INTERACTION OF HUMAN DNA TOPOISOMERASE-I WITH SPECIFIC SEQUENCE OLIGODEOXYNUCLEOTIDES

The interaction of human DNA topoisomerase I (topo I) with specific se quence oligodeoxynucleotides (ODNs) of different length and structure has been investigated. All the ODNs used were shown to be effective en zyme inhibitors and to inhibit the topo I catalyzed relaxation of scDN A in a competitive manner. Among two DNA regions (A and B) required fo r topo I-mediated DNA cleavage, the former was found to display the hi gher affinity for the enzyme. The enzyme's affinity for ODNs correspon ding to the scissile strand (five and nine nucleotide units in length) is about 2-4 orders of magnitude higher than that for non-specific OD Ns of the same length. Topo I can efficiently recognize even extremely short specific ODNs containing only two or three bases (AGA and pAG, K-i = 15 and 60 mu M, respectively): the sequence AAGA (K-i = 10 mu M) is essential for tight DNA binding to topo I. The affinities of ODNs corresponding to the non-scissile strand are significantly lower. The ligand's affinity increases with its length. Additionally, about a ten -fold enhancement of specific sequence affinity occurs due to stable d uplex formation during enzyme preincubation with ligands before additi on of scDNA. We believe the possibility of using the short specific ol igonucleotides and its derivatives as topoisomerase I-targeting drugs could not be excluded. (C) Societe francaise de biochimie et biologic moleculaire/Elsevier, Paris.