On the viability of Escherichia colicells lacking DNA topoisomerase I

BMC Microbiology

Research Article

Robert G Lloyd¹  Christian J Rudolph²  Anna Stockum³ 

[1] Centre for Genetics and Genomics, University of Nottingham, Queen's Medical Centre, NG7 2UH, Nottingham, UK;Centre for Genetics and Genomics, University of Nottingham, Queen's Medical Centre, NG7 2UH, Nottingham, UK;Division of Biosciences, School of Health Sciences and Social Care, Brunel University London, UB8 3PH, Uxbridge, UK;Centre for Genetics and Genomics, University of Nottingham, Queen's Medical Centre, NG7 2UH, Nottingham, UK;Division of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, W2 1PG, London, UK;

关键词: Growth Defect;    White Coloni;    Compensatory Mutation;    topA Gene;    Torsional Stress;   

DOI  :  10.1186/1471-2180-12-26

 received in 2011-11-09, accepted in 2012-02-28,  发布年份 2012

来源: Springer

【 摘 要 】

BackgroundManipulations of the DNA double helix during replication, transcription and other nucleic acid processing cause a change of DNA topology, which results in torsional stress. This stress is relaxed by DNA topoisomerases, a class of enzymes present in all domains of life. Negatively supercoiled DNA is relaxed by type IA topoisomerases that are widespread in bacteria, archaea and eukaryotes. In Escherichia coli there is conflicting data about viability of ΔtopA cells lacking topoisomerase I.ResultsIn this study we sought to clarify whether E. coli cells lacking topoisomerase I are viable by using a plasmid-based lethality assay that allowed us to investigate the phenotype of ΔtopA cells without the presence of any compensatory mutations. Our results show that cells lacking topoisomerase I show an extreme growth defect and cannot be cultured without the accumulation of compensatory mutations. This growth defect can be partially suppressed by overexpression of topoisomerase III, the other type IA topoisomerase in E. coli, suggesting that the accumulation of torsional stress is, at least partially, responsible for the lethality of ΔtopA cells. The absence of RNase HI strongly exacerbates the phenotype of cells lacking topoisomerase I, which supports the idea that the processing of RNA:DNA hybrids is vitally important in ΔtopA cells. However, we did not observe suppression of the ΔtopA phenotype by increasing the level of R-loop processing enzymes, such as RNase HI or RecG.ConclusionsOur data show unambiguously that E. coli cells are not viable in the absence of DNA topoisomerase I without the presence of compensatory mutations. Furthermore, our data suggest that the accumulation of R-loops is not the primary reason for the severe growth defect of cells lacking topoisomerase I, which is in contrast to the current literature. Potential reasons for this discrepancy are discussed.

【 授权许可】

Unknown   
© Stockum et al; licensee BioMed Central Ltd. 2012. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.