Nature would never leave something as valuable as genetic code unprotected. One of the security measures protecting DNA in plants and animals is a mechanism that fights viruses by shutting down their genes. In plants the phenomenon is known as gene silencing, and it has been widely used to study plant genes. It has also been used to create transgenic tomato plants that are resistant to plant viruses.

What works in tomatoes may also work in people. A number of laboratories are investigating ways to exploit the naturally occurring defense mechanism in humans to fight HIV, the virus that causes AIDS. A new study reports success in blocking the virus in cell cultures by silencing genes in HIV and human cells.