Isolation of a novel rmn1 gene genetically linked to spnab2 with respect to mRNA export in fission yeast.

In fission yeast, Schizosaccharomyces pombe, the spnab2 gene encodes an ortholog of the budding yeast nuclear abundant poly(A)(+) RNA-binding protein 2 (Nab2) that is an essential protein required for both mRNA biogenesis and nuclear export of mRNA to the cytoplasm. We have previously isolated three mutants (SLnab1-3) that showed synthetic lethality under the repressed condition of spnab2 expression. In this study, we isolated a novel rmn1 gene as a multicopy suppressor that complemented the defects in growth and mRNA export of SLnab1 mutant cells. The rmn1 gene contained three introns and encoded a 589 amino-acid protein with the RNA recognition motif (RRM) in the central region. The Δrmn1 null mutant was viable but showed a s light mRNA export defect. However, its over-expression caused a deleterious effect on growth accompanied by intense accumulation of poly(A)(+) RNA in the nucleus. The combination of Δrmn1 with Δspnab2 or Δspmex67 also inhibited growth. In addition, Rmn1p was associated with Rae1p in vivo. These results suggest that rmn1 is a novel gene that is functionally linked to spnab2.