Yeast Shuttling SR Proteins Npl3p, Gbp2p, and Hrb1p Are Part of the Translating mRNPs, and Npl3p Can Function as a Translational Repressor

Abstract

A major challenge in current molecular biology is to understand how sequential steps in gene expression are coupled. Recently, much attention has been focused on the linkage of transcription, processing, and mRNA export. Here we describe the cytoplasmic rearrangement for shuttling mRNA binding proteins in Saccharomyces cerevisiae during translation. While the bulk of Hrp1p, Nab2p, or Mex67p is not associated with polysome containing mRNAs, significant amounts of the serine/arginine (SR)-type shuttling mRNA binding proteins Npl3p, Gbp2p, and Hrb1p remain associated with the mRNA-protein complex during translation. Interestingly, a prolonged association of Npl3p with polysome containing mRNAs results in translational defects, indicating that Npl3p can function as a negative translational regulator. Consistent with this idea, a mutation in NPL3 that slows down translation suppresses growth defects caused by the presence of translation inhibitors or a mutation in eIF5A. Moreover, using sucrose density gradient analysis, we provide evidence that the import receptor Mtr10p, but not the SR protein kinase Sky1p, is involved in the timely regulated release of Npl3p from polysomeassociated mRNAs. Together, these data shed light onto the transformation of an exporting to a translating mRNP.

Restraint of the G2/M Transition by the SR/RRM Family mRNA Shuttling Binding Protein SNXAHRB1 in Aspergillus nidulans

“…Hrb1/ Gbp2 associate both with the genes and the growing, unprocessed mRNA transcripts produced from them and remain bound to the mRNA transcripts as part of the messenger RNA-protein complex (mRNP). As shuttling proteins, Hrb1/ Gbp2 remain bound to the transcript during export from the nucleus; they also remain associated with the mRNP during 618 S. W. James et altranslation (Windgassen et al 2004). et al 2014).…”

Structure of the C-terminus of the mRNA export factor Dbp5 reveals the interaction surface for the ATPase activator Gle1

“…A recent study has indicated that Dbp5 can function to remodel RNA-protein interactions in vitro because it is able to promote the dissociation of Nab2 from a Nab2-RNA complex (15). Nab2 associates with polyadenylated RNA but is not found associated with polysomes, indicating that it dissociates from poly(A) RNA before translation (21)(22)(23). Additionally, in vivo cross-linking studies have shown that reduced Dbp5 activity correlates with an increase in both Mex67 and Nab2 association with poly(A) RNA in vivo, consistent with the hypothesis that removal of these proteins from RNA is an in vivo function of Dbp5 (15,24).…”

The SR Protein 9G8 and the Wilms' Tumor Suppressor Protein WT1 Promote Translation of mRNAs with Retained Introns

“…This model suggests that the effects of SR proteins on translation might be regulated by SR protein kinases as well as proteins involved in nuclear reimport. A recent study by Krebber and collaborators showed that the Npl3p protein associates with yeast polysomes (209). Based on genetic experiments, they proposed that Mtr10p, the import receptor for Npl3p, might be involved in a timely regulated release of Npl3p from the polysomes.…”

“…Similar experiments could also be performed for over-expressed Transportin SR, which is the import receptor for the SR proteins. In yeast studies, it was found that Mtr10p (the yeast homologue of Transportin SR) was important for the release of Npl3p (the SR protein homologue) from polysome-associated mRNAs, but the Sky1p (the kinase homologue) was not important (209). It would be of interest to determine how closely the mammalian system mimics the yeast system.…”