title: Fragmentation of replicating chromosomes triggered by uracil in DNA.
abstract: The dut mutants of Escherichia coli fail to hydrolyze dUTP and thus incorporate uracil into their DNA, suffering from chromosomal fragmentation. The postulated mechanism for the double-strand DNA breaks is clustered uracil excision, which requires high density of DNA-uracils. However, we did not find enough uracil residues or excision nicks in the DNA of dut mutants to account for clustered uracil excision. Using a dut recBC(Ts) mutant of E.coli to inquire into the mechanism of uracil-triggered chromosomal fragmentation, we show that this fragmentation requires DNA replication and, in turn, inhibits replication of the chromosomal terminus. As a result, origin-containing sub-chromosomal fragments accumulate in dut recBC conditions, indicating preferential demise of replication bubbles. We propose that the basic mechanism of the uracil-triggered chromosomal fragmentation is replication fork collapse at uracil-excision nicks. Possible explanations for the low level terminus fragmentation are also considered.
authors.affiliation: Department of Microbiology, University of Illinois at Urbana-Champaign, 601 South Goodwin Ave., Urbana, IL 61801-3709, USA.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Kouzminova
authors.forename: Andrei
authors.initials: A
authors.lastname: Kuzminov
mesh_terms: D001483:Base Sequence; D048750:Cell Nucleus Division; D019457:Chromosome Breakage; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D004261:DNA Replication; D004926:Escherichia coli / Q000235:genetics; D043211:Exodeoxyribonuclease V / Q000378:metabolism; D014498:Uracil / Q000378:metabolism
chemical_list: D014498:Uracil; D004247:DNA; D043211:Exodeoxyribonuclease V