320 mRNA turnover Philip Mitchell* and David Tollervey† Nuclear RNA-binding proteins can record pre-mRNA are cotransported to the cytoplasm with the mRNP. These processing events in the structure of messenger proteins may preserve a record of the nuclear history of the ribonucleoprotein particles (mRNPs). During initial rounds of pre-mRNA in the cytoplasmic mRNP structure. This infor- translation, the mature mRNP structure is established and is mation can strongly influence the cytoplasmic fate of the monitored by mRNA surveillance systems. Competition for the mRNA and is used by mRNA surveillance systems that act cap structure links translation and subsequent mRNA as a checkpoint of mRNP integrity, particularly in the identi- degradation, which may also involve multiple deadenylases. fication of premature translation termination codons (PTCs). Addresses Cotransport of nuclear mRNA-binding proteins with mRNA Wellcome Trust Centre for Cell Biology, ICMB, University of Edinburgh, from the nucleus to the cytoplasm (nucleocytoplasmic shut- Kings’ Buildings, Edinburgh EH9 3JR, UK tling) was first observed for the heterogeneous nuclear *e-mail:
[email protected] ribonucleoprotein (hnRNP) proteins. Some hnRNP proteins †e-mail:
[email protected] are stripped from the mRNA at export [1], but hnRNP A1, Current Opinion in Cell Biology 2001, 13:320–325 A2, E, I and K are all exported (see [2]). Although roles for 0955-0674/01/$ — see front matter these hnRNP proteins in transport and translation have been © 2001 Elsevier Science Ltd. All rights reserved. reported [3•,4•], their affects on mRNA stability have been little studied. More is known about hnRNP D/AUF1 and Abbreviations AREs AU-rich sequence elements another nuclear RNA-binding protein, HuR, which act CBC cap-binding complex antagonistically to modulate the stability of a range of DAN deadenylating nuclease mRNAs containing AU-rich sequence elements (AREs) DSEs downstream sequence elements (reviewed in [2]).