On the cover, the vault is a ubiquitous cellular particle (420 x 750 A) composed of multiple copies of three proteins and RNA. When the major vault protein is expressed in Sf9 cells, it assembles into vault-like particles and "vaultimers" with multiple half-vaults (for details see the article by Stephen et al, pages 23217-23220). Both types of particles are observed in a negative strain electron micrograph, shown together with a vault cryo-EM reconstruction (Kong, L. B., Siva, A. C., Kickhoefer, V. A., Rome, L. H., and Stewart, P. L. (2000) RNA 6, 890-900). Cover compostion was done by Dr. Phoebe Stewart, UCLA.23217.