Vault RNA

Many eukaryotic cells contain large ribonucleoprotein particles in the cytoplasm known as vaults. The vault complex comprises the major vault protein (MVP), two minor vault proteins (VPARP and TEP1), and a variety of small untranslated RNA molecules. Given the association with the nuclear membrane and the location within the cell, vaults are thought to play roles in intracellular and nucleocytoplasmic transport processes. Also, given that the structure and protein composition are highly conserved among species, it is believed that the roles vault plays are integral to eukaryotic function. Many eukaryotic cells contain large ribonucleoprotein particles in the cytoplasm known as vaults. The vault complex comprises the major vault protein (MVP), two minor vault proteins (VPARP and TEP1), and a variety of small untranslated RNA molecules. Given the association with the nuclear membrane and the location within the cell, vaults are thought to play roles in intracellular and nucleocytoplasmic transport processes. Also, given that the structure and protein composition are highly conserved among species, it is believed that the roles vault plays are integral to eukaryotic function. While vault proteins appear to be present in a variety of organisms, vaults isolated from higher eukaryotes contain a small portion, about 5%, of small untranslated RNAs called vault RNAs, or vtRNAs. These RNA molecules are polymerase III transcripts. In addition, a study, using cryo-electron microscopy, has determined that vtRNAs are found close to the end caps of vaults. This positioning of the RNA indicates that they could interact with both the interior and exterior of the vault particle. Overall, the current belief is that the vtRNAs do not have a structural role in the vault protein, but rather play some kind of functional role. However, while there has been an expanding body of research on vtRNA, there has yet to be a solid conclusion on the exact function. Vault RNA was first identified as part of the vault ribonucleoprotein complex in 1986. Since the first discovery of non-coding RNA in the mid 60’s, there had been considerable interest in the field. The fruition of this interest was apparent in the 80’s during a string of non-coding RNA discoveries, such as Ribosomal RNA, snoRNA, Xist, and vault RNA. Early research in the 1990s looked into the specifics of vault RNA and focused around the conservation of the gene in animals. So far vault RNAs have been isolated from humans, rodents and bullfrogs. Vault proteins, but not the vtRNA, have also been found in sea urchin, Dictyostelium discoideum and Acanthamoeba.