Are viruses alive? Viruses have found an ingenious way of perpetuating themselves, without ever being truly alive.

bacteriophage T4

Unlike most living organisms, they can be frozen or boiled, but then explode into life if conditions are right. Viruses enter other organisms' cells and take over their machinery, making copies of themselves, but they can't "reproduce" on their own.

Using a combination of imaging techniques, researchers have determined that some viruses infect cells by piercing the cells' outer membranes, digesting the walls and injecting virus DNA into the cell. These findings explain how viruses invade cells and offer a new way to deliver genes and drugs directly into cells.

The study, funded by the National Science Foundation's (NSF) Biological Sciences Directorate, was led by researchers Michael Rossman of Purdue University and Vadim Mesyanzhinov of the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry in Moscow. The team studied the structure of the bacteriophage T4—a virus that attacks the familiar microbe E. coli.

Some strains of E. coli live in the human gut where they supply us with essential vitamins. Other strains are famous for causing food poisoning. It’s possible, say scientists, that studies of viruses can help biologists develop strategies to fight deadly bacterial infections. Efforts to use viruses to target antibiotic-resistant bacteria are already underway.

The researchers combined x-ray crystallography, which provides a 3-D picture of the viruses’ proteins, with cryo-electron microscopy images to determine how T4 proteins rearrange themselves during cell infection.

Now that scientists have found out what the relationships are among the T4 component proteins, they’re analyzing other processes that occur during an infection. They’re also studying other viruses to identify the common or distinguishing features of each virus type.

These studies provide hope that engineered viruses might be used to seek out and destroy specific cells or deliver a "payload" that might include new genes or drugs.