Nancy Kedersha purified enough vaults to carry out studies to analyze their building blocks. The vaults were separated into their component parts using a common method called SDS-PAGE. With this method the individual parts of the vault are separated on a gel. The gel can be stained to reveal the individual parts of the vault. An example of such a stained gel is shown at the right. The gel had 5 major bands indicating that the vault is made up of 5 different sized building blocks.
Four of these bands are proteins (labelled 240, 193, 100, and 54 in the figure to the right) and the fifth band is an RNA (labelled 37). Because it is composed of protein and RNA, a vault is classified as a ribonucleoprotein particle or RNP for short. Vaults turn out to be one of the largest RNPs known.
The most abundant protein in vaults is the protein labeled 100 in the gel. The 100 refers to the size of the protein in thousands of Daltons (a Dalton is a chemical unit for size). A protein of 100 thousand Daltons would be expected to be made up of about 800 amino acids. This protein makes up over 70% of the particle and is therefore referred to as MVP (for Major Vault Protein).
The vault RNA (called vRNA) is an integral component of the vault particle. The sequence of the vRNA was identified by Drs. Valerie Kickhoefer and Robert Searles. Dr Kickhoefer also isolated the gene that codes for the vRNA.
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