7SK RNA

In molecular biology 7SK is an abundant small nuclear RNA found in metazoans.[1] It plays a role in regulating transcription by controlling the positive transcription elongation factor P-TEFb.[2] 7SK is found in a small nuclear ribonucleoprotein complex (snRNP) with a number of other proteins that regulate the stability and function of the complex.

Reversible association of P-TEFb with the 7SK snRNP. P-TEFb is released from the 7SK snRNP by Brd4 or HIV Tat. HEXIM is ejected and the two proteins are replaced by hrRNPs. The reverse of this process requires other unknown factors.
7SK RNA
Predicted secondary structure and sequence conservation of 7SK
Identifiers
Symbol7SK
RfamRF00100
Other data
RNA typeGene
Domain(s)Eukaryota
SOSO:0000274
PDB structuresPDBe
RN7SK
Identifiers
SymbolRN7SK
NCBI gene125050
Other data
LocusChr. 6 p12.2

Structure

An early study indicated that 7SK in cells is associated with a number of proteins and probing of the secondary structure suggested a model for base pairing between different regions of the RNA.[3] A breakthrough in the function of the 7SK snRNP came with the finding that the positive transcription elongation factor P-TEFb was a component of the complex.[4][5] 7SK associates with and inhibits the cyclin dependent kinase activity of P-TEFb through the action of the RNA binding proteins HEXIM1[6][7] or HEXIM2.[8][9] The gamma phosphate at the 5' end of 7SK is methylated by the methylphosphate capping enzyme MEPCE which is a constitutive component of the 7SK snRNP.[10] A La related protein LARP7 is also found associated with 7SK, presumably in part through its interaction with the 3' end of the RNA.[11][12][13] Reduction of either MEPCE or LARP7 by siRNA mediated knockdown leads to destabilization of 7SK in vivo. A subset of 7SK snRNPs lack P-TEFb and HEXIM, but contains hnRNPs instead.[14]

Function

The major function of the 7SK snRNP is control of the P-TEFb, a factor that regulates the elongation phase of transcription.[2] The kinase activity of P-TEFb is inhibited when the factor is in the 7SK snRNP. P-TEFb can be released from the 7SK snRNP by either the HIV transactivator Tat or the bromodomain containing protein BRD4. This release leads to a conformational change in 7SK RNA and the ejection of HEXIM.[15] hnRNPs stabilize the complex lacking P-TEFb and HEXIM. After P-TEFb functions on specific genes it is re-sequestered in the 7SK snRNP by an unknown mechanism. The 7SK snRNP has been characterized in both human and Drosophila.[16] Detailed review.[14]

