Deletions at stalled replication forks occur by two different pathways.
Replication blockage induces non-homologous deletions in Escherichia coli. The mechanism of the formation of these deletions was investigated. A pBR322-mini-oriC hybrid plasmid carrying two E. coli replication terminators (Ter sites) in opposite orientations was used. Deletions which remove at least the pBR322 blocking site (named Ter1) occurred at a frequency of 2 x 10(-6) per generation. They fall into two equally large classes: deletions that join sequences with no homology, and others that join sequences of 3-10 bp of homology. Some 95% of the deletions in the former class resulted from the fusion of sequences immediately preceding the two Ter sites, indicating a direct role for blocked replication forks in their formation. These deletions were not found in a topA10 mutant, suggesting a topoisomerase I-mediated process. In contrast, deletions joining short homologous sequences were not affected by the topA10 mutation. However, the incidence of this second class of deletions increased 10-fold in a recD mutant, devoid of exonuclease V activity. This indicates that linear molecules are intermediates in their formation. In addition, approximately 50% of these deletions were clustered in the region flanking the Ter1 site. We propose that they are produced by repair of molecules broken at the blocked replication forks.
Bierne
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Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, Jouy en Josas France.
Ehrlich
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SD
Michel
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B
D001483:Base Sequence; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000235:genetics; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion
D029968:Escherichia coli Proteins; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli; D004264:DNA Topoisomerases, Type I