Nucleic Acids Research, Vol 27, Issue 4 1032-1038, Copyright © 1999 by Oxford University Press
MR Rice, MD Koons and RM Blumenthal
The Pvu II restriction endonuclease (R. Pvu II) cleaves CAG downward
arrowCTG sequences as indicated, leaving blunt ends. Its cognate
methyltransferase (M. Pvu II) generates N4-methylcytosine, yielding
CAGN4mCTG, though the mechanism by which this prevents cleavage by R. Pvu
II is unknown. The heterologous 5-methylcytosinemethylation CAG5mCTG has
also been reported to prevent cleavage by R. Pvu II and this has been used
in some cloning methods. Since this heterologousmethylation occurs at the
native methylated base, it can provide insights into the detection of
DNAmethylation by R. Pvu II. We found that the cloned gene for R. Pvu II
could not stably transform cells protected only by M. Alu I (AG5mCT) and
then determined that R. Pvu II cleaves CAG5mCTG in vitro, even when both
strands are methylated. DNase I footprint analysis and competition
experiments reveal that R. Pvu II binds to CAG5mCTG specifically, though
with reduced affinity relative to the unmethylated sequence. These results
provide biochemical support for the publishedstructures of R. Pvu II
complexed with DNA containing CAGCTG and CAG5-iodoCTG and support a model
for how methylation interferes with DNA cleavage by this enzyme.
ARTICLES
Substrate recognition by the Pvu II endonuclease: binding and cleavage of CAG5mCTG sites
Department of Microbiology and Immunology, Medical College of Ohio, 3055 Arlington Avenue, Toledo, OH 43614-5806, USA.
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