Binds to intron-containing transcripts and is involved in quality control for the export of spliced mRNAs from the nucleus (PubMed:14676199, PubMed:14769921, PubMed:24452287). Binds to pre-mRNAs until splicing is completed or until faulty mRNAs are degraded. On correctly spliced mRNAs, GBP2 and HRB1 recruit MEX67 to allow nuclear export. On faulty mRNAs, GBP2 and HRB1 associate with the TRAMP complex that guides those pre-mRNAs to the exosome for degradation (PubMed:24452287). Shuttles between nucleus and cytoplasm (PubMed:9499403). Nuclear at steady state and its import is mediated by the karyopherin MTR10. Export is dependent on active transcription and the export of mRNAs in general. Depends on MFT1 and HPR1 for nuclear export (PubMed:14676199). Methylated by HMT1. Present with 1990 molecules/cell in log phase SD medium.