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 im munodeficiency virus (HIV-1) is controlled by the rev regulatory gene product. The 116-amino acid Rev protein acts by binding to the Rev res ponse element (RRE), a complex RNA stem-loop structure located within the env gene of HIV. Rev exerts a series of posttranscriptional effect s, including the inhibition of viral RNA splicing, the activation of n uclear export of incompletely spliced viral RNAs, and the enhancement of translation of RRE-containing RNAs. Our studies now demonstrate tha t at least one member of the SR family of splicing factors, SF2/ASF, s pecifically binds to a subregion of the RRE in vitro in a Rev-dependen t manner. Furthermore, expression of high levels of SF2/ASF inhibits R ev function and impairs HIV replication in vivo. Both the in vitro bin ding of SF2/ASF to the Rev/RRE complex and the in vivo inhibition of R ev action by SF2/ASF are abrogated by mutation of the N-terminal RNA r ecognition motif but are not affected by mutation of the C-terminal ar ginine-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 effec ts of Rev on viral RNA splicing are apparently overcome by augmenting the intracellular levels of SF2/ASF expression.