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Exploring the DNA mimicry of the Ocr protein of phage T7.

TitleExploring the DNA mimicry of the Ocr protein of phage T7.
Publication TypeJournal Article
Year of Publication2012
AuthorsRoberts GA, Stephanou AS, Kanwar N, Dawson A, Cooper LP, Chen K, Nutley M, Cooper A, Blakely GW, Dryden DTF
JournalNucleic Acids Res
Date Published2012 Sep
KeywordsCalorimetry, DNA, DNA Cleavage, DNA Restriction Enzymes, Escherichia coli, Models, Molecular, Molecular Mimicry, Mutation, Site-Specific DNA-Methyltransferase (Adenine-Specific), Viral Proteins

DNA mimic proteins have evolved to control DNA-binding proteins by competing with the target DNA for binding to the protein. The Ocr protein of bacteriophage T7 is the most studied DNA mimic and functions to block the DNA-binding groove of Type I DNA restriction/modification enzymes. This binding prevents the enzyme from cleaving invading phage DNA. Each 116 amino acid monomer of the Ocr dimer has an unusual amino acid composition with 34 negatively charged side chains but only 6 positively charged side chains. Extensive mutagenesis of the charges of Ocr revealed a regression of Ocr activity from wild-type activity to partial activity then to variants inactive in antirestriction but deleterious for cell viability and lastly to totally inactive variants with no deleterious effect on cell viability. Throughout the mutagenesis the Ocr mutant proteins retained their folding. Our results show that the extreme bias in charged amino acids is not necessary for antirestriction activity but that less charged variants can affect cell viability by leading to restriction proficient but modification deficient cell phenotypes.

Alternate JournalNucleic Acids Res.
PubMed ID22684506
PubMed Central IDPMC3439906
Grant List090288/Z/09/ZA / / Wellcome Trust / United Kingdom
B20089 / / Biotechnology and Biological Sciences Research Council / United Kingdom
BB/C511599/1 / / Biotechnology and Biological Sciences Research Council / United Kingdom
GR080463MA / / Wellcome Trust / United Kingdom
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