Substitution of 5-methylcytosines for cytosines enhances the stability of topoisomerase I-DNA complexes and modulates the sequence selectivity of camptothecin-induced DNA cleavage.
We have investigated the binding and cleavage of DNA by human topoisomerase I using a 160 bp restriction fragment containing either natural bases or 5-methylcytosine residues in place of cytosines. Experiments were performed in the presence and absence of the antitumour drug camptothecin which specifically inhibits topoisomerase I. Replacement of all cytosines with 5-methylcytosine residues (i) reinforces the enzyme-DNA interaction, (ii) enhances the stability of topoisomerase I-DNA complexes and (iii) modulates the sequence selectivity of camptothecin-induced DNA cleavage. The methyl group exposed in the major groove of the double helix is identified as a critical element for the interaction between topoisomerase I and DNA.
Carrasco
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C
Laboratoire de Pharmacologie Antitumorale du Centre Oscar Lambret et INSERM U-124, IRCL, Lille, France.
Waring
M J
MJ
Bailly
C
C
D044503:5-Methylcytosine; D001483:Base Sequence; D002166:Camptothecin / Q000378:metabolism*; D003596:Cytosine / Q000031:analogs & derivatives* / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D013329:Structure-Activity Relationship
D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin