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Title: An investigation into the structural role of the CCR4-NOT complex in mRNA stability
Author: Brazier, Hannah
ISNI:       0000 0004 7229 9291
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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The CCR4-NOT complex is a global regulator of gene expression which controls mRNA levels by removing the poly-(A) tail, a step known as deadenylation and one that constitutes the rate-limiting step in mRNA decay. The human complex is comprised of eight stably associated CNOT subunits where CNOT1 forms the scaffold onto which CNOT2-11 bind. Although much has been learnt about the CCR4-NOT complex, questions still remain. Thus, this study focused on a number of sub-complexes of CNOT subunits and associated proteins to determine the mode of interaction with a hope to explore the mechanism of deadenylation by the CCR4-NOT complex. Firstly, the complex of CNOT10:CNOT11, found only in higher eukaryotes, was reconstituted for the first time using recombinant proteins. Crystallisation trials, limited proteolysis and mass spectrometry were used to isolate novel interaction regions between CNOT10 and CNOT11 which may provide direction for future structural and functional studies. Secondly, the interaction between CNOT9 and TTP was characterised. TTP is a RNA-binding protein which targets inflammatory mRNAs for deadenylation by recruiting the CCR4-NOT complex. This study highlights novel interactions between TTP and both CNOT2 and CNOT9. Moreover, BioLayer interferometry (BLI), peptide arrays and site-directed mutagenesis identified that TTP interacts with CNOT9 in a tryptophan-mediated manner. These findings change the known interface between TTP and the CCR4-NOT complex. Lastly, the MultiBac system was used to reconstitute a number of human CNOT sub-complexes, one of which was shown to effectively degrade a poly-(A) substrate, demonstrating it is enzymatically active. This achievement provides a tool for the future study of the CCR4-NOT complex. In summary, this study highlights novel interactions and characterises previously unknown binding mechanisms between CCR4-NOT subunits which expands our current understanding of the complex.
Supervisor: Yue, Wyatt ; Burgess-Brown, Nicola ; Dean, Jonathan Sponsor: Kennedy Institute of Rheumatology
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Protein expression ; Expression of protein complexes ; Deadenylation ; Inflammatory gene expression