HIV Rev-dependent binding of SF2/ASF to the Rev response element: Possible role in Rev-mediated inhibition of HIV RNA splicing

Production of the structural and enzymatic proteins of type 1 human immunodeficiency virus (HIV-1) is controlled by therev regulatory gene product. The 116-amino acid Rev protein acts by binding to the Rev response element (RRE), a complex RNA stem–loop structure located within theenv gene of HIV. Rev exerts a series of posttranscriptional effects, including the inhibition of viral RNA splicing, the activation of nuclear export of incompletely spliced viral RNAs, and the enhancement of translation of RRE-containing RNAs. Our studies now demonstrate that at least one member of the SR family of splicing factors, SF2/ASF, specifically binds to a subregion of the RREin vitro in a Rev-dependent manner. Furthermore, expression of high levels of SF2/ASF inhibits Rev function and impairs HIV replicationin vivo . Both thein vitro binding of SF2/ASF to the Rev/RRE complex and thein vivo inhibition of Rev action by SF2/ASF are abrogated by mutation of the N-terminal RNA recognition motif but are not affected by mutation of the C-terminal arginine–serine-rich domain. These findings suggest that Rev inhibition of HIV splicing likely involves recruitment of the essential splicing factor SF2/ASF to the Rev/RRE complex. However, these inhibitory effects of Rev on viral RNA splicing are apparently overcome by augmenting the intracellular levels of SF2/ASF expression.