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Home > Departments > Genome Biology > Julie SOUTOURINA : Genome transcriptional regulation

Julie SOUTOURINA : Group Presentation

The group is interested in molecular mechanisms of eukaryotic transcriptional regulation in vivo on the genomic scale. We use the budding yeast Saccharomyces cerevisiae and human cells and apply integrative approaches to understand how the transcriptional regulation works and how transcription is coordinated with others nuclear processes like DNA repair.

Research subjects

1 – Genome-wide mechanisms of transcriptional regulation in eukaryotes

In eukaryotes, transcription as a first step of gene expression is tightly regulated and many multiprotein complexes are implicated in this essential process. Mediator of transcription regulation is one of these complexes essential during the activation of RNA polymerase II. This coactivator is responsible for the recruitment of RNA polymerase II to promoters in response to transcription activators. Mediator is a large multi-protein complex (1.5MDa) composed of 25 - 30 subunits and conserved in all eukaryotes. As expected given its central role in transcription activation, mutations in its subunits are involved in pathologies like cancers. The crucial role of Mediator in transcription activation is now largely accepted. However, the complexity of this complex has precluded a detailed understanding of the mechanisms of its action that is one of the keys for understanding gene expression regulation. Previously, using the two-hybrid approach we proposed a model of the organization of the complex (Guglielmi et al. 2004). Many interactions that we uncovered were confirmed by crystallographic studies.
The general transcription factor TFIIS, that plays an important role in transcription elongation, cooperates with Mediator in the activation of a subset of the yeast genome (Guglielmi et al. 2007). We demonstrated that TFIIS plays also an important role in RNA polymerase III transcription, stimulating the transcription of this class of genes (Ghavi-Helm et al. 2008). We further extended this work on the genome of mouse embryonic stem cells and found that TFIIS function in RNA polymerase III transcription is conserved in mammals (Carrière et al. 2012). These findings have led to reconsider and to extend largely the role of TFIIS transcription factor in genome expression.
We are now interested in the role of Mediator in transcription activation and, in particular, in preinitiation complex formation. Using the yeast Saccharomyces cerevisiae as our main model and integrative biology approaches, we have established the role of Mediator in the recruitment of Pol II and a general transcription factor TFIIH, contributing to our understanding of Mediator function. Our study has led to the discovery of an essential role of Mediator in TFIIH general transcription factor recruitment and allows us to propose a new model in preinitiation complex formation during transcription activation (Esnault et al. 2008). We identified one subunit in Mediator and one in RNA polymerase II that directly contact each other. We showed that this contact is required for transcription of all genes in yeast, dissecting an essential mechanism for the expression of genomes in eukaryotes (Soutourina et al. 2011).
Currently, we are investigating the role of the 10 essential subunits of Mediator in stimulating the assembly of preinitiation complexes genome-wide using genetic, biochemical and functional genomics approaches. We are trying to uncover the rules that determine the pathways of assembly of preinitiation complexes in vivo.

Figure 1: The first step of transcription activation consists in the recruitment of the Mediator complex by transcription activation. The complex can then recruit RNA polymerase II or TFIIE and cTFIIH general transcription factors. These intermediates can lead to the formation of a full preinitiation complex through various “branched” pathways.

2 – Mediator functions beyond transcription

Transcription is coupled with DNA repair, ensuring the continuity of Pol II progression. DNA lesions can potentially lead to problems in development, cell growth and survival. Proteins first identified as components of transcription or DNA repair machineries may be involved in both processes, like TFIIH. Nucleotide-excision DNA repair (NER) is a major DNA repair pathway that removes DNA lesions such as cyclobutane pyrimidine dimers (CPD) arising upon UV irradiation. Global genome repair pathway removes DNA lesions in the genome overall, and transcription-coupled repair removes DNA lesions that interfere with the progression of Pol II through actively-transcribed genes. While the NER reaction and the components required for efficient DNA lesion recognition and repair are fairly well understood in vitro, many questions on the active coupling of DNA repair with transcription remain still unanswered in vivo, notably on the genomic scale.
Our two-hybrid screening with Mediator subunits (Guglielmi et al. 2004) permits us to uncover a number of interactions between Mediator and other components of the nucleus (unpublished data). One particularly interesting interaction that we have identified is the contact between one of the Mediator subunits and a DNA repair protein. We uncovered a new role of Mediator by connecting transcription and DNA repair via this direct contact with Rad2 endonuclease, the yeast homolog of human XPG protein (Eyboulet et al. 2013). Mutations in human XPG gene give rise to a xeroderma pigmentosum (XP) associated with Cockayne syndrome (CS) disease. Our results indicated that Mediator is involved in transcription-coupled DNA repair by facilitating Rad2 recruitment to transcribed genes. We propose that in addition to its fundamental coactivator role, Mediator acts in essential nuclear processes beyond transcription (Eyboulet et al. 2014; Soutourina & Werner 2014).

©CEA/J. Soutourina

Figure 2: Coactivator function of Mediator in Pol II transcription and a new role of this complex in transcription-coupled DNA repair via a direct contact with Rad2/XPG.

Key words :

Budding yeast Saccharomyces cerevisiae; Mammalian cells; Transcription regulation; Transcription-coupled repair; RNA polymerase; Mediator; Rad2/XPG; TFIIS; xeroderma pigmentosum/Cockayne syndrome; Functional genomics

Contact :

SOUTOURINA Julie [Researcher - CEA]
Department of genomes biology [Deputy]
Genome transcriptional regulation [Leader]
01 69 08 54 13 Saclay - Bât 144

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