Photoactivatable Antisense DNA: Suppression of Ampicillin Resistance in Normally Resistant Escherichia coli

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Abstract
Antisense oligodeoxyribonucleotides complementary to a segment of the β-lactamase gene and containing psoralen monoadducts at specific sites were examined for their ability to make normally resistant bacteria sensitive to ampicillin. Irradiation of oligonucleotides and psoralens with long-wavelength ultraviolet radiation (380–400 nm) produced monoadducted antisense molecules. High-performance liquid chromatography was used to purify microgram quantities of photoactivatable antisense DNA. Escherichia coli transformed with a plasmid containing the gene for β-lactamase were used to test a series of oligonucleotides containing psoralen monoadducts after additional exposure to the photoactivating effects of long-wavelength ultraviolet radiation (320–400 nm). Normally resistant bacteria treated with this photoactivatable form of antisense DNA (0.4 μM) were specifically sensitized to ampicillin. The reduction in colony formation ranged from 31 to 79% in comparison to control oligonucleotides which did not contain photoactivatable monoadduct moieties. Bacteria treated in a similar manner but in the presence of tetracycline instead of ampicillin were not affected. The activity of β-galactosidase, whose gene is located on the same plasmid as β-lactamase, was not affected.