The C-terminal domain of TAP interacts with the nuclear pore complex and promotes export of specific CTE-bearing RNA substrates

Abstract

Messenger RNAs are exported from the nucleus as large ribonucleoprotein complexes (mRNPs). To date, proteins implicated in this process

Mutations in Tap Uncouple RNA Export Activity from Translocation through the Nuclear Pore Complex

“…Tap can bind a number of nucleoporins in vitro including p62, Can/ Nup214, Nup98, RanBP2, and CG1 (Katahira et al, 1999;Bachi et al, 2000;Lévesque et al, 2001;Katahira et al, 2002;Grant et al, 2003;Forler et al, 2004). Using a solid-phase binding assay, we have observed that Nxt1 could stimulate binding of both cargo-free Tap and the Tap/CTE RNA complex to p62 .…”

“…Tap also mediates nuclear export of certain retroviral mRNAs, such as the Mason-Pfizer monkey virus (MPMV; Grü ter et al, 1998). A cis-acting element in the noncoding 3Ј region of these viral transcripts, known as the constitutive transport element (CTE), forms a stem-loop structure recognized by Tap (Bray et al, 1994;Ernst et al, 1997aErnst et al, , 1997bGrü ter et al, 1998;Braun et al, 1999;Bachi et al, 2000;Liker et al, 2000). In contrast, the interaction between Tap and eukaryotic mRNAs appear to require a number of adaptor proteins that are recruited to messenger ribonucleoprotein (mRNP) complexes during transcription and processing (Izaurralde, 2002;Cullen, 2003;Stutz and Izaurralde, 2003;Vinciguerra and Stutz, 2004).…”

A natural allele of Nxf1 suppresses retrovirus insertional mutations

“…While one cannot actually prove selection from a retrospective analysis of a single region, several features of the data are suggestive. S48 sits in a poorly conserved region of Nxf1 that is not essential to Nxf1 biochemical function 23 . In contrast, E610 is highly conserved among vertebrates and sits in a UBA domain thought to mediate nuclear export through physical interaction with the nuclear pore and exhibits a significant chemical shift upon binding FG peptide 24,25 (Figure 5b-d).…”

Expression of the essential mRNA export factor Yra1p is autoregulated by a splicing-dependent mechanism

“…Prior to their export into the cytoplasm, the primary transcripts of protein-encoding eukaryotic genes (premRNAs) require extensive processing into mRNAs, including the removal of intronic sequences and the addition of a cap structure to the 59 end and a poly(A) tail to the 39 of the transcript+ Presumably, cells have evolved mechanisms to coordinate these processing events to improve the efficiency of each step and to ensure that only fully and correctly processed transcripts are translated into protein+ Early evidence for a coupling between splicing and downstream events came from the observation that the presence of an intron promotes expression of trans-genes in metazoan cells (Matsumoto et al+, 1998)+ More recently, this effect has been attributed to an enhancement in the rate of export of mRNAs that have undergone splicing, relative to mRNAs derived from non-intron-containing genes (Luo & Reed, 1999)+ In the same study, it was proposed that the increased export efficiency was due to assembly of the mRNA with specific RNA-binding proteins as a result of splicing+ Shortly thereafter, the identification of a multiprotein complex, referred to as the exon-junction complex (EJC) was reported+ This complex is deposited in a sequence-independent, but position-specific manner ;20 nt upstream of exon-exon junctions concomitant with, or immediately following, in vitro splicing (Le Hir et al+, 2000)+ The EJC was suggested to serve as a marker for properly spliced and thus export-competent mRNAs+ Consistent with this notion, one of the components was identified as Aly (also known as REF), a small RNAbinding protein implicated in mRNA export in metazoans (Le Hir et al+, 2000;Stutz et al+, 2000;Zhou et al+, 2000)+ Aly/REF directly interacts with the conserved mRNA export factor TAP (Stutz et al+, 2000)+ TAP in turn interacts with components of the nuclear pore complex, the site of transport of macromolecules between the nucleus and the cytoplasm (Kang & Cullen, 1999;Bachi et al+, 2000)+ As expected for a bona fide mRNA export carrier, TAP continuously shuttles between these two compartments (Bear et al+, 1999)+ Another link between pre-mRNA splicing and export was uncovered when UAP56, a factor originally implicated in spliceosome assembly, was subsequently shown to be also required for efficient mRNA export (Gatfield et al+, 2001;Luo et al+, 2001)+ UAP56 is a member of the DEAD-box family of ATPases+ These enzymes have been demonstrated to promote changes in RNA-RNA and, more recently, RNA-protein interactions that drive multistep reactions such as translation, pre-mRNA splicing, and ribosomal RNA processing (for review, see Staley & Guthrie, 1998;Linder et al+, 2001)+ Strikingly, in vitro experiments demonstrated that UAP56 can interact directly with Aly, and that association of UAP56 with newly spliced mRNA can be detected prior to Aly in time-course experiments (Luo et al+, 2001)+ In addition, mutant forms of Aly that are unable to...…”