HIV-1 Cis Enhancing Sequence (CES) enhances CTE-dependent Gag expression

In order to export intron-containing RNA from nucleus, retroviruses use either viral trans-acting factors or constitutive cellular factors interacting with cis-elements in their intron-containing RNA. We have previously identified a Cis Enhancing Sequence (CES) in HIV-1 env region that could co-operate with Rev and RRE to enhance Gag expression by promoting RNA stabilization and exportation. In this study, we found that CES could function in a Rev-independent manner by co-operating with a Constitutive Transport Element (CTE) of Mason-Pfizer monkey viruses (MPMV). RRE and CTE promote intron-containing RNA exportation through different pathways. The fact that CES could function in both pathways of RNA export suggested that CES might function at a common step either up- or downstream to Rev/RRE or CTE functions. Known hnRNP-A1-binding sites as well as other 3 highly conserved sequences in the CES were found to be required for its activity.