But what those particles do once they are inside -- in particular, how they arrive at the nucleus to hijack the cell's genetic machinery and begin reproducing their own DNA -- had remained a mystery.
The tiny particles, only about 12 millionths of a centimeter in diameter, have to cross a distance that is up to 500 times their size to reach the nucleus. Moreover, the way is blocked by all kinds of cellular structures, from energy-generating mitochondria to packets of proteins. How do the particles get through this obstacle course?
The researchers were able to visualize individual HIV particles by attaching green fluorescent protein to one of their components. Derived from jellyfish, the protein has only recently been discovered as a means of tagging individual molecules inside a living cell. When blue light shines on the protein, it gives off a green glow.
The researchers also made the microtubules of the host cells glow a deep red by incorporating another fluorescent protein into their building blocks.
Pictures of living cells infected with HIV were taken under a microscope at intervals as short as 15 seconds, creating a movie of the viruses' activities as they traversed the microtubular highway toward their destination in the nucleus.
"They don't make a beeline for the nucleus," McDonald said. "Their progress is somewhat halting. They appear to jump from one microtubule to another, moving in a jagged path, even sometimes moving backward. But they eventually reach their destination."
The journey to the nucleus takes about two to four hours, he said.
At the periphery of the nuclei, the scientists saw the viruses form complexes with genetic material of the host cells -- appropriating the tools that HIV needs to reproduce.
Dynein's role was confirmed by injecting an off-the-shelf antibody into the cells that prevents the molecular motors from working. When the motors stop, the vi
'"/>
Contact: Sharon Butler
sbutler@uic.edu
312-355-2522
University of Illinois at Chicago
11-Dec-2002