Detection of Specific DNA SequencesThe Southern Transfer

The purpose of this technique is the detection and characterization of specific DNA sequences. The DNA is fragmented by digestion with a restriction endonuclease, and the fragments separated by agarose gel electrophoresis. The DNA is then denatured in the gel and transferred to a nitrocellulose filter. This is incubated with a ³² P-labeled probe, which is DNA having a base sequence complementary to the DNA that is to be detected on the filter. After hybridization of the probe to its complementary sequence, unbound probe is washed off. The position of the probe on the filter is then detected by autoradiography. This procedure was developed by E. M. Southern of Edinburgh University (1 ), and is generally referred to as the Southern transfer or Southern blot.