Nonclassical nuclear localization signals mediate nuclear import of CIRBP

Proc Natl Acad Sci U S A. 2020 Apr 14;117(15):8503-8514. doi: 10.1073/pnas.1918944117. Epub 2020 Mar 31.


The specific interaction of importins with nuclear localization signals (NLSs) of cargo proteins not only mediates nuclear import but also, prevents their aberrant phase separation and stress granule recruitment in the cytoplasm. The importin Transportin-1 (TNPO1) plays a key role in the (patho-)physiology of both processes. Here, we report that both TNPO1 and Transportin-3 (TNPO3) recognize two nonclassical NLSs within the cold-inducible RNA-binding protein (CIRBP). Our biophysical investigations show that TNPO1 recognizes an arginine-glycine(-glycine) (RG/RGG)-rich region, whereas TNPO3 recognizes a region rich in arginine-serine-tyrosine (RSY) residues. These interactions regulate nuclear localization, phase separation, and stress granule recruitment of CIRBP in cells. The presence of both RG/RGG and RSY regions in numerous other RNA-binding proteins suggests that the interaction of TNPO1 and TNPO3 with these nonclassical NLSs may regulate the formation of membraneless organelles and subcellular localization of numerous proteins.

Keywords: CIRBP; Transportin-1; Transportin-3; nuclear import; phase separation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus
  • Arginine / chemistry
  • Arginine / metabolism
  • Cell Nucleus / metabolism*
  • Cytoplasm / metabolism
  • Glycine / chemistry
  • Glycine / metabolism
  • HeLa Cells
  • Humans
  • Nuclear Localization Signals*
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism*
  • Protein Binding
  • Protein Conformation
  • RNA-Binding Proteins / chemistry
  • RNA-Binding Proteins / metabolism*
  • Serine / chemistry
  • Serine / metabolism
  • Tyrosine / chemistry
  • Tyrosine / metabolism
  • beta Karyopherins / chemistry
  • beta Karyopherins / metabolism*


  • CIRBP protein, human
  • Nuclear Localization Signals
  • Peptide Fragments
  • RNA-Binding Proteins
  • TNPO1 protein, human
  • TNPO3 protein, human
  • beta Karyopherins
  • Tyrosine
  • Serine
  • Arginine
  • Glycine