The 5 ' RNA terminus of spleen necrosis virus contains a novel posttranscriptional control element that facilitates human immunodeficiency virus Rev/RRE-independent Gag production

Previous work has shown that spleen necrosis virus (SNV) long terminal repe ats (LTRs) are associated with Rex/Rex-responsive element-independent expre ssion of bovine leukemia virus RNA and supports the hypothesis that SNV RNA contains a cl-acting element that interacts with cellular Rex-like protein s. To test this hypothesis, the human immunodeficiency virus type 1 (HIV) R ev/RRE-dependent gag gene was used as a reporter to analyze various SNV seq uences. Gag enzyme-linked immunosorbent assay and Western blot analyses rev eal that HIV Gag production is enhanced at least 20,000-fold by the 5' SNV LTR in COS, D17, and 293 cells. Furthermore, SNV RU5 in the sense but not t he antisense orientation is sufficient to confer Rev/RRE-independent expres sion onto a cytomegalovirus-gag plasmid. In contrast, the SNV 3' LTR and 3' untranslated sequence between env and the LTR did not support Rev-independ ent gag expression. Quantitative RNase protection assays indicate that the SNV 5' RNA terminus enhances cytoplasmic accumulation and polysome associat ion of HIV unspliced and spliced transcripts. However, comparison of the ab solute amounts of polysomal RNA indicates that polysome association is not sufficient to account for the significant increase in Gag production by the SNV sequences. Our analysis reveals that the SNV 5' RNA terminus contains a unique cis-acting posttranscriptional control element that interacts with hypothetical cellular Rev-like proteins to facilitate HIV RNA transport an d efficient translation.