Scientists image a single HIV particle ...(ating the entire cell. But when that bea...),Health

Date:5/25/2008

ating the entire cell. But when that beam is brought to a steeper angle, the lights energy reflects off the cells surface, illuminating only the events going on at its most outer membrane. By zeroing in at the cells surface, the team became the first to document the time it takes for each HIV particle, or virion, to assemble: five to six minutes. At first, we had no idea whether it would take milliseconds or hours, says Jouvenet. We just didnt know.

This is the first time anyone has seen a virus particle being born, says Bieniasz, who is an associate professor and head of the Laboratory of Retrovirology at Rockefeller and a scientist at the Aaron Diamond AIDS Research Center. Not just HIV, he clarifies, any virus.

To prove that what they were watching was virus particles assembling at the surface (rather than an already assembled virion coming into their field of view from inside the cell), the group tagged a major viral protein, called the Gag protein, with molecules that fluoresce, but whose color would change as they packed closer together. Although many different components gather to form a single virion, the Gag protein is the only one necessary for assembly. It attaches to the inner face of the cells outer membrane and when enough Gag molecules flood an area, they coalesce in a way that spontaneously forms a sphere.

Simon, Bieniasz and Jouvenet found that the Gag molecules are recruited from the inside of the cell and travel to the cells surface. When enough Gag molecules get close and start bumping into each other, the cells outer membrane starts to bulge outward into a budding virion and then pinches off to form an individual, infectious particle. At this point, the researchers showed that the virion is a lone entity, no longer exchanging resources with the cell. By using tricks from optics and physiology, they were able to watch the steps of viral assembly, budding, and even scission off the cell surface. With such a view they c
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Contact: Thania Benios tbenios@rockefeller.edu 212-327-7146 Rockefeller University Source:Eurekalert

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