Trans-activation response element

The trans-activation response element is an RNA element which is known to be required for the trans-activation of the HIV promoter and for HIV replication. The HIV TAR hairpin is a dynamic structure that acts as a binding site for the Tat protein, and this interaction stimulates the activity of the long terminal repeat promoter.
Further analysis has shown that HIV TAR is a pre-microRNA that produces mature microRNAs from both strands of the TAR stem-loop.
These miRNAs are thought to prevent infected cells from undergoing apoptosis by downregulating the genes ERCC1, IER3, CDK9, and Bim.
Human polyomavirus 2 contains a TAR-homologous sequence in its late promoter that is responsive to HIV-1 derived Tat.