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The 3′UTR of HIC mRNA activates transcription via P‐TEFb
Author(s) -
Mathews Michael B,
Young Tara M,
Pe’ery Tsafi
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a540-c
Subject(s) - p tefb , microbiology and biotechnology , three prime untranslated region , untranslated region , rna polymerase ii , biology , transcription (linguistics) , five prime untranslated region , messenger rna , promoter , gene expression , genetics , gene , linguistics , philosophy
P‐TEFb (positive transcription elongation factor b) is a general transcription factor and an essential cofactor for HIV‐1 transcription. It contains a CTD kinase, CDK9, and its cyclin partner, cyclin T1. In cells, a fraction of P‐TEFb is present in a repressed form associated with the 7SK small nuclear RNA and HEXIM protein. We previously isolated HIC (human I‐mfa containing protein) as a P‐TEFb interacting protein by using the yeast two‐hybrid system. The HIC protein binds to cyclin T1, and transfection of HIC cDNA increases Tat‐dependent expression from the HIV‐1 promoter. Unexpectedly, this transcriptional stimulation is predominantly due to the long 3′ untranslated region (3′UTR) of HIC mRNA rather than its open reading frame. Transfection experiments were performed using the dual luciferase assay and portions of the HIC cDNA. We found that the 3′UTR is necessary and sufficient for stimulation of expression from the HIV‐1 promoter and other promoters. The shortest 3′UTR fragment with full activity was 313bp long. We hypothesized that the 3′UTR of HIC displaces 7SK from P‐TEFb complexes. Consistent with this idea, the 3′UTR of endogenous HIC mRNA is associated with P‐TEFb. Transfected HIC 3′UTR binds to P‐TEFb and displaces 7SK RNA from the inhibitory complex but the 3′UTRs of control genes were inactive. HIC 3′UTR, but not control 3′UTR, released 7SK from P‐TEFb in vitro. Furthermore, HEXIM1 overexpression antagonized P‐TEFb activation by HIC 3′UTR. These data show that P‐TEFb dependent transcription can be regulated by mRNA sequences via release of 7SK, and suggest a novel function for the 3′UTR in transcriptional control. (Supported by grants from NIH‐NIAID to MBM and TP).