Description: nuclear import and export, Mechanism of Nuclear Transport | RAN GTPase Cycle, The Nuclear Pore Complex: Nuclear Import, Export, & RAN, Ran GTPase Cycle and Nuclear Transport | Importins and Exportins, Protein Export Through the Nuclear Pore Complex
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A nuclear localization signal or sequence ( NLS ) is an amino acid sequence that 'tags' a protein for import into the cell nucleus by nuclear transport . Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal , which targets proteins out of the nucleus.
Classical NLSs can be further classified as either monopartite or bipartite. The first NLS to be discovered was the sequence PKKKRKV in the SV40 Large T-antigen (a monopartite NLS). The NLS of nucleoplasmin, KR[PAATKKAGQA]KKKK, is the prototype of the ubiquitous bipartite signal: two clusters of basic amino acids, separated by a spacer of about 10 amino acids. Both signals are recognized by importin α . Importin α contains a bipartite NLS itself, which is specifically recognized by importin β. The latter ca
The entry and exit of large molecules from the cell nucleus is tightly controlled by the nuclear pore complexes (NPCs). Although small molecules can enter the nucleus without regulation,[1] macromolecules such as RNA and proteins require association with transport factors like karyopherins called importins to enter the nucleus and exportins to exit. Protein that must be imported to the nucleus from the cytoplasm carry nuclear localization signals (NLS) that are bound by importins. A NLS is a sequence of ami