Yeast poly(A)-binding Protein Pab1 Shuttles Between the Nucleus and the Cytoplasm and Functions in mRNA Export

RNA. 2005 Apr;11(4):517-31. doi: 10.1261/rna.7291205.


Pab1 is the major poly(A)-binding protein in yeast. It is a multifunctional protein that mediates many cellular functions associated with the 3'-poly(A)-tail of messenger RNAs. Here, we characterize Pab1 as an export cargo of the protein export factor Xpo1/Crm1. Pab1 is a major Xpo1/Crm1-interacting protein in yeast extracts and binds directly to Xpo1/Crm1 in a RanGTP-dependent manner. Pab1 shuttles rapidly between the nucleus and the cytoplasm and partially accumulates in the nucleus when the function of Xpo1/Crm1 is inhibited. However, Pab1 can also be exported by an alternative pathway, which is dependent on the MEX67-mRNA export pathway. Import of Pab1 is mediated by the import receptor Kap108/Sxm1 through a nuclear localization signal in its fourth RNA-binding domain. Interestingly, inhibition of Pab1's nuclear import causes a kinetic delay in the export of mRNA. Furthermore, the inviability of a pab1 deletion strain is suppressed by a mutation in the 5'-3' exoribonuclease RRP6, a component of the nuclear exosome. Therefore, nuclear Pab1 may be required for efficient mRNA export and may function in the quality control of mRNA in the nucleus.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Active Transport, Cell Nucleus
  • Cell Nucleus / metabolism*
  • Cytoplasm / metabolism*
  • Karyopherins / metabolism
  • Nuclear Proteins / metabolism
  • Nucleocytoplasmic Transport Proteins / metabolism
  • Poly(A)-Binding Protein I / deficiency
  • Poly(A)-Binding Protein I / genetics
  • Poly(A)-Binding Protein I / metabolism*
  • RNA, Fungal / metabolism*
  • RNA, Messenger / metabolism*
  • RNA-Binding Proteins / metabolism
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • Saccharomyces cerevisiae Proteins / metabolism
  • Yeasts / genetics
  • Yeasts / metabolism*


  • Karyopherins
  • MEX67 protein, S cerevisiae
  • Nuclear Proteins
  • Nucleocytoplasmic Transport Proteins
  • Poly(A)-Binding Protein I
  • RNA, Fungal
  • RNA, Messenger
  • RNA-Binding Proteins
  • Receptors, Cytoplasmic and Nuclear
  • SXM1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • exportin 1 protein