Figure 1.

RNA splicing and nuclear RNA export are functionally linked. A pre-mRNA, whether transcribed in vivo or microinjected into the nucleus, is recognized by splicing commitment factors that both function as nuclear retention factors (RF) and initiate the process of mRNA splicing. As shown by Luo and Reed (3), completion of mRNA splicing results not only in the removal of these retention factors but also in the recruitment of nuclear export factors (EF) that target the resultant mature mRNA to the cytoplasm. In contrast, a microinjected mRNA lacking any intron (Δi-mRNA) is exported only very inefficiently, apparently because export factor recruitment is also inefficient. SD, splice donor; SA, splice acceptor.