Human immunodeficiency virus type 1 Rev function requires continued synthesis of its target mRNA.

Synthesis of human immunodeficiency virus structural proteins is dependent on expression of the virus-encoded Rev protein due to the constitutive nuclear sequestration of mRNAs coding for the structural proteins. The pathway by which Rev, through interaction with the Rev-responsive element (RRE) within the mRNA, achieves export of the mRNA remains unclear. To probe the mechanism by which Rev induces nuclear export of its target mRNAs, the effect of inhibiting mRNA synthesis on the function of Rev was examined. Two approaches to address this issue were pursued: (i) the use of general transcription inhibitors such as 5,6-dichlorobenzimidazole riboside (DRB) and actinomycin D, and (ii) the more selective modulation of target gene transcription permitted by the use of a tetracycline-regulated promoter. Addition of either DRB or actinomycin D inhibited Rev action despite the presence of significant quantities of the target mRNA throughout the course of drug treatment. Furthermore, prolonged DRB treatment was found to improve rather than diminish the induction observed. Subsequent analysis using the tetracycline-modulated promoter demonstrated that Rev function was dependent on the transcription rate of the target mRNA and independent of target mRNA concentration. These data strongly indicate that Rev functions through interaction with newly synthesized target mRNA, facilitating its export by preventing its interaction with the host factors that effect nuclear sequestration.