title: HEXIM1 targets a repeated GAUC motif in the riboregulator of transcription 7SK and promotes base pair rearrangements.
abstract: 7SK snRNA, an abundant RNA discovered in human nucleus, regulates transcription by RNA polymerase II (RNAPII). It sequesters and inhibits the transcription elongation factor P-TEFb which, by phosphorylation of RNAPII, switches transcription from initiation to processive elongation and relieves pauses of transcription. This regulation process depends on the association between 7SK and a HEXIM protein, neither isolated partner being able to inhibit P-TEFb alone. In this work, we used a combined NMR and biochemical approach to determine 7SK and HEXIM1 elements that define their binding properties. Our results demonstrate that a repeated GAUC motif located in the upper part of a hairpin on the 5'-end of 7SK is essential for specific HEXIM1 recognition. Binding of a peptide comprising the HEXIM Arginine Rich Motif (ARM) induces an opening of the GAUC motif and stabilization of an internal loop. A conserved proline-serine sequence in the middle of the ARM is shown to be essential for the binding specificity and the conformational change of the RNA. This work provides evidences for a recognition mechanism involving a first event of induced fit, suggesting that 7SK plasticity is involved in the transcription regulation.
authors.affiliation: IGBMC, BP10142, 1 rue Laurent Fries, 67404 Illkirch Cedex, France. lebars@igbmc.fr
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lebars
authors.forename: D
authors.initials: D
authors.lastname: Martinez-Zapien
authors.forename: A
authors.initials: A
authors.lastname: Durand
authors.forename: J
authors.initials: J
authors.lastname: Coutant
authors.forename: B
authors.initials: B
authors.lastname: Kieffer
authors.forename: Anne-Catherine
authors.initials: AC
authors.lastname: Dock-Bregeon
mesh_terms: D020029:Base Pairing; D001483:Base Sequence; D001665:Binding Sites; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012342:RNA, Small Nuclear / Q000737:chemistry* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D014157:Transcription Factors
chemical_list: C476123:HEXIM1 protein, human; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D014157:Transcription Factors