DNA bending induced by six DNA (cytosine-5) methyltransferases was studied using circular permutation gel mobility shift assay. The following bend angles were obtained: M.BspRI (GGm5CC), 46-50°; M.HaeIII (GGm5CC), 40-43°; M.SinI (GGWm5CC), 34-37°; M.Sau961 (GGNm5CC), 52-57°; M.HpaII (Cm5CGG), 30°; and M.Hhal (Gm5CGC), 13°. M.HaeIII was also tested with fragments carrying a methylated binding site, and it was found to induce a 32°bend. A phasesensitive gel mobility shift assay, using a set of DNA fragments with a sequence-directed bend and a single methyltransferase binding site, indicated that M.HaeIII and M.BspRI bend DNA toward the minor groove. The DNA curvature induced by M.HaeIII contrasts with the lack of DNA bend observed for a covalent M.HaeIII-DNA complex in an earlier X-ray study. Our results and data from other laboratories show a correlation between the bending properties and the recognition specificities of (cytosine-5) methyltransferases: enzymes recognizing a cytosine 3' to the target cytosine tend to induce greater bends than enzymes with guanine in this position. We suggest that the observed differences indicate different mechanisms employed by (cytosine-5) methyltransferases to stabilize the helix after the target base has flipped out.
|Number of pages||9|
|Journal||Nucleic acids research|
|Publication status||Published - aug. 15 2000|
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