Cell Enzyme Can Join RNA to DNA Using a DNA Template

Bedows and colleagues, writing in Biochemistry in 1977, showed that an enzyme called DNA ligase, taken from mouse L cells, can chemically link a piece of RNA to a piece of DNA — but only when both are lined up on a matching strand of polydeoxyribonucleotide, a synthetic DNA-like template.

The researchers worked entirely in a test tube, not in living cells or animals. They built short synthetic DNA and RNA fragments, labeled them with a radioactive marker, and tied them together on template strands made of repeating DNA letters (poly[d(T)] and poly[d(C)]). Using enzyme treatments and chemical tests, they confirmed the new bond really joined RNA to DNA rather than just sealing two DNA pieces. This "mixed" joining happened, but much less efficiently than the ligase's normal job of stitching DNA to DNA. Some combinations of fragments, despite being tried, could not be joined at all.

Because this is a cell-free biochemical experiment, it cannot say anything about how this joining reaction behaves inside a living cell, nor about any biological or medical effect. It is a study of enzyme mechanism and chemistry, not of therapy or physiology.