Yra1p is an essential and conserved mRNA export factor in yeast. Strikingly, removal of the intron from YRA1 causes a dominant-negative growth phenotype and a concomitant inhibition of mRNA export. However, both defects are neutralized by replacement of the intron of YRA1 by a different intron. Significantly, Yra1p is overproduced in yeast when expressed from its intronless gene, but Yra1p levels are the same as the wild type when expressed from an intron-containing YRA1 gene. Thus, an intron in YRA1 controls Yra1p expression and mRNA export.