Visualization of viral assembly in the infected cell

The study of the virus life cycle in infected cells is a methodological cha llenge due to the small size and diversity of the viral components. Recent developments on preservation of fine structure and molecular localization h ave provided a group of powerful methods with wide applications in cell bio logy and virology. Among the different electron microscopy (EM) techniques available to visualize viral assembly at the intracellular level, we will f ocus on conventional ultrathin sections, cryosections, and freeze-substitut ion. For obtaining molecular information associated to ultrastructure we ha ve now a group of methods to detect viral proteins (immunogold labeling), a s well as the viral genome, through the different techniques for detection of nucleic acids (the enzyme-gold approach, in situ hybridization, and elem ental mapping). We will illustrate the applications of these methods with e xamples of viruses that exhibit different levels of structural complexity. These new approaches help to detect and identify viruses in clinical sample s and to characterize the virus life cycle and the cellular components invo lved, to obtain data that could help for a therapeutic intervention, and to characterize virus-like particles that can be the basis of new and safe va ccines.