Structure of the vault, a ubiquitous cellular component

Background: The vault is a ubiquitous and highly conserved ribonucleoprotei n particle of approximately 13 MDa. This particle has been shown to be upre gulated in certain multidrug-resistant cancer cell lines and to share a pro tein component with the telomerase complex. Determination of the structure of the vault was undertaken to provide a first step towards understanding t he role of this cellular component in normal metabolism and perhaps to shed some light on its role in mediating drug resistance. Results: Over 1300 particle images were combined to calculate an approximat ely 31 Angstrom resolution structure of the vault. Rotational power spectra did not yield a clear symmetry peak, either because of the thin, smooth wa lls or inherent flexibility of the vault. Although cyclic eightfold (C8) sy mmetry was imposed, the resulting reconstruction may be partially cylindric ally averaged about the eightfold axis. Our results reveal the vault to be a hollow, barrel-like structure with two protruding caps and an invaginated waist. Conclusions: Although the normal cellular function of the vault is as yet u ndetermined, the structure of the vault is consistent with either a role in subcellular transport, as previously suggested, ol in sequestering macromo lecular assemblies.