the recently introduced phosphorus 33 (33P). Detection sensitivity and the desired degree of spatial resolution are the most important factors to consider in choosing which of these radioisotopes to use. Although 32P and 35S will continue to be standard, new uses for 33P will probably soon be developed.