The role of topoisomerase IV in partitioning bacterial replicons and the structure of catenated intermediates in DNA replication.
Mutants in bacterial topoisomerase (topo) IV are deficient in chromosomal partitioning. To investigate the basis of this phenotype, we examined plasmid DNA topology in conditionally lethal topo IV mutants. We found that dimeric catenated plasmids accumulated in vivo after topo IV inhibition. The catenanes were supercoiled, contained from 2 to > 32 nodes, and were the products of DNA synthesis. Electron microscopy and recombination tests proved that the catenanes have the unique structure predicted for replication intermediates. These data provide strong evidence for a model in which unlinking of the double helix can occur in two stages during DNA replication and for the critical role of topo IV in the second stage. The interlocks in the catenanes appear to be sequestered from DNA gyrase, perhaps by compartmentalization in an enzyme complex dedicated to partitioning.
Adams
D E
DE
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Shekhtman
E M
EM
Zechiedrich
E L
EL
Schmid
M B
MB
Cozzarelli
N R
NR
D002451:Cell Compartmentation; D004247:DNA / Q000737:chemistry*; D004261:DNA Replication; D027101:DNA Topoisomerase IV; D004264:DNA Topoisomerases, Type I / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics; D008954:Models, Biological; D012093:Replicon; D012486:Salmonella typhimurium / Q000235:genetics
D004247:DNA; D027101:DNA Topoisomerase IV; D004264:DNA Topoisomerases, Type I