According to Harrison, when HIV enters a human cell, it uses RT and RNA to form a new strand of viral DNA. Then this strand is used to make another one,which when joined with the first, forms the fameddouble helix.

Researchers pinpointed a moment in the encodingof the second strand of viral DNA at which one newbuilding block of DNA, known as a nucleotide, isadded.

"What we wanted to do was get a snapshot in aparticular stage of the reaction cycle," Harrisonsaid. "In other words, trap the enzyme in action."

The moment at which a nucleotide is added isimportant because it is the same instant at whichmany HIV drugs inhibit RT--or fail to, if RT hasmutated.

RT inhibitors attempt to act as a stop valve,inserting defective nucleotides that are unable tobind with other molecules, thus ending the growthof a new chain of DNA and preventing thereproduction of HIV.

Getting a freeze frame of the mechanism was anextremely difficult task because of the alarmingrate at which HIV grows, Harrison said.

Huang was the one who found a way to look atthe molecules for only an instant.

"If you're a child who cannot sit still youbasically bind this child to a chair," Huang said.

Developing a model of the structure of themolecule at the particular instant was also madepossible by X-ray crystallography--Chopra'sspecialty--which provided the necessary data.

The model the researchers built of RT--placedon computer generated diagrams--resembles a handmoving along a stand of DNA.

All of this research is important not only forsolving the riddle of HIV, but also for purelyscientific reasons, Harrison said. The work willhelp scientists understand how enzymes such asRT--called polymerases--work "in general," henoted.

Huang said it is difficult to quantify howsignificant the new work is, but he said that itsappearance in Science places it at the forefrontof scientific research.

Only one or two pure research articles areplaced in the magazine each week, he added. "Theyhave limited space," Huang noted. "[The research]must be pretty good."

Ho said he has not yet read the article, but hepraised the group of researchers. "I just knowthat group generally does beautiful work and I'vesure they've done the same," he said.

What Now?

Though new AIDS drugs could mean a mountain ofmoney, Huang said he and his fellow researcherswill probably not be involved in drug development.