Genetic inactivation of topoisomerase I suppresses a defect in initiation of chromosome replication in Escherichia coli |
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Authors: | Jacqueline Louarn Jean-Pierre Bouché Josette Patte and Jean-Michel Louarn |
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Institution: | (1) Centre de Recherche de Biochimie et de Génétique cellulaires du C.N.R.S., 118 route de Narbonne, F-31062 Toulouse Cedex, France |
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Abstract: | Summary A strain of Escherichia coli K12 harboring simultaneously the temperature-sensitive dnaA46 mutation and a deletion of the trp-topA-cysB region plates with the same full efficiency at 30° C and 42° C. We have analyzed the possible involvement of the gene coding for topoisomerase I, topA, in this suppression phenomenon. The Ts phenotype was retrieved upon introduction of a plasmid-borne DNA fragment including an active topA gene into this strain, but not upon introduction of the same fragment harboring a topA::Tn1000 insertion. Replication seems to remain DnaA-dependent in the (topA) strain, however, since we have been unable to introduce a dnaA::Tn10 allele. We propose either that the dnaA46 gene product is overproduced and compensates for its thermal inactivation, or that initiation at oriC demands less DnaA protein in the absence of topoisomerase I.Abbreviations Apr
ampicillin resistance
- Cmr
chloramphenicol resistance
- Kmr
Kanamycin resistance
- Str
streptomycin resistance
- Tcr
tetracycline resistance |
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