Bacterial Enzyme Found to Strip Radiation-Damaged Fragments from DNA

Breimer and Lindahl, writing in Nucleic Acids Research in 1980, describe an enzyme from the bacterium E. coli that recognizes and removes a specific type of DNA damage linked to radiation exposure. This is a laboratory biochemistry study, not a skin or medical study, and it does not involve animals or humans.

The researchers first built a synthetic polydeoxyribonucleotide, a lab-made chain of DNA building blocks, using an enzyme called terminal deoxynucleotidyltransferase. They then treated it with a chemical, potassium permanganate, which converted the thymine building blocks into urea and related broken fragments while leaving the adenine building blocks intact. Pairing this damaged strand with a matching one created a double-stranded DNA molecule carrying scattered, radioactively tagged lesions.

When this damaged DNA was mixed with crude extracts from E. coli cells, an enzyme activity released free urea from the broken sites. The researchers partly purified this enzyme, called a DNA glycosylase, and report it has a molecular weight of roughly 20,000 to 25,000, requires no additional helper molecules, and strongly favors double-stranded over single-stranded DNA. Because ionizing radiation commonly produces this kind of fragmented base damage, the authors propose the enzyme helps repair X-ray-induced DNA injuries. The findings come only from bacterial, test-tube experiments and do not show whether a comparable process occurs in animals or people.