Asymmetric crossing over in the spontaneous formation of large deletions in the tonB-trp region of the Escherichia coli K-12 chromosome. |
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Authors: | N Uematsu C Matsuoka Y Agemizu E Nagoshi and K Yamamoto |
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Institution: | (1) Biological Institute, Graduate School of Science, Tohoku University, Sendai 980–8578, Japan e-mail: yamamot@mail.cc.tohoku.ac.jp Fax: +81-22-2176706, JP |
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Abstract: | The chromosomal tonB gene of Escherichia coli was used as a target for the detection of spontaneous deletion mutations. The deletions were isolated in both recA
+ and recA
− cells, and mutants carrying large deletions were identified because they also lacked part or all of the trp operon. The frequencies of tonB-trp deletion were 1.79 × 10−9 and 1.09 × 10−9 for recA
+ and recA
− cells, respectively. We analyzed 12 deletions from recA
+ and 10 from recA
− cells by cloning and direct sequencing. The deletions ranged in size from 5612 bp to 15142 bp for recA
+ and from 5428 bp to 13289 for recA
− cells. Three deletions from recA
+ cells and five deletions from recA
− cells were found to have occurred between short sequence repeats at the termini of the deletion, leaving one copy of the
repeat in the mutant sequence. Seven deletions from recA
+ cells and three deletions from recA
− cells did not have repeats at their termini; in these cases, the DNA sequences that are adjacent to the deletion termini
in the wild-type are characterized by short (2–4 bp) repeats. From these results, a model is presented for the generation
of deletion mutations which involves formation of an asymmetric crossover mediated by repeated sequences of 2- to 4-bp.
Received: 14 September 1998 / Accepted: 22 December 1998 |
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Keywords: | Escherichia coli Deletion mutant Illegitimate recombination Repeated sequence Asymmetric crossover |
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