Evidence that a consensus element found in naturally intronless mRNAs promotes mRNA export

摘要

We previously showed that mRNAs synthesized from three genes that naturally lack introns contain a portion of their coding sequence, known as a cytoplasmic accumulation region (CAR), which is essential for stable accumulation of the intronless mRNAs in the cytoplasm. The CAR in each mRNA is unexpectedly large, ranging in size from ~160 to 285 nt. Here, we identified one or more copies of a 10-nt consensus sequence in each CAR. To determine whether this element (designated CAR-E) functions in cytoplasmic accumulation of intronless mRNA, we multimerized the most conserved CAR-E and inserted it upstream of p-globin cDNA, which is normally retained/degraded in the nucleus. Significantly, the tandem CAR-E, but not its anti-sense counterpart, rescuedcytoplasmic accumula-ion of p-globin cDNA transcripts. Moreover, linucleotide mutations in the CAR-E abolished this escue. We show that the CAR-E, but not the mutant )AR-E, associates with components of the TREX iRNA export machinery, the Prp19 complex and I2AF2. Moreover, knockdown of these factors ssults in nuclear retention of the intronless lRNAs. Together, these data suggest that the AR-E promotes export of intronless mRNA by equence-dependent recruitment of the mRNA icport machinery.