The Interaction between Cap-binding Complex and RNA Export Factor Is Required for Intronless mRNA Export

Abstract

RNA export factor (REF) is a component of the exon junction complex (EJC) that is deposited onIn eukaryotic cells, pre-mRNAs are primarily transcribed by RNA polymerase II (RNAPII); this process is followed by complex RNA processing steps that include capping, splicing, and polyadenylation to produce mature mRNAs. Recent studies have shown that individual events occurring during eukaryotic gene expression are coupled together under more elaborate regulatory controls than previously imagined (1-5). Coupling stimulates the rate and specificity of enzymatic reactions by tethering mechanisms to each other and to their substrates. Following processing, mRNA is exported as a large mRNA-protein complex (mRNP) 2 through the nuclear pore to the cytoplasm for subsequent translation.The transport of mRNA from the nucleus to the cytoplasm is linked to pre-mRNA splicing, especially in metazoans (6). Exon junction complexes (EJCs), which are deposited on mRNAs at specific sites relative to the exon junction as a consequence of splicing, form the basis of this connection (7,8). The EJC consists of four core proteins, eIF4A3 (9 -11), Y14 (7), Magoh (12, 13), and MLN51 (14), plus other auxiliary proteins including REF (7), UAP56 (15), RNPS1 (7), SRm160 (7), Pinin (16, 17), Acinus L (18), SAP18 (18), and hUpf3 (8,19,20). The recruitment of REF during mRNA biogenesis is thought to be responsible for the increased export of spliced mRNA (21). A DEAD box RNA helicase, UAP56, is required for the recruitment of REF to mRNA (15,22). Subsequently, UAP56 is displaced from REF by the mRNA export factor TAP (23). TAP forms a heterodimer with p15 that then directly interacts with the nuclear pore to facilitate mRNP transport into the cytoplasm (24).Although the above model explains the apparent link between splicing and RNA export in metazoans, the question of how intronless mRNAs, which lack EJC deposition, are exported to the cytoplasm naturally arises. Some intronless transcripts (e.g. histone H2A) have been reported to contain specific sequences that recruit export factors independently of splicing (25). SRp20 and 9G8, which belong to members of the evolutionarily conserved SR (serine/arginine-rich) protein family, specifically bind to a sequence in intronless mRNA and greatly facilitate the export of mRNA by recruiting TAP (26). However, the intronless mRNAs coding Ftz, dihydrofolate reductase, and ␤-globin, which lack such cis-acting sequences, can be effectively exported regardless of whether splicing has occurred (27)(28)(29) To clarify the recruiting mechanism of RNPs on mRNAs, we primarily developed a coupled in vitro transcription-splicing system. This in vitro system led us to discover a novel mechanism through which REF can associate with mRNA in a manner that is independent of splicing, instead of via the cap structure

Purification of Nuclear Poly(A)-binding Protein Nab2 Reveals Association with the Yeast Transcriptome and a Messenger Ribonucleoprotein Core Structure

“…Yra1) could bind at several sites along the mRNA. Indeed, it has shown Yra1 is associated with the nascent mRNA transcript from the 5Ј to the 3Ј part (38), and the mammalian Yra1 homologue Aly/Ref and members of the human TREX complex were found to associate with the 5Ј part of the mRNA involving the cap binding complex (39,40).…”

Paraspeckle formation during the biogenesis of long non-coding RNAs

“…During mRNA biogenesis, the mRNA export factors are recruited via the 5' cap structure. 18,19 The mechanism to arrest export factor recruitment may It was determined that paraspeckles are sensitive to RNase treatment after cell permeabilization. 7,8 They suggested that an as-yet-unidentified RNA molecule was required for their structural maintenance.…”

A Novel Role for Cet1p mRNA 5′-Triphosphatase in Promoter Proximal Accumulation of RNA Polymerase II in Saccharomyces cerevisiase

“…The mRNA cap structure consists of a seven-methylguanosine moiety attached to the nascent mRNA via a 59-59 triphosphate linkage. The cap structure recruits cap-binding complex (CBC) that plays crucial roles in maintaining the stability of mRNA and its splicing, export, and translation (Izaurralde et al 1994;Colot et al 1996;Izaurralde et al 1995;Flaherty et al 1997;Schwer et al 1998;Shatkin and Manley 2000;Shen et al 2000;Ishigaki et al 2001;McKendrick et al 2001;Maquat 2004;Gornemann et al 2005;Hosoda et al 2005;Svitkin et al 2005;Balatsos et al 2006;Nojima et al 2007;Wong et al 2007;Kuhn et al 2008;Laubinger et al 2008). Further, CBC has been recently implicated in controlling transcriptional initiation and elongation, histone H2B ubiquitylation, histone H3K36 (lysine 36) methylation, RNA interference, cell proliferation, and processing of primary microRNAs (Kim et al 2008;Gruber et al 2009;Hossain et al 2009Hossain et al , 2013Nielsen et al 2009;Sabin et al 2009;Lahudkar et al 2011;Lidschreiber et al 2013).…”