Single-strand interruptions in replicating chromosomes cause double-strand breaks.
Replication-dependent chromosomal breakage suggests that replication forks occasionally run into nicks in template DNA and collapse, generating double-strand ends. To model replication fork collapse in vivo, I constructed phage lambda chromosomes carrying the nicking site of M13 bacteriophage and infected with these substrates Escherichia coli cells, producing M13 nicking enzyme. I detected double-strand breaks at the nicking sites in lambda DNA purified from these cells. The double-strand breakage depends on (i) the presence of the nicking site; (ii) the production of the nicking enzyme; and (iii) replication of the nick-containing chromosome. Replication fork collapse at nicks in template DNA explains diverse phenomena, including eukaryotic cell killing by DNA topoisomerase inhibitors and inviability of recombination-deficient vertebrate cell lines.
Kuzminov
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Department of Microbiology, University of Illinois, Urbana-Champaign, B103 C&LSL, 601 South Goodwin Avenue, Urbana, IL 61801-3709. kuzminov@life.uiuc.edu
D010582:Bacteriophage lambda / Q000235:genetics; D019457:Chromosome Breakage; D004261:DNA Replication; D004279:DNA, Viral / Q000096:biosynthesis*; D004926:Escherichia coli
D004279:DNA, Viral