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RNA-mediated displacement of an inhibitory snRNP complex activates transcription elongation

Nature Structural & Molecular Biology volume 17, pages 815–821 (2010)Cite this article

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Abstract

The transition from transcription initiation to elongation at the HIV-1 promoter is controlled by Tat, which recruits P-TEFb to TAR RNA to phosphorylate RNA polymerase II. It has long been unclear why the HIV-1 promoter is incompetent for elongation. We report that P-TEFb is recruited to the promoter in a catalytically inactive state bound to the inhibitory 7SK small nuclear ribonucleoprotein (snRNP), thereby preventing elongation. It also has long been believed that TAR functions to recruit Tat to the promoter, but we find that Tat is recruited to the DNA template before TAR is synthesized. We propose that TAR binds Tat and P-TEFb as it emerges on the nascent transcript, competitively displacing the inhibitory 7SK snRNP and activating the P-TEFb kinase. Recruitment of an inhibitory snRNP complex at an early stage in the transcription cycle provides a new paradigm for controlling gene expression with a noncoding RNA.

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Figure 1: Inactive P-TEFb assembles into Pol II complexes, and Tat activates its catalytic activity.
Figure 2: Distribution of Tat and cofactors at the HIV-1 promoter and dependence on TAR.
Figure 3: Tat assembles with the 7SK snRNP in vivo.
Figure 4: 7SK snRNP and Tat recruitment to HIV-1 PICs are Sp1 dependent.
Figure 5: Proposed model of HIV-1 transcription activation by Tat.

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Acknowledgements

We thank K. Yamamoto, P. Walter, C. Guthrie, R. Andino, J. Gross and N. Krogan for comments, J. Greenblatt (Univ. of Toronto) for reagents, members of the Frankel and Yamamoto laboratory for discussions and the reviewers for their insightful comments. This work was initially supported by an amfAR Mathilde Krim fellowship in Basic Biomedical Research (106988-43-RFNT) and a US National Institutes of Health K99/R00 grant A112185 to I.D. as well as US National Institutes of Health grants AI29135 and P50 GM082250 (HARC Center) to A.D.F.

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  1. Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA

    Iván D'Orso & Alan D Frankel

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  1. Iván D'Orso
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  2. Alan D Frankel
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I.D. and A.D.F. designed research; I.D. performed research; I.D. and A.D.F. analyzed data and wrote the paper

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Correspondence to Alan D Frankel.

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D'Orso, I., Frankel, A. RNA-mediated displacement of an inhibitory snRNP complex activates transcription elongation. Nat Struct Mol Biol 17, 815–821 (2010). https://doi.org/10.1038/nsmb.1827

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