Real-time single-molecule imaging of the infection pathway of an adeno-associated virus

We describe a method, based on single-molecule imaging, that allows the rea l-time visualization of the infection pathway of single viruses in living c ells, each labeled with only one fluorescent dye molecule. The tracking of single viruses removes ensemble averaging. Diffusion trajectories with high spatial and time resolution show various modes of motion of adeno-associat ed viruses (AAV) during their infection pathway into living HeLa cells: (i) consecutive virus touching at the cell surface and fast endocytosis; (il) free and anomalous diffusion of the endosome and the virus in the cytoplasm and the nucleus; and (iii) directed motion by motor proteins in the cytopl asm and in nuclear tubular structures. The real-time visualization of the i nfection pathway of single AAVs shows a much faster infection than was gene rally observed so far.