Enrichment and depletion of Hela topoisomerase I recognition sites among specific types of DNA elements.
The SDS-induced nicking of DNA helix by Hela topoisomerase I in vitro has been studied by using 2.9 kb of cloned human DNA as the substrate. The frequency of nicking is increased from 1/23 (nick/nt) to 1/19 (nick/nt) when camptothecin is present in the nicking reaction. The cytotoxic drug also induces DNA nicks without the addition of SDS. Although the consensus built from DNA sequences from -20 to +20 of more than one hundred of the nicking sites only shows a preference for T at position -1, the distributions of the topoisomerae I-cleavable sites among different categories of specific DNA sequences are apparently non- random. Long stretches of tandem (CA), A, or T residues, and the GC-rich promoter region of alpha 1 globin gene are all refractory to the nicking reaction. However, the nicking frequencies of short direct repeats flanking different Alu type sequences are as high as 1/6 (nick/nt). Finally, several tandemly arranged minirepeats of the form (TxAy)z, that are usually found at the 3' ends of the primate Alu family or Kpnl family repeats, can be cleaved efficiently in a regular pattern by the enzyme. These data are discussed in terms of the mode of recognition of DNA sequences/structures by topoisomerase I, and its possible roles in the nonhomologous insertion of repetitive DNA sequences.
Perez-Stable
C
C
Department of Genetics, University of California, Davis 95616.
Shen
C C
CC
Shen
C K
CK
D000328:Adult; D001483:Base Sequence / Q000187:drug effects; D002166:Camptothecin / Q000633:toxicity; D004249:DNA Damage; D004262:DNA Restriction Enzymes / Q000235:genetics / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D005914:Globins / Q000235:genetics; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000187:drug effects; D012091:Repetitive Sequences, Nucleic Acid / Q000187:drug effects; D012967:Sodium Dodecyl Sulfate
D012967:Sodium Dodecyl Sulfate; D005914:Globins; D004262:DNA Restriction Enzymes; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin