How are proteins imported into the nucleus?

Question

How are proteins imported into the nucleus?

Answer 1

The nuclear envelope of all eucaryotes is perforated by large, elaborate structures known as nuclear pore complexes.

The selectivity of this nuclear import process resides in nuclear localization signals (NLSs), which are present only in nuclear proteins.

To initiate nuclear import, most nuclear localization signals must be recognized by nuclear import receptors.

The import receptors are soluble cytosolic proteins that bind both to the nuclear localization signal on the protein to be transported and to nucleoporins, some of which form the tentaclelike fibrils that extend into the cytosol from the rim of the nuclear pore complexes

Nuclear import receptors do not always bind to nuclear proteins directly. Additional adaptor proteins are sometimes used that bridge between the import receptors and the nuclear localization signals on the proteins to be transported