Preparation of milligram amounts of 21 deoxyribonucleic acid restriction fragments

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Abstract
Twenty-one DNA restriction fragments ranging in size from 12 to 880 base pairs (bp) were purified to homogeneity in milligram amounts. The developments which facilitated this work were procedures for the rapid preparation of gram quantities of pure recombinant plasmid DNA, selective polyethylene glycol (PEG) precipitation of DNA according to broad classes of lengths, and large-scale high-pressure liquid chromatography on RPC-5 for the purification of fragments to homogeneity. The 95- and 301-bp sequences from the lactose control region of Escherichia coli were cloned into the single EcoRI site of pVH51 in up to 4 copies per plasmid. These tandem inserts are separated by EcoRI sites and have a head to tail orientation in all cases. A total of 50 and 90 mg of the 95- and 301-bp fragments, respectively, were prepared from 300-l fermentations of E. coli cells transformed with these plasmids. A rapid and improved method, which can easily be scaled up, for the purification of plasmids and DNA restriction fragments was developed. Also, the linear pVH51 vector DNA was digested with HaeIII to yield fragments ranging in size from 12-880 bp. The 5 smaller fragments (from 12-180 bp) were purified quantitatively by a selective PEG precipitation enrichment step followed by RPC-5 column fractionation. The larger fragments (245-880 bp) were prepared in milligram amounts. Ten subfragments from the 301-bp lac fragment were prepared by HpaII, Hinfl or HaeIII/AluI digestions followed by separation of the reaction products on RPC-5.