Southern blot

A standard method of analyzing the structure of DNA cleaved by restriction endonucleases. The fragments of DNA are subsequently separated by size by gel electrophoresis. The DNA fragments are then denatured to separate the two strands of DNA. The single-strand DNA molecules are then blot transferred from the gel on to the surface of a solid-phase filter which is an opposed nitrocellulose or nylon membrane. The membrane serves as a lattice to capture and bind the single strands of DNA. After the DNA is heat-fixed to the membrane, the specific DNA sequence can be identified by incubating the filter with a single strand of radioactive DNA (called the probe) complementary to the recombinant DNA sequence of interest. The resulting hybridized labeled DNA:DNA complex, which is bonded to the nitrocellulose/nylon framework, is developed on an X-ray film to identify the original DNA fragments.