title: HEXIM2, a HEXIM1-related protein, regulates positive transcription elongation factor b through association with 7SK.
abstract: The kinase activity of positive transcription elongation factor b (P-TEFb), composed of cyclin-dependent kinase 9 and cyclin T1 or T2, is required for the transition of RNA polymerase II into productive elongation. P-TEFb activity has been shown to be negatively regulated by association with the small nuclear RNA 7SK and the HEXIM1 protein. Here, we characterize HEXIM2, a previously predicted protein with sequence similarity to HEXIM1. HEXIM2 is expressed in HeLa and Jurkat cells, and glycerol gradient analysis and immunoprecipitations indicate that HEXIM2, like HEXIM1, has a regulated association with P-TEFb. As HEXIM1 is knocked down, HEXIM2 functionally compensates for its association with P-TEFb. Electrophoretic mobility shift assays and in vitro kinase assays demonstrate that HEXIM2 forms complexes containing 7SK and P-TEFb and, in conjunction with 7SK, inhibits P-TEFb kinase activity. Our results provide strong evidence that HEXIM2 is a regulator of P-TEFb function. Furthermore, our results support the idea that the utilization of HEXIM1 or HEXIM2 to bind and inhibit P-TEFb can be differentially regulated in vivo.
authors.affiliation: Molecular Biology Program and Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Byers
authors.forename: Jason P
authors.initials: JP
authors.lastname: Price
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Cooper
authors.forename: Qintong
authors.initials: Q
authors.lastname: Li
authors.forename: David H
authors.initials: DH
authors.lastname: Price
mesh_terms: D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D042925:Positive Transcriptional Elongation Factor B / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D012342:RNA, Small Nuclear / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D014157:Transcription Factors
chemical_list: C476123:HEXIM1 protein, human; C501428:HEXIM2 protein, human; D034741:RNA, Small Interfering; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D014157:Transcription Factors; D042925:Positive Transcriptional Elongation Factor B