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Updated: Aug 7, 2026

High Throughput In Vitro Assessment of Latency Reversing Agents on HIV Transcription and Splicing
Published on: January 22, 2019
A second exon splicing silencer within human immunodeficiency virus type 1 tat exon 2 represses splicing of Tat mRNA
S Jacquenet1, A Méreau, P S Bilodeau
1Laboratoire de Maturation des Acide Ribo-Nucléotidique et Enzymologie Moléculaire, Unité Mixte de Recherche 7567 Université Henri Poincarré-CNRS, Boulevard des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy cedex, France.
Abstract:
An equilibrium between spliced and unspliced primary transcripts is essential for retrovirus multiplication. This equilibrium is maintained by the presence of inefficient splice sites. The A3 3'-splice site of human immunodeficiency virus type I (HIV-1) is required for Tat mRNA production. The infrequent utilization of this splice site has been attributed to the presence of a suboptimal polypyrimidine tract and an exonic splicing silencer (ESS2) in tat exon 2 approximately 60 nucleotides downstream of 3'-splice site A3. Here, using site-directed mutagenesis followed by analysis of splicing in vitro and in HeLa cells, we show that the 5' extremity of tat exon 2 contains a second exonic splicing silencer (ESS2p), which acts to repress splice site A3. The inhibitory property of this exonic silencer was active when inserted downstream of another HIV-1 3'-splice site (A2). Protein hnRNP H binds to this inhibitory element, and two U-to-C substitutions within the ESS2p element cause a decreased hnRNP H affinity with a concomitant increase in splicing efficiency at 3'-splice site A3. This suggests that hnRNP H is directly involved in splicing inhibition. We propose that hnRNP H binds to the HIV-1 ESS2p element and competes with U2AF(35) for binding to the exon sequence flanking 3'-splice site A3. This binding results in the inhibition of splicing at 3'-splice site A3.
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