Capturing the HIV virus on film.

• Position: Cellular Biology

In stunning color images using time-lapse microscopy, scientists at the University of Illinois at Chicago for the first time have captured the very earliest stages of HIV infection in living cells. The researchers filmed individual HIV particles as they traveled to the nucleus of a human cell and began taking over its genetic machinery--the first step in the destruction of the body's immune system that leads to AIDS.

The movies not only offer tantalizing glimpses of HIV in action, but provide visual proof that HIV enlists the assistance of its host to wreak havoc on the body's defenses. The virus can be seen traveling along a part of the host cell's skeletal framework of microtubules as it makes its way from the outer membrane to the nucleus. The virus hitches a ride aboard a multiunit protein called dynein, commonly referred to as a molecular motor. "Dynein is like a tractor trailer; the microtubules are the highway; and the HIV particles are the cargo," notes David McDonald, assistant professor of microbiology and immunology.

Until recently, little was known about how HIV enters a cell. The virus is made of an outer shell, or envelope, and a core, referred to as a particle, which is composed of proteins and genetic material. When the virus attacks an immune cell, it fuses with the cell's membrane and releases its particle core inside. Yet, 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...