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PMID: 22684506 Published · ppublish English Journal Article Research Support, Non-U.S. Gov't

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

Nucleic acids research ·Vol. 40 ·No. 16 ·2012-09-00 ·Pages 8129-43

Roberts GA, Stephanou AS, Kanwar N, Dawson A, Cooper LP, Chen K, Nutley M, Cooper A, Blakely GW, Dryden DT

Abstract

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.

MeSH Terms
Calorimetry DNA/chemistry DNA Cleavage DNA Restriction Enzymes/metabolism Escherichia coli/cytology,genetics,growth & development Models, Molecular Molecular Mimicry Mutation Site-Specific DNA-Methyltransferase (Adenine-Specific)/metabolism Viral Proteins/chemistry,genetics,metabolism
Chemicals
Ocr protein, bacteriophage T7 Viral Proteins DNA DNA modification methylase EcoKI Site-Specific DNA-Methyltransferase (Adenine-Specific) DNA Restriction Enzymes endodeoxyribonuclease EcoKI
Authors & Affiliations
10 authors, click to expand affiliations / ORCID
Roberts Gareth A
EastChem School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh, EH9 3JZ, UK.
Stephanou Augoustinos S
Kanwar Nisha
Dawson Angela
Cooper Laurie P
Chen Kai
Nutley Margaret
Cooper Alan
Blakely Garry W
Dryden David T F
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Article Info
Journal
Nucleic acids research
Abbr.
Nucleic Acids Res
ISSN
1362-4962
DOI
10.1093/nar/gks516
Published
2012-09-00
Epub
2012-00-07
Pages
8129-43
Language
English
Region
England
NLM ID
0411011
PMCID
PMC3439906
Subset
IM
Grants
Biotechnology and Biological Sciences Research Council · B20089 · United Kingdom
Biotechnology and Biological Sciences Research Council · BB/C511599/1 · United Kingdom
Wellcome Trust · 090288/Z/09/ZA · United Kingdom
Wellcome Trust · GR080463MA · United Kingdom
External Links
PubMed source DOI: 10.1093/nar/gks516 PMC Full Text View journal details
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