Regulation of polymerase II transcription by 7SK snRNA: two distinct RNA elements direct P-TEFb and HEXIM1 binding.
The positive transcription elongation factor b (P-TEFb), a complex of Cdk9 and cyclin T1/T2, stimulates transcription by phosphorylating RNA polymerase II. The 7SK small nuclear RNA, in cooperation with HEXIM1 protein, functions as a general polymerase II transcription regulator by sequestering P-TEFb into a large kinase-inactive 7SK/HEXIM1/P-TEFb complex. Here, determination and characterization of the functionally essential elements of human 7SK snRNA directing HEXIM1 and P-TEFb binding led to a new model for the assembly of the 7SK/HEXIM1/P-TEFb regulatory complex. We demonstrate that two structurally and functionally distinct protein binding elements located in the 5'- and 3'-terminal hairpins of 7SK support the in vivo recruitment of HEXIM1 and P-TEFb. Consistently, a minimal regulatory RNA composed of the 5' and 3' hairpins of 7SK can modulate polymerase II transcription in HeLa cells. HEXIM1 binds independently and specifically to the G24-C48/G60-C87 distal segment of the 5' hairpin of 7SK. Binding of HEXIM1 is a prerequisite for association of P-TEFb with the G302-C324 apical region of the 3' hairpin of 7SK that is highly reminiscent of the human immunodeficiency virus transactivation-responsive RNA.
Egloff
Sylvain
S
Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099 and Université Paul Sabatier, IFR109, 118 route de Narbonne, 31062 Toulouse Cedex 4, France.
Van Herreweghe
Elodie
E
Kiss
Tamás
T
D024509:3' Flanking Region; D024506:5' Flanking Region; D001483:Base Sequence; D002460:Cell Line; D017124:Conserved Sequence; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010766:Phosphorylation; D042925:Positive Transcriptional Elongation Factor B / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D015533:Transcriptional Activation
C476123:HEXIM1 protein, human; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D042925:Positive Transcriptional Elongation Factor B; D012319:RNA Polymerase II