Abstract
COLICIN E1 plasmid (colE1) is a closed circular DNA molecule with a molecular weight of 4.2 × 106 (ref. 1). ColE1 DNA has extensively been used as a molecular vehicle for cloning and amplification of DNA in genetic engineering2,3. In order to expand such investigations, it is useful to make a cleavage map ordering colEl DNA pieces produced by bacterial restriction endonucleases. Escherichia coli RI restriction endonuclease (R · EcoRI) has been shown to cleave colE1 DNA at a single unique site4–6. We have now constructed a physical map with the EcoRI site as a reference point using two restriction endonucleases from Haemophilus aegyptius (R · HaeII and R · HaeIII). The map of the colE1 moiety involved in a hybrid plasmid pML21 (ref. 7) carrying about a half of the colEl genome was also determined. Restriction endonucleases and fragments produced by the cleavages were abbreviated as those by Smith and Nathans8. The size of each fragment was expressed as a percentage of the length of the colEl DNA molecule.
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