Anthramycin inhibition of restriction endonuclease cleavage and its use as a reversible blocking agent in DNA constructions.

Anthramycin can form a stable complex with DNA which does not dissociate upon repeated ethanol precipitations. The complex forms in less than one hour at pH 5.5. Bound anthramycin seems to be located in the minor groove of the DNA helix in the anthramycin DNA complex, since methylation of adenosine residues at N-3 by dimethylsulfate is reduced. The anthramycin-DNA complex is resistant to digestion by an excess of a number of restriction enzymes. Anthramycin can be removed from DNA by incubation at acid pH. The released DNA can then be cleaved by restriction enzymes. Anthramycin-DNA complexes can be acted upon by T4 polynucleotide ligase to form longer DNA molecules. The ability of anthramycin to form a stable but reversible complex which is not cleaved by restriction enzymes but can engage in joining reactions may allow a wider variety of DNA fragments to be more readily constructed in vitro.