References
  1. Diribarne G, Bensaude O (2009). "7SK RNA, a non-coding RNA regulating P-TEFb, a general transcription factor". RNA Biology. 6 (2): 122–8. doi:10.4161/rna.6.2.8115. PMID 19246988.
  2. Peterlin BM, Brogie JE, Price DH (2012). "7SK snRNA: a noncoding RNA that plays a major role in regulating eukaryotic transcription". Wiley Interdisciplinary Reviews. RNA. 3 (1): 92–103. doi:10.1002/wrna.106. PMC 3223291. PMID 21853533.
  3. Wassarman DA, Steitz JA (July 1991). "Structural analyses of the 7SK ribonucleoprotein (RNP), the most abundant human small RNP of unknown function". Molecular and Cellular Biology. 11 (7): 3432–45. doi:10.1128/MCB.11.7.3432. PMC 361072. PMID 1646389.
  4. Nguyen VT, Kiss T, Michels AA, Bensaude O (November 2001). "7SK small nuclear RNA binds to and inhibits the activity of CDK9/cyclin T complexes". Nature. 414 (6861): 322–5. Bibcode:2001Natur.414..322N. doi:10.1038/35104581. PMID 11713533. S2CID 4341651.
  5. Yang Z, Zhu Q, Luo K, Zhou Q (November 2001). "The 7SK small nuclear RNA inhibits the CDK9/cyclin T1 kinase to control transcription". Nature. 414 (6861): 317–22. Bibcode:2001Natur.414..317Y. doi:10.1038/35104575. PMID 11713532. S2CID 4379065.
  6. Michels AA, Nguyen VT, Fraldi A, Labas V, Edwards M, Bonnet F, et al. (July 2003). "MAQ1 and 7SK RNA interact with CDK9/cyclin T complexes in a transcription-dependent manner". Molecular and Cellular Biology. 23 (14): 4859–69. doi:10.1128/MCB.23.14.4859-4869.2003. PMC 162212. PMID 12832472.
  7. Yik JH, Chen R, Nishimura R, Jennings JL, Link AJ, Zhou Q (October 2003). "Inhibition of P-TEFb (CDK9/Cyclin T) kinase and RNA polymerase II transcription by the coordinated actions of HEXIM1 and 7SK snRNA". Molecular Cell. 12 (4): 971–82. doi:10.1016/S1097-2765(03)00388-5. PMID 14580347.
  8. Byers SA, Price JP, Cooper JJ, Li Q, Price DH (April 2005). "HEXIM2, a HEXIM1-related protein, regulates positive transcription elongation factor b through association with 7SK". The Journal of Biological Chemistry. 280 (16): 16360–7. doi:10.1074/jbc.M500424200. PMID 15713662.
  9. Yik JH, Chen R, Pezda AC, Zhou Q (April 2005). "Compensatory contributions of HEXIM1 and HEXIM2 in maintaining the balance of active and inactive positive transcription elongation factor b complexes for control of transcription". The Journal of Biological Chemistry. 280 (16): 16368–76. doi:10.1074/jbc.M500912200. PMID 15713661.
  10. Jeronimo C, Forget D, Bouchard A, Li Q, Chua G, Poitras C, et al. (July 2007). "Systematic analysis of the protein interaction network for the human transcription machinery reveals the identity of the 7SK capping enzyme". Molecular Cell. 27 (2): 262–74. doi:10.1016/j.molcel.2007.06.027. PMC 4498903. PMID 17643375.
  11. Krueger BJ, Jeronimo C, Roy BB, Bouchard A, Barrandon C, Byers SA, et al. (April 2008). "LARP7 is a stable component of the 7SK snRNP while P-TEFb, HEXIM1 and hnRNP A1 are reversibly associated". Nucleic Acids Research. 36 (7): 2219–29. doi:10.1093/nar/gkn061. PMC 2367717. PMID 18281698.
  12. Markert A, Grimm M, Martinez J, Wiesner J, Meyerhans A, Meyuhas O, et al. (June 2008). "The La-related protein LARP7 is a component of the 7SK ribonucleoprotein and affects transcription of cellular and viral polymerase II genes". EMBO Reports. 9 (6): 569–75. doi:10.1038/embor.2008.72. PMC 2427381. PMID 18483487.
  13. He N, Jahchan NS, Hong E, Li Q, Bayfield MA, Maraia RJ, et al. (March 2008). "A La-related protein modulates 7SK snRNP integrity to suppress P-TEFb-dependent transcriptional elongation and tumorigenesis". Molecular Cell. 29 (5): 588–99. doi:10.1016/j.molcel.2008.01.003. PMC 6239424. PMID 18249148.
  14. C Quaresma AJ, Bugai A, Barboric M (September 2016). "Cracking the control of RNA polymerase II elongation by 7SK snRNP and P-TEFb". Nucleic Acids Research. 44 (16): 7527–39. doi:10.1093/nar/gkw585. PMC 5027500. PMID 27369380.
  15. Krueger BJ, Varzavand K, Cooper JJ, Price DH (August 2010). Blagosklonny MV (ed.). "The mechanism of release of P-TEFb and HEXIM1 from the 7SK snRNP by viral and cellular activators includes a conformational change in 7SK". PLOS ONE. 5 (8): e12335. Bibcode:2010PLoSO...512335K. doi:10.1371/journal.pone.0012335. PMC 2925947. PMID 20808803.
  16. Nguyen D, Krueger BJ, Sedore SC, Brogie JE, Rogers JT, Rajendra TK, et al. (July 2012). "The Drosophila 7SK snRNP and the essential role of dHEXIM in development". Nucleic Acids Research. 40 (12): 5283–97. doi:10.1093/nar/gks191. PMC 3384314. PMID 22379134.
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