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Volume 2012 (2012), Article ID 719092, 12 pages
Research Article

DNA Binding in High Salt: Analysing the Salt Dependence of Replication Protein A3 from the Halophile Haloferax volcanii

Centre for Genetics and Genomics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK

Received 9 May 2012; Accepted 18 June 2012

Academic Editor: Yoshizumi Ishino

Copyright © 2012 Jody A. Winter et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Halophilic archaea maintain intracellular salt concentrations close to saturation to survive in high-salt environments and their cellular processes have adapted to function under these conditions. Little is known regarding halophilic adaptation of the DNA processing machinery, particularly intriguing since protein-DNA interactions are classically salt sensitive. To investigate such adaptation, we characterised the DNA-binding capabilities of recombinant RPA3 from Haloferax volcanii (HvRPA3). Under physiological salt conditions (3 M KCl), HvRPA3 is monomeric, binding 18 nucleotide ssDNA with nanomolar affinity, demonstrating that RPAs containing the single OB-fold/zinc finger architecture bind with broadly comparable affinity to two OB-fold/zinc finger RPAs. Reducing the salt concentration to 1 M KCl induces dimerisation of the protein, which retains its ability to bind DNA. On circular ssDNA, two concentration-dependent binding modes are observed. Conventionally, increased salt concentration adversely affects DNA binding but HvRPA3 does not bind DNA in 0.2 M KCl, although multimerisation may occlude the binding site. The single N-terminal OB-fold is competent to bind DNA in the absence of the C-terminal zinc finger, albeit with reduced affinity. This study represents the first quantitative characterisation of DNA binding in a halophilic protein in extreme salt concentrations.