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PCR amplification of DNA can give rise to non-specific products particularly when degenerate primers (2) are employed. The excision and purification of the band of interest from a gel is required to permit further characterisation of the product by direct DNA sequencing, digestion with restriction endonucleases, cloning, mutation detection by SSCP (3), or use as a probe. We have developed a simple method for obtaining and further amplifying a specific single PCR product from a mixture of PCR products of different molecular weight. Specific DNA fragments generated by combined PCR subtraction hybridization (1) and cloned in pUC 18 were used as template for PCR. Each PCR reaction was performed in sterile 0.5 ml tubes using 100 f1l final reaction volumes containing Tris, pH 8.3, 10 mM; KCI, 50 mM; MgCl2, 1.5 mM; gelatin, 0.01%(w/v); dNTP's, 200 AsM; primer (M13), 1 AtM; 0.5 units of AmpliTaq DNA …