Abstract
Macromolecular complexes, rather than individual biopolymers, perform many cellular activities. Faithful assembly of these complexes in vivo is therefore a vital challenge of all cells, and its failure can have fatal consequences. To form functional complexes, cells use elaborate measures to select the "right" components and combine them into working entities. How assembly is achieved at the molecular level is unclear in many cases. Three groups (Jin and colleagues, pp. 2391-2403; Xu and colleagues, pp. 2376-2390; and Tang and colleagues in Cell Research) have now provided insights into how an assembly factor specifically recognizes substrate RNA molecules and enables their usage for assembly of Sm-class uridine-rich small nuclear RNA-protein complexes.