Classical Nuclear Localization Signals: Definition, Function, and Interaction with

The best understood system for the transport of macromole-cules between the cytoplasm and the nucleus is the classical nuclear import pathway. In this pathway, a protein containing a classical basic nuclear localization signal (NLS) is imported by a heterodimeric import receptor consisting of the -karyopherin importin , which mediates interactions with the nuclear pore complex, and the adaptor protein importin , which directly binds the classical NLS. Here we review recent studies that have advanced our understanding of this pathway and also take a bioinformatics approach to analyze the likely prevalence of this system in vivo. Finally, we describe how a predicted NLS within aprotein of interest canbe confirmed experimentally to be func-tionally important. In eukaryotic cells, the genetic material and transcriptional machinery of the nucleus are separated from the translationa