[5][6] 78 copies of the protein assemble into the large compartments called vaults.

It is widely distributed in normal tissues and overexpressed in multidrug-resistant cancer cells.

The protein overexpression is a potentially useful marker of clinical drug resistance.

[6] Major vault protein coimmunoprecipitates with the human estrogen receptor and treatment with estradiol increases major vault protein associated with the estrogen receptor in nuclear extracts.

[8] Major vault protein has been shown to interact with estrogen receptor alpha,[9] PTEN[10] and PARP4.