Abstract: An important step in mRNA biogenesis is the export of mRNA from the nucleus to the cytoplasm. In this work, we provide evidence that the previously uncharacterized gene APQ12 functions in nucleocytoplasmic mRNA transport in Saccharomyces cerevisiae. First, apq12delta strains manifest 3' hyperadenylated mRNA similar to other previously characterized RNA export mutants. Second, bulk poly(A)+ RNA is retained in the nucleus in apq12delta cells. Third, an Apq12p-GFP chimeric protein is localized to the nuclear periphery. Fourth, mRNA in apq12delta cells is stabilized, consistent with a defect in the rate of nuclear export. Interestingly, apq12delta mutants are severely compromised for growth and display atypical cell morphology. Because this aberrant cell morphology is not seen with other viable export mutants, Apq12p must have either an additional cellular function, or preferentially impinge on the export of mRNAs regulating cell growth. Together, these findings support a role for APQ12 in nucleocytoplasmic transport of mRNA.