Strongmen of the viral world
Molecular motor packs DNA into viruses at pressures many timesgreater than that in a champagne bottle, researchers report

By Robert Sanders, Public Affairs

Spiral DNA, at the upper right, is being packed into a bacteriophage at pressures ten times greater than those in a champagne bottle. Image by Paul Thiessen (Chemical Graphics)

31 October 2001 | The DNA inside some viruses is packed so tightly that the internal pressure reaches ten times that in a champagne bottle, according to new measurements by biophysicists at Berkeley and the University of Minnesota.

The researchers suspect that this high pressure helps the virus spurt its DNA into a cell once it has latched onto the surface. Once the DNA gets inside, it begins retooling the cell to manufacture new viruses. The process eventually kills the cell, but not before generating thousands more viruses to spread the infection.

Such tight packing is achieved by one of the most powerful molecular motors ever observed, stronger than the motors that move our muscles or the nanoscale molecular motors that duplicate DNA or transcribe it into RNA.

“Pound for pound, this is stronger than any known molecular motor, and can pack DNA to a pressure of about 60 atmospheres,” said biophysicist Carlos Bustamante, professor of physics and of molecular and cell biology in the College of Letters & Science. A bottle of champagne typically is under pressure of five to six atmospheres, the equivalent of nearly one hundred pounds per square inch.

“Many human viruses, such as the herpes viruses that cause herpes simplex, chicken pox and shingles, are thought to pack their DNA in the same way,” said Bustamante, “so understanding how this process works could help us design better drugs to interfere with the packing part of the infection cycle of the virus, and perhaps halt infection.”

Bustamante and his colleagues - former Berkeley postdocs Douglas Smith and Sander Tans, research associate Steven Smith, and scientists from the University of Minnesota - report their findings in the Oct. 18 issue of Nature.

Bustamante is a member of Berkeley’s Health Sciences Initiative, a broad effort bringing together researchers from many disciplines to work on health problems of the 21st century, and a researcher in the Howard Hughes Medical Institute and Lawrence Berkeley National Laboratory.