Abstract: A method of extracting a particular nucleic acid fragment containing a nucleic acid sequence of interest from a nucleic acid or nucleic acids mixture, comprising the steps of:(1) digesting the nucleic acid or nucleic acids mixture with restriction enzymes to obtain a mixture of nucleic acid fragments, said restriction enzymes consisting of (A) two different enzymes capable of producing the particular nucleic acid fragment bearing predetermined and distinct restriction ends on its 5' and 3' terminals and (B) one or more restriction enzymes different from (A), for which the particular nucleic acid fragment contains no relevant restriction sites;(2) preparing two distinct DNA linkers capable of binding to the respective restriction ends of the particular nucleic acid fragment;(3) allowing the linkers to react with the mixture of nucleic acid fragments;(4) subjecting the resulting reaction mixture to the first hybridization with an immobilized probe complementary to one of the linkers;(5) isolating the hybridized