imported>GPbernet at 14:41, 3 October 2011

2011-10-03T14:41:35Z

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Transposases (TRs) are often referred as the enzymes codified in DNA transposons (Class II of transposable elements) involved in double-strand DNA transposition from one location to another in the host genome ("cut and paste" mechanism).

Generically, TRs are DNA-binding enzymes that catalyze “cut and paste” or “copy and paste” reactions to promote the movement of DNA sequences ([[literature:100832|Rice and Baker 2001]]). TRs belong to the polynucleotidyl transferase superfamily which includes [[Ribonuclease_H|RNase H]], RuvC resolvase, RAG proteins and retroviral [[integrase| Integrases]] ([[literature:100833|Nesmelova and Hackett 2010]]).

Transposase enzymes are divided into several families based on the mechanism utilized during transposition ([[literature:100833|Nesmelova and Hackett 2010]]; [[literature:100834|Curcio and Derbyshire 2001]]; [http://www.ebi.ac.uk/interpro/potm/2006_12/Page1.htm InterPro 2006]):

* Tyrosine (Y)-TRs
* Serine (S)-TRs
* Rolling-circle (RC), or Y2-TRs
* Reverse transcriptases/endonucleaseses (RT/En)
* DDE-TRs

DDE-TRs contain a characteristic triad of conserved amino acids: Asp (D), Asp (D) and Glu (E) (this third residue can also be Asp in some cases), and a common structural motif, RNase H-like fold, bringing these three residues into close proximity to form a catalytic pocket containing two divalent metal ions that assist in the various nucleophilic reactions during DNA cleavage ([[literature:30832|Hickman ''et al''. 2005]]).

<center>[[File: Transposase.png]]</center>
<center>3D structure the catalytic domain of ''Mos1'' mariner TR adapted from the PDB-file [http://www.pdb.org/pdb/explore.do?structureId=2F7T 2F7T]</center>

DDE-TRs catalyze DNA sequence transposition after recognizing and joining to DNA-binding domains to form the synaptic protein-DNA complex. Then the mobilized DNA is excised by means of the hydrolysis of the phosphodiester bonds at each end to generate free 3′-OH groups. Finally, these free groups are joined to the target DNA sequence through a single-step transesterification.

<center>[[File: Trmechanism3.png]]</center>

<center>Schematic representation of DDE TRs mechanism of transposition</center>

Beyond this overall view and common shared features, DDE TRs, and TRs in general, show a great degree of variability at different levels. DNA-binding domain specific recognition, synaptic complex organization (dimeric, tetrameric…) and mechanisms of DNA cleavage and interaction can vary widely depending on the particular TR.

Transposase - Revision history

imported>GPbernet at 14:41, 3 October 2011