Ubiquitin-mediated mRNP dynamics and surveillance prior to budding yeast mRNA export

Abstract

The evolutionarily conserved mRNA export receptor Mex67/NXF1 associates with mRNAs through its adaptor, Yra1/REF, allowing mRNA ribonucleoprotein (mRNP) exit through nuclear pores. However, alternate adaptors should exist, since Yra1 is dispensable for mRNA export in Drosophila and Caenorhabditis elegans. Here we report that Mex67 interacts directly with Nab2, an essential shuttling mRNA-binding protein required for export. We further show that Yra1 enhances the interaction between Nab2 and Mex67, and becomes dispensable in cells overexpressing Nab2 or Mex67. These observations appoint Nab2 as a potential adaptor for Mex67, and define Yra1/REF as a cofactor stabilizing the adaptor-receptor interaction. Importantly, Yra1 ubiquitination by the E3 ligase Tom1 promotes its dissociation from mRNP before export. Finally, loss of perinuclear Mlp proteins suppresses the growth defects of Tom1 and Yra1 ubiquitination mutants, suggesting that Tom1-mediated dissociation of Yra1 from Nab2-bound mRNAs is part of a surveillance mechanism at the pore, ensuring export of mature mRNPs only.[Keywords: Mex67/NXF1; Nab2; Yra1/REF; Tom1; mRNA export; ubiquitination] Supplemental material is available at http://www.genesdev.org.

Quality control of spliced mRNAs requires the shuttling SR proteins Gbp2 and Hrb1

“…34,35). It seems likely that every maturation step is controlled, in this case the 3 0 -end processing step, and that the passage of each maturation 'checkpoint' might be labelled with the addition of one or more Mex67 molecules.…”

The Ubiquitin–Proteasome System of Saccharomyces cerevisiae

“…A relevant target of Tom1 appears to be Yra1, an adaptor protein linking mRNA to Mex67 (Iglesias et al 2010). Monoubiquitylation and K48-diubiquitylation of Yra1 do not induce proteolysis, but promote dissociation from the Mex67-mRNP complex, which facilitates mRNA export.…”

A new regulatory pathway of mRNA export by an F-box protein, Mdm30

“…Indeed, previous studies (Duncan et al 2000;Neumann et al 2003;Rodriguez et al 2003;Gwizdek et al 2005;Iglesias et al 2010) have demonstrated the direct roles of two HECT domain-containing E3 ubiquitin ligases, namely Tom1 and Rsp5, in mRNA export in yeast. Recently, we have demonstrated that Mdm30, an F-box protein, is also involved in stimulation of nuclear export of mRNA in yeast Shukla et al 2009).…”