Purα as a cellular co-factor of Rev/RRE-mediated expression of HIV-1 intron-containing mRNA

To ensure successful replication, HIV-1 has developed a Rev-mediated RNA transport system that promotes the export of unspliced genomic RNA from nuclei to cytoplasm. This process requires the Rev responsive element (RRE) that is positioned in the viral transcript encoding Env protein, as well as in unspliced and singly spliced viral transcripts. We identified Pur alpha, a single-stranded nucleic acid binding protein as a cellular partner for Rev that augments the appearance of unspliced viral RNAs in the cytoplasm. A decrease in the level of Pura expression by siRNA diminishes the level of Rev-dependent expression of viral RNA. Through its nucleic acid binding domain, Pura exhibits the ability to interact with the multimerization and RBD domains of Rev. Similar to Rev, Pura associates with RRE and in the presence of Rev forms a complex with slower electrophoretic mobility than those from Rev:RRE and Pura:RRE. The interaction of Pura with RRE occurs in the cytoplasm where enhanced association of Rev with RRE is observed. Our data indicate that the partnership of Pura with Rev is beneficial for Rev-mediated expression of the HIV-1 genome.