Enzymatic mutation detection: enrichment of heteroduplexes from hybrid DNA mixtures by cleavage-deficient GST-tagged endonuclease VII

A method for the enrichment of heteroduplex DNAs from hybrid DNA mixtures by endonuclease VII is reported. The procedure is based on the ability of a GST-fused cleavage-deficient mutant endonuclease VII (EVII-N62D(GST)) to bind to mismatching nucleotides in heteroduplex DNAs identical to the wild-type enzyme. The GST tag was used for stable immobilisation of the protein to Glutathione Sepharose 4B. This enables the material to withstand the repeated rounds of binding steps required for enrichment of heteroduplex molecules from appropriate samples.