Yeast Enzyme Shown to Cut DNA Precisely at RNA-DNA Junctions

Karwan and Wintersberger, writing in FEBS Letters in 1986, describe how a yeast enzyme cuts a hybrid molecule made of RNA and DNA at a very specific point. This is a laboratory biochemistry study, not a medical or skin study.

The researchers built a synthetic test molecule — a strand of M13 viral DNA paired with a stretch of RNA joined to radioactively labeled DNA — to see exactly how an enzyme called RNase H(70), isolated from the yeast Saccharomyces cerevisiae, breaks down such mixed molecules. RNase H enzymes normally degrade RNA when it is paired with DNA, a key step in processes like DNA replication.

The study found that RNase H(70) cuts the chemical bond precisely at the junction where the RNA segment meets the DNA segment. This produces a DNA fragment, a polydeoxyribonucleotide, with a phosphate group on one end, and a separate RNA fragment with a hydroxyl group on the other end.

As an abstract-only report of a single enzymatic reaction in a test tube, the study says nothing about how this enzyme behaves in living cells, nor anything about effects in tissue, skin, or whole organisms.