The mRNA export factor Npl3 mediates the nuclear export of large ribosomal subunits.

The nuclear export of large ribonucleoparticles is complex and requires specific transport factors. Messenger RNAs are exported through the RNA-binding protein Npl3 and the interacting export receptor Mex67. Export of large ribosomal subunits also requires Mex67; however, in this case, Mex67 binds directly to the 5S ribosomal RNA (rRNA) and does not require the Npl3 adaptor. Here, we have discovered a new function of Npl3 in mediating the export of pre-60S ribosomal subunit independently of Mex67. Npl3 interacts with the 25S rRNA, ribosomal and ribosome-associated proteins, as well as with the nuclear pore complex. Mutations in NPL3 lead to export defects of the large subunit and genetic interactions with other pre-60S export factors.