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FEBS Lett. 2011 Apr 20;585(8):1216-22. doi: 10.1016/j.febslet.2011.03.043. Epub 2011 Mar 23.

Tyrosine partners coordinate DNA nicking by the Salmonella typhimurium plasmid pCU1 relaxase enzyme.

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  • 1Department of Chemistry, Caudill and Kenan Laboratories, CB 3290, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA.


Conjugative plasmid transfer results in the spread of antibiotic resistance genes and virulence factors between bacterial cells. Plasmid transfer is dependent upon the DNA nicking activity of a plasmid-encoded relaxase enzyme. Tyrosine residues within the relaxase cleave the DNA plasmid nic site in a highly sequence-specific manner. The conjugative resistance plasmid pCU1 encodes a relaxase with four tyrosine residues surrounding its active site (Y18,19,26,27). We use activity assays to demonstrate that the pCU1 relaxase preferentially uses Y26 or a combination of Y18 + 19 to nick DNA at wild type levels, and that an adjacent aspartic acid deprotonates these tyrosines to activate them for attack. Our findings illustrate the unique modifications that the pCU1 relaxase has introduced into the traditional relaxase-mediated DNA nicking mechanism.

Copyright © 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

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