Most proteins require karyopherins to traverse the nuclear pore.

But some proteins require being folded in particular ways or having sugars added before they can be used.

Almost all cellular proteins require eIF4E in order to be translated into protein.

Also some cellular proteins, the most notable being heat shock proteins, do not require eIF4E in order to be translated.

Also, careful selection of the fluorescent protein is important, as different fluorescent proteins require different cellular environments.

Some proteins require post-translative modifications.

This is because protein folding requires entropic cost.

Some intrinsic proteins require a fluid environment for their activity, while others operate in a fixed, immobile, condition.

In bread making with rye flour, this protein requires exposure to an acid such as lactic acid so that the bread will rise.

However, in the majority of cases proteins will require the presence of molecular chaperons within the cell for proper folding.