title: Oligomerization of HEXIM1 via 7SK snRNA and coiled-coil region directs the inhibition of P-TEFb.
abstract: Transcriptional elongation of most eukaryotic genes by RNA polymerase II requires the kinase activity of the positive transcription elongation factor b (P-TEFb). The catalytically active P-TEFb complex becomes inactive when sequestered into the large complex by the cooperative actions of 7SK snRNA and HEXIM1. In this study, we report that HEXIM1 forms oligomers in cells. This oligomerization is mediated by its predicted coiled-coil region in the C-terminal domain and 7SK snRNA that binds a basic region within the central part of HEXIM1. Alanine-mutagenesis of evolutionary conserved leucines in the coiled-coil region and the digestion of 7SK snRNA by RNase A treatment prevent this oligomerization. Importantly, mutations of the N-terminal part of the coiled-coil region abrogate the ability of HEXIM1 to bind and inhibit P-TEFb. Finally, the formation of HEXIM1 oligomers via the C-terminal part of the coiled-coil or basic regions is critical for the inhibition of transcription. Our results suggest that two independent regions in HEXIM1 form oligomers to incorporate P-TEFb into the large complex and determine the inhibition of transcriptional elongation.
authors.affiliation: Department of Medicine, Rosalind Russell Medical Research Center, University of California at San Francisco, San Francisco, CA 94143-0703, USA.
authors.forename: Dalibor
authors.initials: D
authors.lastname: Blazek
authors.forename: Matjaz
authors.initials: M
authors.lastname: Barboric
authors.forename: Jiri
authors.initials: J
authors.lastname: Kohoutek
authors.forename: Irena
authors.initials: I
authors.lastname: Oven
authors.forename: B Matija
authors.initials: BM
authors.lastname: Peterlin
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D019143:Evolution, Molecular; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D042925:Positive Transcriptional Elongation Factor B / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012342:RNA, Small Nuclear / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: C476123:HEXIM1 protein, human; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D042925:Positive Transcriptional Elongation Factor B