| Here , we show that the INS region in HIV 1 gag mRNA is a high affinity ligand of p54nrb / PSF , a heterodimeric transcription / splicing factor . ^^^ Using an INS containing subgenomic gag mRNA , we show that it specifically associated with p54nrb in vivo and that PSF inhibited its expression , acting via INS . ^^^ Studying the authentic HIV 1 mRNAs produced from an infectious molecular clone , we found that PSF affected specifically the INS containing , Rev dependent transcripts encoding Gag Pol and Env . ^^^ Thus , p54nrb and PSF have properties of key factors mediating INS function and likely define a novel mRNA regulatory pathway that is hijacked by HIV 1 . . ^^^ |