- Vault (organelle)
The vault or vault cytoplasmic ribonucleoprotein is a recently discovered
eukaryotic organelleof which its function is not yet well known. Discovered and successfully isolated by biochemist Leonard Romeof the UCLASchool of Medicine in the 1980s, vaults are cytoplasmic organelles which resemble a barrel, with eight-fold symmetry. They are present in many types of eukaryotic cells and appear to be highly conserved amongst eukaryotesKedersha, N. L., Miquel, M. C., Bittner, D. and Rome, L. H. (April 1990). "Vaults. II. Ribonucleoprotein structures are highly conserved among higher and lower eukaryotes." J. Cell Biol. 110, 895-901.] .
Vaults are large
ribonucleoproteinparticles. About 3 times the size of a ribosomeand weighing approximately 13 MDa, they are found in many diverse eukaryotic cells. They measure 34 nm by 60 nm from a negative stain, 26 nm by 49 nm from cryo-electron microscopy, and 35 nm by 59 nm from STEM [Kedersha, N. L., Heuser, J. E., Chugani, D. C. and Rome, L. H. (1991). "Vaults. III. Vault ribonucleoprotein particles open into flower-like structures with octagonal symmetry." J. Cell Biol. 112, 225-235.] . The vaults consist primarily of proteins, making it difficult to stain with conventional techniques. The protein structure consists of many major vault proteins (MVP) bound to one of the two minor vault proteins. Two large complexes of several MVP's and a minor vault protein close together to form the barrel-like vault organelle. They may contain small RNAs of 86–141 bases within [A. van Zon, M. H. Mossink, R. J. Scheper, P. Sonneveld1 and E. A. C. Wiemer. "The vault complex" Cellular and Molecular Life Sciences (CMLS), Volume 60, Number 9, September, 2003; p 1828-1837] .
Despite not being fully elucidated, vaults have been associated with the
nuclear pore complexes and their octagonal shape appears to support this [Unwin, P. N. T. and Milligan, R. A. (1982). "A large particle associated with the perimeter of the nuclear pore complex." J. Cell Biol. 93, 63-75.] . It has been concluded that the vault's function is the transportation of molecules, such as mRNA, from the nucleus to parts of the cytoplasm[Diane C. Chugani, Leonard H. Rome and Nancy L. Kedersha. "Evidence that vault ribonucleoprotein particles localize to the nuclear pore complex" Journal of Cell Science 106, 23-29 (1993)] . It is also thought that vaults play a role in protein synthesis[Cindy L. Stanfield, William J. Germann "Principles of Human Physiology: Third Edition" Pearson Education Inc. 2008; p 41] .
Association with cancer
In the late 1990s, researchers found that vaults (especially the MVP) were over-expressed in
cancerpatients who were diagnosed with multidrug resistance, that is the resistance against many chemotherapytreatments [Marieke H Mossink, Arend van Zon, Rik J Scheper, Pieter Sonneveld and Erik AC Wiemer. "Vaults: a ribonucleoprotein particle involved in drug resistance?" Oncogene (2003) 22, 7458–7467. doi:10.1038/sj.onc.1206947] . Although this does not prove that increased number of vaults led to drug resistance, it did hint some sort of involvement. This has potential in discovering the mechanisms behind drug-resistance in tumor cells and improving anticancer drugs [Valerie A. Kickhoefer, Sanjay K. Vasu and Leonard H. Rome "Vaults are the answer, what is the question?" Trends in Cell Biology Volume 6, Issue 5, May 1996, Pages 174-178] .
Extent of ubiquitous nature
Although vaults have been observed in many eukaryotic species, a few species do not appear to have the protein. These include [Leonard Rome, Nancy Kedersha and Diane Chugani. "Unlocking vaults: organelles in search of a function." Trends in Cell Biology Volume 1, Issues 2-3, August-September 1991, Pages 47-50.] :
Arabidopsis" - a small flowering plant related to cabbage and mustard.
Caenorhabditis elegans" - a free-living nematode that lives in soil.
Drosophila melanogaster" - a two-winged insect also known as a fruit fly.
Saccharomyces cerevisiae" - a species of yeast.
Albeit these exceptions, the high degree of similarity between organisms that do have vaults implies some sort of evolutionary importance.
Major vault protein
* [http://www.vaults.arc.ucla.edu/ Vault website (UCLA)]
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