RNA Polymerase II Elongation
The Price Lab is interested in all processes that take place during the elongation phase of transcription by RNA polymerase II. This includes the elongation control process which is mediated by P-TEFb, termination by TTF2, and the RNA processing events that are functionally coupled to transcription elongation. We are also involved in understanding how HIV-1 utilizes the elongation control system during active infections and latency.
Function of P-TEFb
The positive transcription elongation factor, P-TEFb, is a cyclin dependent kinase that regulates the production of mRNAs by relieving a constitutive block to elongation that occurs at the 5' end of genes shortly after initiation of transcription. Five factors have been identified that contribute to promoter proximal pausing, DSIF and NELF, TFIIS, Gdown1 and the Gdown1 negative accessory factor, GNAF. The P-TEFb mediated transition into productive elongation involves phosphorylation of DSIF, NELF and the CTD of RNA polymerase II. We are currently examining the details of promoter proximal pausing and the mechanism of the transition into productive elongation. Our approach is to use in vitro transcription, as well as ChIP-Seq and other biochemical and molecular tools, to obtain details of the mechanisms involved.
Control of P-TEFb
P-TEFb is regulated by reversible interaction with the 7SK snRNP. Association with HEXIM1 or HEXIM2 in the 7SK snRNP inhibits P-TEFb and maintains a large store of P-TEFb that can be released when and potentially where it is needed. LARP7 and MePCE are constitutive components of the 7SK snRNP that maintain stability of the complex and are likely involved in the regulated release of P-TEFb. Studies are underway to uncover the mechanisms that control release and re-sequestration of P-TEFb into the 7SK snRNP.
Function of TTF2
The transcription termination factor TTF2 is an ATP driven motor that travels on dsDNA and causes RNA polymerase II to terminate. One of its major roles is to repress transcription during mitosis. Current studies are aimed at determining if it plays a role in normal 3' end formation during interphase and if is needed for transcription coupled repair.
Regulation of HIV-1 Transcription
Once the HIV genome is integrated into the host genome it is transcribed by RNA polymerase II and expression of viral genes is controlled by P- TEFb. HIV takes control of the P-TEFb control process through the use of a small viral protein, Tat, that takes P- TEFb from the 7SK snRNP and delivers it to the TAR element in the 5' end of the nascent HIV transcript. In collaboration with the Tahirov lab (UNMC) we recently solved the structure of an HIV Tat - P-TEFb complex. This structure should be useful in developing anti-HIV treatments that do not target the uncomplexed P-TEFb.