Macromolecular assemblies: greater than their parts.

Increasingly powerful methods of analysis have opened up complex macromolecular assemblies to scrutiny at atomic detail. They reveal not only examples of assembly from preformed and prefolded components, but also examples in which the act of assembly drives changes to the components. In the most extreme of these examples, some of the components only achieve a folded state when the complex is formed. Striking results have appeared for systems ranging from the already mature field of virus structure and assembly, where notable progress has been made for rather complex capsids, to descriptions of ribosome structures in atomic detail, where recent results have emerged at breathtaking speed.