title: Bifunctional TaqII restriction endonuclease: redefining the prototype DNA recognition site and establishing the Fidelity Index for partial cleaving.
abstract: BACKGROUND
  The TaqII enzyme is a member of the Thermus sp. enzyme family that we propounded previously within Type IIS restriction endonucleases, containing related thermophilic bifunctional endonucleases-methyltransferases from various Thermus sp.: TaqII, Tth111II, TthHB27I, TspGWI, TspDTI and TsoI. These enzymes show significant nucleotide and amino acid sequence similarities, a rare phenomenon among restriction endonucleases, along with similarities in biochemical properties, molecular size, DNA recognition sequences and cleavage sites. They also feature some characteristics of Types I and III.
  
  
  RESULTS
  Barker et al. reported the Type IIS/IIC restriction endonuclease TaqII as recognizing two distinct cognate site variants (5'-GACCGA-3' and 5'-CACCCA-3') while cleaving 11/9 nucleotides downstream. We used four independent methods, namely, shotgun cloning and sequencing, restriction pattern analysis, digestion of particular custom substrates and GeneScan analysis, to demonstrate that the recombinant enzyme recognizes only 5'-GACCGA-3' sites and cleaves 11/9 nucleotides downstream. We did not observe any 5'-CACCCA-3' cleavage under a variety of conditions and site arrangements tested. We also characterized the enzyme biochemically and established new digestion conditions optimal for practical enzyme applications. Finally, we developed and propose a new version of the Fidelity Index - the Fidelity Index for Partial Cleavage (FI-PC).
  
  
  CONCLUSIONS
  The DNA recognition sequence of the bifunctional prototype TaqII endonuclease-methyltransferase from Thermus aquaticus has been redefined as recognizing only 5'-GACCGA-3' cognate sites. The reaction conditions (pH and salt concentrations) were designed either to minimize (pH = 8.0 and 10 mM ammonium sulphate) or to enhance star activity (pH = 6.0 and no salt). Redefinition of the recognition site and reaction conditions makes this prototype endonuclease a useful tool for DNA manipulation; as yet, this enzyme has no practical applications. The extension of the Fidelity Index will be helpful for DNA manipulation with enzymes only partially cleaving DNA.
authors.affiliation: Institute for Environmental and Human Health Protection, Department of Chemistry University of Gdańsk, Gdańsk, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Zylicz-Stachula
authors.forename: Olga
authors.initials: O
authors.lastname: Zołnierkiewicz
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Sliwińska
authors.forename: Joanna
authors.initials: J
authors.lastname: Jeżewska-Frąckowiak
authors.forename: Piotr M
authors.initials: PM
authors.lastname: Skowron
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D013379:Substrate Specificity; D013824:Thermus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004247:DNA; C042367:endodeoxyribonuclease TaqII; D015252:Deoxyribonucleases, Type II Site-Specific