Nucleic Acids Research Advance Access published online on June 18, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn056
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Methods Online |
Quick identification of Type I restriction enzyme isoschizomers using newly developed pTypeI and reference plasmids
1Division of Microbiology and Molecular Genetics, Department of Biochemistry and Microbiology and 2Department of Pathology and Laboratory Medicine, School of Medicine, Loma Linda University, Loma Linda, CA92350, USA
*To whom correspondence should be addressed. Email: erowsell{at}llu.edu
Received December 30, 2007. Revised January 24, 2008. Accepted January 25, 2008.
Although DNA-recognition sequences are among the most important characteristics of restriction enzymes and their corresponding methylases, determination of the recognition sequence of a Type-I restriction enzyme is a complicated procedure. To facilitate this process we have previously developed plasmid R-M tests and the computer program RM search. To specifically identify Type-I isoschizomers, we engineered a pUC19 derivative plasmid, pTypeI, which contains all of the 27 Type-I recognition sequences in a 248-bp DNA fragment. Furthermore, a series of 27 plasmids (designated reference plasmids), each containing a unique Type-I recognition sequence, were also constructed using pMECA, a derivative of pUC vectors. In this study, we tried those vectors on 108 clinical E. coli strains and found that 48 strains produced isoschizomers of Type I enzymes. A detailed study of 26 strains using these reference plasmids revealed that they produce seven different isoschizomers of the prototypes: EcoAI, EcoBI, EcoKI, Eco377I, Eco646I, Eco777I and Eco826I. One strain EC1344 produces two Type I enzymes (EcoKI and Eco377I).
I regret to inform our readers that Dr Junichi Ryu died before publication of this article.