Putative nuclear localization signals (NLS) in protein transcription factors

AbstractWe have recognized about ten distinct forms of strongly basic hexapeptides, containing at least four arginines and lysines, characteristic of nuclear proteins among all eukaryotic species, including yeast, plants, flies and mammals. These basic hexapeptides are considered to be different versions of a core nuclear localization signal, NLS. Core NLSs are present in nearly all nuclear proteins and absent from nearly all “nonassociated” cytoplasmic proteins that have been investigated. We suggest that the few (∼ 10%) protein factors lacking a typical NLS core peptide may enter the nucleus via their strong crosscomplexation with their protein factor partners that possess a core NLS. Those cytoplasmic proteins found to possess a NLS‐like peptide are either tightly associated with cell membrane proteins or are integral components of large cytoplasmic protein complexes. On the other hand, some versions of core NLSs are found in many cell membrane proteins and secreted proteins. It is hypothesized that in these cases the N‐terminal hydrophobic signal peptide of extracellular proteins and the internal hydrophobic domains of transmembrane proteins are stronger determinants for their