%0 Journal Article
%T Accumulation of large non-circular forms of the chromosome in recombination-defective mutants of Escherichia coli
%A Naofumi Handa
%A Ichizo Kobayashi
%J BMC Molecular Biology
%D 2003
%I BioMed Central
%R 10.1186/1471-2199-4-5
%X In order to learn how the recombination processes contribute to generation and processing of the breakage, large (> 2000 kb) linear forms of Escherichia coli chromosome were detected by pulsed-field gel electrophoresis in various recombination-defective mutants. The mutants were analyzed in a rich medium, in which the wild-type strain showed fewer of these huge broken chromosomes than in a synthetic medium, and the following results were obtained: (i) Several recB and recC null mutants (in an otherwise rec+ background) accumulated these huge linear forms, but several non-null recBCD mutants (recD, recC1001, recC1002, recC1003, recC1004, recC2145, recB2154, and recB2155) did not. (ii) In a recBC sbcA background, in which RecE-mediated recombination is active, recA, recJ, recQ, recE, recT, recF, recO, and recR mutations led to their accumulation. The recJ mutant accumulated many linear forms, but this effect was suppressed by a recQ mutation. (iii) The recA, recJ, recQ, recF and recR mutations led to their accumulation in a recBC sbcBC background. The recJ mutation showed the largest amount of these forms. (iv) No accumulation was detected in mutants affecting resolution of Holliday intermediates, recG, ruvAB and ruvC, in any of these backgrounds.These results are discussed in terms of stepwise processing of chromosomal double-strand breaks.Double-strand (ds) breakage of chromosomal DNA is obviously a serious threat to cells because various activities of the chromosome ¨C gene expression, replication and partition ¨C depend on its integrity. However, recent experiments suggest that such chromosomal ds breakage may occur relatively frequently during "normal" growth in several organisms ¨C in bacteria [1,2], yeast [3] and chicken cells [4].In Escherichia coli, spontaneous breakage and degradation of the chromosome associated with a replication fork were predicted from early genetic analysis and were detected under various conditions of altered replication (for review, see
%U http://www.biomedcentral.com/1471-2199/4/5