HEXIM is a transcriptional regulator that functions as a general RNA polymerase II transcription inhibitor. In cooperation with 7SK snRNA it sequesters P-TEFb in a large inactive 7SK snRNP complex preventing RNA polymerase II phosphorylation and subsequent transcriptional elongation. HEXIM may also regulate NF-kappa-B, ESR1, NR3C1 and CIITA-dependent transcriptional activity.

1: Suppression of NF-kappaB-dependent gene expression by a hexamethylene bisacetamide-inducible protein HEXIM1 in human vascular smooth muscle cells. Ouchida R, Kusuhara M, Shimizu N, Hisada T, Makino Y, Morimoto C, Handa H, Ohsuzu F, Tanaka H; Genes Cells. 2003;8:95-107. PMID:12581153

2: Inhibition of P-TEFb (CDK9/Cyclin T) kinase and RNA polymerase II transcription by the coordinated actions of HEXIM1 and 7SK snRNA. Yik JH, Chen R, Nishimura R, Jennings JL, Link AJ, Zhou Q; Mol Cell. 2003;12:971-982. PMID:14580347

3: Structure of the Cyclin T binding domain of Hexim1 and molecular basis for its recognition of P-TEFb. Dames SA, Schonichen A, Schulte A, Barboric M, Peterlin BM, Grzesiek S, Geyer M; Proc Natl Acad Sci U S A. 2007;104:14312-14317. PMID:17724342