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Title: Molecular study of SRF-cofactor interactions
Author: Zaromytidou, Alexia Ileana
ISNI:       0000 0001 3576 8560
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2008
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Serum Response Factor regulates a large array of genes involved in diverse processes including cell proliferation, muscle differentiation and development, and cytoskeletal processes such as cell migration and adhesion. The specificity and versatility of the SRF responses is achieved by combinatorial interactions with accessory factors. SRF binds to the CC(A/T)2A(A/T)3GG CArG box consensus sequence within the promoters of its target genes and acts as a docking platform for diverse signal regulated and cell- type specific cofactors to elicit their distinct responses. In fibroblasts two pathways signal through SRF in a mutually exclusive manner. MAP kinase signalling results in transcriptional activation of a subset of SRF target genes, via the interaction of SRF with members of the TCF family of Ets domain proteins. In contrast Rho-signalling induced changes in actin dynamics result in the association of SRF with members of the Myocardin-related family of SRF cofactors (MAL/MRTF-A/MKL1 and MAL16/MRTF-B/MKL2). The results described in this thesis characterise the molecular mechanism of MAL-SRF complex formation. MAL binds SRF as a dimer via a seven-residue core sequence within the MAL B1 region. Residues in the neighbouring Q-box enhance MAL-SRF complex formation, although these do not contact SRF directly. The MAL-SRF interaction displays the properties of a Rho-regulated cofactor. MAL competes with TCF for SRF binding due to the interaction of both cofactors with the same hydrophobic groove and pocket on SRF. In contrast to TCF, MAL-SRF complex formation depends on the intact N-terminus of the SRF DNA-binding domain. Mutations in the SRF al-helix that reduce DNA bending also impair complex formation with MAL. These mutations however do not affect DNA distortion in the MAL-SRF complex. Efficient MAL-SRF complex formation requires that SRF be bound to its cognate DNA and that MAL directly contacts DNA on either side of the CArG box. My results support a model in which each MAL monomer adds a p-strand consisting of the core B1 sequence, to the p-sheet of the SRF DNA-binding domain in a similar way to TCF, while also making direct DNA contacts in the ternary complex facilitated by SRF- induced DNA distortion. My analysis of complex formation between MAL and SRF demonstrates that members of the MRTF and TCF families of SRF cofactors interact with SRF using related but distinct mechanisms, thus providing a molecular rationale for their mutually exclusive transcriptional responses and the specificity of signalling to SRF.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available