Enter the virus

Single-molecule imaging has enabled Christoph Bräuchle, Michael Hallek (Universität München, München, Germany), and colleagues to track the infection pathway of adeno-associated virus (AAV) as it enters the cell. The AAV particles are tagged with a single molecule of fluorophore and are then individually tracked in real-time at a resolution of 40 nm and 10 msec.

The AAV first bobbles along the surface of the cell, often making several contacts before it undergoes a rapid endocytosis event. Most of the motion from there to the nucleus is diffusional, possibly due to the small size and therefore high diffusibility of the virus. There is, however, some directed movement that is microtubule-dependent.

In the nuclear area, the proportion of microtubule-dependent, directed movement actually increases. Microtubules are not known to exist in interphase nuclei, so the authors suggest that the...