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Title: The mechanism of mariner transposition : a molecular analysis of the human Hsmar1 transposon
Author: Claeys Bouuaert, Corentin
ISNI:       0000 0004 2721 0630
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2011
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Transposons are specialized genetic elements that mobilize and amplify within a host genome. They are disruptive by nature and are therefore considered as molecular parasites, but they are also important evolutionary forces. The Tc1-mariner superfamily of transposons is particularly widespread in eukaryotes. These elements transpose via a cut-and-paste mechanism and are unusual in that double-strand cleavage of the transposon ends does not rely on the formation of a hairpin intermediate. This suggests that Tc1-mariner elements use a fundamentally different mechanism of transposition, yet it remains poorly understood. A highly tractable in vitro reaction provided by a resurrected transposase, Hsmar 1, has presented an opportunity to investigate the mechanism adopted by mariners. Transposition relies on the formation of a synaptic complex which, unusually, is assembled asymmetrically. A transposase dimer binds one end of the transposon and recruits a naked end within this complex. Binding of the second end is slow and can be accelerated by juxtaposition of the ends in the right-handed geometry of negative supercoiling nodes. This provides mariner with topological selectivity towards the configuration of recombining partners. In the presence of an excess of transposase the slow rate of synapsis also introduces a competition between transposases dimers for recruiting a free transposon end. This is the basis of a characteristic auto-regulatory mechanism which mariner elements probably take advantage of to limit the extent of a genomic invasion. Within the transpososome, the two strands of a transposon end are cleaved by the same active site. First, the non-transferred strands are cleaved at both ends. Then, a structural transition which is coordinated at the two ends of the complex relocates the active sites onto the transferred strands. Cleavage of the transferred strands exposes 3' -hydroxyls which are transferred 5' of a target TA dinucleotide. The tightly coupled sequence of events, dictated by the architecture of the transpososome, allows a single transposase dimer to complete transposition without recourse to the hairpin mechanism. This provides the first example of a DDE/D enzyme where the active site performs two sequential hydrolyses of DNA strands of opposite polarity. Biological implications of the strategy adopted by mariner elements are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available