Tat-SF1 is not required for Tat transactivation but does regulate the relative levels of unspliced and spliced HIV-1 RNAs

Heather B. Miller, Kevin O. Saunders, Georgia D. Tomaras, Mariano Garcia-Blanco

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Abstract

Background: HIV-1 relies on several host proteins for productive viral transcription. HIV-1 Tat-specific factor 1 (Tat-SF1) is among these cofactors that were identified by in vitro reconstituted transcription reactions with immunodepleted nuclear extracts. At the onset of this work, the prevailing hypothesis was that Tat-SF1 was a required cofactor for the viral regulatory protein, Tat; however, this had not previously been formally tested in vivo. Methodology/Principal Findings: To directly address the involvement of Tat-SF1 in HIV-1 gene expression, we depleted Tat-SF1 in HeLa cells by conventional expression of shRNAs and in T- Rex -293 cells containing tetracycline-inducible shRNAs targeting Tat-SF1. We achieved efficient depletion of Tat-SF1 and demonstrated that this did not affect cell viability. HIV-1 infectivity decreased in Tat-SF1-depleted cells, but only when multiple rounds of infection occurred. Neither Tat-dependent nor basal transcription from the HIV-1 LTR was affected by Tat-SF1 depletion, suggesting that the decrease in infectivity was due to a deficiency at a later step in the viral lifecycle. Finally, Tat-SF1 depletion resulted in an increase in the ratio of unspliced to spliced viral transcripts. Conclusions/Significance: Tat-SF1 is not required for regulating HIV-1 transcription, but is required for maintaining the ratios of different classes of HIV-1 transcripts. These new findings highlight a novel, post-transcriptional role for Tat-SF1 in the HIV-1 life cycle.

Original languageEnglish (US)
Article numbere5710
JournalPLoS One
Volume4
Issue number5
DOIs
StatePublished - May 27 2009
Externally publishedYes

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ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

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