Analysis of synergy between divergent simple retrovirus posttranscriptional control elements.

Mason-Pfizer monkey virus (MPMV) and spleen necrosis virus (SNV) are simple retroviruses that encode functionally divergent cis-acting RNA elements that use cellular proteins to facilitate nuclear export and translation of unspliced viral RNA. We tested the hypothesis that a combination of MPMV constitutive transport element (CTE) and SNV or MPMV RU5 translational enhancer on unspliced HIV-1 gag-pol reporter RNA synergistically augments Gag production. Results of transient transfection assays validate the hypothesis of synergistic augmentation in COS cells, but not 293 cells. RNA targeting experiments verified comparable responsiveness to CTE-interactive proteins tethered by RRE and RevM10Tap in COS and 293 cells. Exogeneous expression of Tap and NXT1 was necessary and sufficient to rescue Gag augmentation in 293 cells. Overexpression experiments established that CTE, but not RU5, confers the responsiveness to Tap and NXT1 and that CTE in conjunction with Tap and NXT1 conferred a 30-fold increase in translational utilization of the cytoplasmic RNA. Our results uncovered a previously unidentified role of CTE in conjunction with Tap and NXT1 in commitment to efficient cytoplasmic RNA utilization.