Regulation of the function of eukaryotic DNA topoisomerase I: topological conditions for inactivity.
The effects of supercoiling on the cleavage reaction by eukaryotic DNA topoisomerases I (wheat germ, chicken erythrocyte, and calf thymus) have been analyzed on DNA fragments (0.96 and 2.3 kilobases) encompassing an immunoglobulin kappa light-chain promoter. In one topological condition of the substrate, the absolutely relaxed state, cleavage was found to be impeded. This finding defines the topology-dependent step of the eukaryotic DNA topoisomerase I reaction and shows that for the cleavage reaction topology is more critical than sequence effects. These findings suggest a simple model for the regulation of the DNA topoisomerase I reaction based on topological factors, which may explain the regulatory function of the enzyme in in vivo eukaryotic transcription.
Camilloni
G
G
Centro Acidi Nucleici, Consiglio Nazionale della Ricerche, Rome, Italy.
Di Martino
E
E
Di Mauro
E
E
Caserta
M
M
D000818:Animals; D002021:Buffers; D002417:Cattle; D002645:Chickens; D004247:DNA / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism*; D007145:Immunoglobulin kappa-Chains / Q000235:genetics; D007700:Kinetics; D009690:Nucleic Acid Conformation; D010944:Plants / Q000201:enzymology; D011401:Promoter Regions, Genetic; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013696:Temperature; D014908:Triticum
D002021:Buffers; D004278:DNA, Superhelical; D007145:Immunoglobulin kappa-Chains; D004247:DNA; D004264:DNA Topoisomerases, Type I