Nuclear export of 5S rRNA-containing ribonucleoprotein complexes requires CRM1 and the RanGTPase cycle

Abstract

In Xenopus oocytes, 5S rRNA is exported out of the nucleus in the context of two ribonucleoprotein complexes (RNPs): complexed with transcription factor IIIA as the 7S RNP or as the 5S RNP with ribosomal protein L5. 5S rRNA-containing RNP export takes place at a slow rate in comparison to that of nuclear export signal-containing proteins and the U1 snRNP. Using oocyte microinjection assays we found that the export of 5S RNPs requires nuclear RanGTP and RanGTP hydrolysis and is leptomycin B-sensitive, indicating the process is mediated by the export receptor CRM1. A novel nuclear export signal motif is characterised in a region of L5 also possessing a nuclear import signal, thus identifying a shuttling domain for this protein. This same motif in L5 is found to be required for interaction with CRM1 in vitro and for export in vivo.