TAR RNA DECOYS INHIBIT TAT-ACTIVATED HIV-1 TRANSCRIPTION AFTER PREINITIATION COMPLEX-FORMATION

The ability of the HIV-1 Tat protein to trans-activate HIV-1 transcrip tion in vitro is specifically inhibited by a circular TAR RNA decoy. T his inhibition is not overcome by adding an excess of Tat to the react ion but is partially overcome by adding Tat in combination with nuclea r extract, suggesting that TAR RNA might function by interacting with a complex containing Tat and cellular factor(s). A cell-free transcrip tion system involving immobilized DNA templates was used to further de fine the factor(s) that interact with TAR RNA. Preinitiation complexes formed in the presence or absence of Tat were purified on immobilized templates containing the HIV-1 promoter. After washing, nucleotides a nd radiolabelled UTP were added and transcription was measured. The pr esence of Tat during preinitiation complex formation resulted in an in crease In the level of full-length HIV-1 transcripts. This Tat-activat ed increase in HIV-1 transcription was not inhibited by circular TAR d ecoys added during preinitiation complex formation but was inhibited b y circular TAR decoys subsequently added during the transcription reac tion. These results suggest that TAR decoys inhibit Tat-activated HIV- I transcription after preinitiation complex formation, perhaps by inte racting with components of transcription complexes.