The multiprotein Mediator complex (MED) is a key element of the general transcriptional machinery which acts as a dynamic interface between specific transcription factors (STFs) and the RNA polymerase II enzyme (RD Kornberg, TIBS, 2005). Through bioinformatics analyses we have shown that most MED subunits have been conserved from unicellular organisms to man (Boube et al, Cell, 2002; Bourbon et al, Mol Cell, 2005; Bourbon, Nucleic Acids Res, 2008).
We are studying MED function in vivo by using the Drosophila model. Genetic analyses have shown that the Med12 and Med13 subunits are specifically required for regionalized expression of the bric-à-brac2 gene (bab2), a developmental gene required for distal leg differentiation (Loncle et al, EMBO J, 2007). In collaboration with J.L. Couderc (Clermont-Ferrand, France), we have identified two regulatory DNA elements which (1) drive bab2 expression in larval tissues at the origin of adult legs, (2) require Med12-13 activity and (3) include potential binding sites for various STFs required for regionalized bab2 expression.
The project includes two parts: (1) Identification of STFs directly participating to the regulation of bab2 expression, through characterization of binding sites in vitro and in vivo. (2) Detailed analyses of functional links between bab2 regulatory STFs and the MED complex, particularly Med12-13. To this end, we will perform genetic epistasis tests between Med12-13 and each of the previously-identified STFs, as well as an analysis of physical interactions between MED and the same STFs, in vitro and in vivo (including chromatin immunoprecipitation assays from larval extracts prepared from wild-type or mutant animals).
This project will allow us to better understand how MED integrates combinatorial regulatory information from STFs to fine-tune transcription in vivo.
Funding Notes
3 years-funded PhD starting October 2008 in Toulouse, France
Funded by CNRS and Midi-Pyrénées
Salary : 1757 euros per month, including taxes
Candidates should have a master degree since less than 2 years
References from the team on the research subject:
(1) Boube, M., C. Faucher, L. Joulia, D. L. Cribbs and H.-M. Bourbon (2000). Drosophila homologs of transcriptional mediator complex subunits are required for adult cell and segment identity specification. Genes Dev 14: 2906-2917.
(2) Boube, M., L. Joulia, D.L. Cribbs and H.-M. Bourbon (2002). Evidence for a Mediator of RNA polymerase II transcriptional regulation conserved from yeast to man. Cell 110: 143-151.
(3) Bourbon, H.-M., et al. (2004). A unified nomenclature for protein subunits of mediator complexes linking transcriptional regulators to RNA polymerase II. Mol Cell 14, 553-7.
(4) Guglielmi, B., van Berken, N., Klapholz, B., Bijma, T., Boube, M., Boschiero, C., Bourbon, H.-M., Holstege, F.C.P., and Werner, M. (2004). A high resolution protein interaction map of the yeast Mediator complex. Nucleic Acids Res 32, 5379-91.
(5) Loncle, N., Boube, M., Joulia, L., Boschiero, C., Werner, M., Cribbs, D.L., and Bourbon, H.M. (2007). Distinct roles for Mediator Cdk8 module subunits in Drosophila development. EMBO J, 26, 1045-1054.
(6) Bourbon, H.M. (2008). Comparative genomics supports a deep evolutionary origin for the large, four-module transcriptional Mediator complex. Nucleic Acids Res, in the press.
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