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DNA binding and cleavage selectivity of the Escherichia coli DNA G:T-mismatch endonuclease (vsr protein)

Lookup NU author(s): Dr David Turner, Professor Bernard Connolly


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The Escherichia coli vsr endonuclease recognises T:G base-pair mismatches in double-stranded DNA and initiates a repair pathway by hydrolysing the phosphate group 5′ to the incorrectly paired T. The gene encoding the vsr endonuclease is next to the gene specifying the E. coli dcm DNA-methyltransferase; an enzyme that adds CH3 groups to the first dC within its target sequence CC[A/T]GG, giving C5MeC[A/T]GG. Deamination of the d5MeC results in CT[A/T]GG in which the first T is mis-paired with dG and it is believed that the endonuclease preferentially recognises T:G mismatches within the dcm recognition site. Here, the preference of the vsr endonuclease for bases surrounding the T:G mismatch has been evaluated. Determination of specificity constant (kst/KD; kst = rate constant for single turnover, KD = equilibrium dissociation constant) confirms vsr's preference for a T:G mismatch within a dcm sequence i.e. CT[A/T]GG (the underlined T being mis-paired with dG) is the best substrate. However, the enzyme is capable of binding and hydrolysing sequences that differ from the dcm target site by a single base-pair (dcm star sites). Individual alteration of any of the four bases surrounding the mismatched T gives a substrate, albeit with reduced binding affinity and slowed turnover rates. The vsr endonuclease has a much lower selectivity for the dcm sequence than type II restriction endonucleases have for their target sites. The results are discussed in the light of the known crystal structure of the vsr protein and its possible physiological role. © 2001 Academic Press.

Publication metadata

Author(s): Gonzalez-Nicieza R, Turner DP, Connolly BA

Publication type: Article

Publication status: Published

Journal: Journal of Molecular Biology

Year: 2001

Volume: 310

Issue: 3

Pages: 501-508

ISSN (print): 0022-2836

ISSN (electronic): 1089-8638

Publisher: Academic Press


DOI: 10.1006/jmbi.2001.4799

PubMed id: 11439018


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