Using DNA fragments as probes.

All hybridization methods depend upon the ability of denatured DNA to reanneal when complementary strands are present in an environment near but below their Tm (melting temperature). A detailed procedure is described in which bacteriophage plaques or bacterial colonies bound to a filter membrane are detected by hybridization with a radioactive probe. Hybridization proceeds on prewet filters placed in a sealable plastic bag. After hybridization the filters are removed from the sealed bag, excess probe is washed off, and the filters are autoradiographed to identify the clones that have hybridized with the probe. An Alternate Protocol differs mainly in that formamide is not used in the hybridization solution.