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

Abstract

Eukaryotic cells have to prevent the export of unspliced pre-mRNAs until intron removal is completed to avoid the expression of aberrant and potentially harmful proteins. Only mature mRNAs associate with the export receptor Mex67/TAP and enter the cytoplasm. Here we show that the two shuttling serine/arginine (SR)-proteins Gbp2 and Hrb1 are key surveillance factors for the selective export of spliced mRNAs in yeast. Their absence leads to the significant leakage of unspliced pre-mRNAs into the cytoplasm. They bind to pre-mRNAs and the spliceosome during splicing, where they are necessary for the surveillance of splicing and the stable binding of the TRAMP complex to spliceosome-bound transcripts. Faulty transcripts are marked for their degradation at the nuclear exosome. On correct mRNAs the SR proteins recruit Mex67 upon completion of splicing to allow a quality controlled nuclear export. Altogether, these data identify a role for shuttling SR proteins in mRNA surveillance and nuclear mRNA quality control.

Rapid identification of mRNA processing defects with a novel single-cell yeast reporter

“…4A-C), which primarily result from an increase in GFP. Mlp1p has been shown to mediate retention of unspliced reporter mRNAs, resulting in increased premRNA reporter translation in its absence (Galy et al 2004;Hackmann et al 2014), which is in contrast with the result shown here. Although both reporters are weakly spliced due to suboptimal intron architecture, our reporter contains the extended 3 ′ UTR that is efficiently degraded in the cytoplasm via NMD (Fig.…”

“…Of note, we also observe a similar effect in cells lacking the SR-like protein Gbp2 (Fig. 4E), which was recently shown to be involved with Mlp1p in a potential mRNP quality control mechanism coupled with export (Hackmann et al 2014).…”

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

“…As suggested by Rougemaille et al (2008), Hrb1/Gbp2 may act as dedicated adaptors that recognize specific sets of transcripts. Hackmann et al (2014) recently demonstrated that Hrb1/ Gbp2 function both to recognize and to mediate the elimination of aberrantly spliced transcripts via binding to Mtr4 and to mediate the nuclear export of correctly spliced transcripts via Mex67 (Hackmann et al 2014).Given that the A. nidulans Hrb1 homolog, snxA, was identified as a genetic interactor with nimX cdc2 and that the snxA1 mutation arrests cells in G1 at its restrictive temperature, it is possible that SNXA HRB1 interacts with cell cycle-specific transcripts or proteins. The SR/RRM family has not previously been implicated in the regulation of the G2/M transition.…”

“…As suggested by Rougemaille et al (2008), Hrb1/Gbp2 may act as dedicated adaptors that recognize specific sets of transcripts. Hackmann et al (2014) recently demonstrated that Hrb1/ Gbp2 function both to recognize and to mediate the elimination of aberrantly spliced transcripts via binding to Mtr4 and to mediate the nuclear export of correctly spliced transcripts via Mex67 (Hackmann et al 2014).…”

“…In addition to their functions in mRNA transcription and export, SR-like proteins act as localization signals that aid in delivering the mRNP to the translational machinery (Windgassen et al 2004). More recently, both Hrb1 and Gbp2 have been shown to associate with the budding yeast spliceosome (Warkocki et al 2009), with unspliced transcripts close to 59 intron sequences (Tuck and Tollervey 2013), and with intron sequences and splicing factors (Hackmann et al 2014).…”