Abstract: The present invention pertains to a process for isolating an intact clone of one target nucleic acid fragment having a known characteristic, from a group of fragments by preparing an initial library of clones from the group of fragments using a vector containing no more than a predetermined number of known restriction sites, preferably 1–3 restriction sites, subjecting the initial library to at least 10, and preferably between 50 and 70 restriction enzymes different from those to which the vector is susceptible, to produce a group of monodigested libraries, screening the group of monodigested libraries for the target fragment to determine those restriction enzymes to which the target fragment is insensitive, and subjecting the initial library to substantially all of the restriction enzymes to which the target fragment is insensitive, to produce a multidigested library having an intact clone of the target nucleic acid fragment.