Vaults are microscopic structures found in nearly all cells which have a nucleus. They were first seen in 1986 using electron microscope 'negative staining' techniques.(ref.)

They are highly regular in structure, made of specialsed proteins, and with a strict 36-fold symmetry (Illustration here) The hollow barrel-like structures typically have a length of approximately 70 nm and a diameter of 40 nm.

They have so far been found in the cells of mammals, birds, fish, plants, nematodes, yeasts, bacteria etc. etc.. Many cells have have a vault count of over 10,000.

Their function is not presently known.

Given their prevalence, it's assumed that they could have some critical cellular function(s) - possibly involving intra-cellular transport processes.- which go far back in evolutionary time.

Further technical details :Structure of the vault, a ubiquitous cellular component Structure, Vol.7(4), p.371-379

Vaults are one example of the large number of cellular 'organelles' which have yet-to-be-identified functions. See : Cellular organellesplugin-autotooltip__plain plugin-autotooltip_bigCellular organelles

Eukaryotic cells are cells which have a nucleus. Within that nucleus are various discrete structures with very specific functions that are, as a group, called 'organelles'.

In the 1970s a book by professor Lynn Margulis (titled Origin of Eukaryotic Cells)