They have been around since the dawn of time and are a model of evolutionary¹ success: viruses. Viruses are extremely adaptable² but they have a problem: They cannot reproduce, so they smuggle³（走私，偷运） their genes⁴ into suitable host cells. In the case of some viruses, the viral DNA⁵ has to enter the cell nucleus⁶ to reproduce. This has been known for almost 50 years. We know, for instance, that the adenovirus（腺病毒） disassembles its protein shell in the first step. Just how the DNA is exposed and infiltrates⁷ the host cell, however, remained unclear despite decades of research. A research group headed by Urs Greber, a cell biologist at the University of Zurich, has now managed to clear up these points. As the scientists recently revealed in the journal Cell Host & Microbe, viruses use the cell's own mechanisms⁸. The adenovirus latches⁹ onto a gatekeeper molecule¹⁰, which sits on the nuclear pore complex in the nucleus envelope and controls the passage in and out of the nucleus. Another protein in the nuclear pore complex binds¹² and activates¹³ a motor protein from the kinesin（驱动蛋白） family, which regulates the transport of substances near the nucleus.

Virus DNA uncoated with aid of host cell

"The motor protein is in an active condition, can bind¹¹ to micro-tubules and migrate along them," says Professor Greber, explaining his team's observations. And the docked virus uses precisely¹⁴ this situation for its purposes. The virus binds to the kinesin and uses the energy of the motor to disrupt its own shell, which exposes the virus DNA and prepares it for transport into the nucleus. The action of the activated¹⁵ motor has another effect, too: The nuclear pore ruptures¹⁶ and becomes markedly bigger, which enables the viral DNA to enter the cell nucleus more easily. Surprisingly, the cell repairs the defective¹⁷ nuclear pore so that the virus breach¹⁸ in the nucleus does not leave any visible damage in its wake. The viral DNA is smuggled¹⁹ into the nucleus practically without trace, where it can reproduce easily.

The researchers used adenoviruses for their study. Adenoviruses cause, among other things, respiratory（呼吸的） or epidemic²⁰ ocular disease. Until recently, they were thought to be relatively²¹ harmless for healthy humans. However, the results of another research group recently demonstrated that a new kind of adenovirus triggered a dreaded²² zoonotic（动物传染病的） disease, meaning it was transmitted from an animal to humans before spreading from one person to another.