Swiss microbial geneticist, Werner Arber shared the 1978 Nobel Prize in Physiology or Medicine with Hamilton Smith and Daniel Nathans for their discovery of restriction endonucleases. Arber found that viral DNA introduced into a non-specific bacterial host was changed, while host DNA was protected by methylation. He theorized that a microbial enzyme cut the DNA into smaller pieces, while at the same time, the methylated host DNA was protected from its own enzymes. Later work done by Nathans and Smith validated his theory, which laid the foundation for recombinant DNA technology.