SnapShot: Formation of mRNPs

• Multiple adaptor proteins (e.g., Yra1/Aly/REF1 and SR proteins) drive mRNP export by loading dimeric export receptor (Mex67-Mtr2/TAP-p15/NXF1-NXT1).• In yeast, TREX complex recruited to polymerase; DECD helicase Sub2 loads Yra1 onto mRNA. In vertebrates, TREX binds cap via splicing-dependent interaction of Aly/REF1(vertebrate Yra1) with CBP80.• Export coupled to transcription via SAGA chromatin-remodeling complex, which binds TREX2 and relocates some genes to nuclear pore for export.• Export coupled to 3′ end processing (TREX required for 3′ end formation and release of mRNP from transcription site).• Different export adaptors or receptors confer transcript specifi city, e.g., TREX is important for export of heat-shock gene transcripts. • Transit through pore via binding of Mex67/TAP/NXF1 to nucleoporin FG repeats.• mRNP remodeled on cytoplasmic side of pore by Dbp5 DEAD-box helicase (which is activated by Gle1 and inositol phosphate).