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A ColE1-type plasmid from Salmonella enteritidis encodes a DNA cytosine methyltransferase
M Ibáñez1, I Alvarez, J M Rodríguez-Peña
1Departamento de Microbiologia II, Facultad de Farmacia, Universidad Complutense, Madrid, Spain.
Abstract:
The multicopy plasmid pFM366 was isolated from a virulent Salmonella enteritidis strain and was found to code for DNA methylase activity (Ibáñez and Rotger, 1993). The present work was aimed at characterizing the genetic organization and functional features of this 5.6 kb plasmid. We found pFM366 almost identical to the plasmid P4 isolated from Shigella sonnei, that encodes the SsoII restriction-modification system (Karyagina et al., 1993), and related to other ColE1-type plasmids. Examination of these plasmids revealed a common organization which suggests they were the result of similar recombinational events. The cytosine methylase of pFM366 is nearly identical to M. SsoII, whereas the gene encoding the restrictase homologous to R. SsoII is truncated and its product is inactive. The expression of the cytosine methylase encoded by pFM366 is strongly affected by deletion of regions located upstream and downstream of its ORF, and is negatively controlled by the rpoS gene in Escherichia coli. The methylase activity encoded by pFM366 induces the SOS response, which could be responsible for the observed delay in the growth of E. coli.
Insights
The pFM366 plasmid from Salmonella enteritidis contains a DNA methylase. Its activity is regulated by upstream/downstream regions and the rpoS gene, potentially inducing an SOS response in E. coli.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- The multicopy plasmid pFM366, isolated from Salmonella enteritidis, exhibits DNA methylase activity.
- This plasmid shares similarities with ColE1-type plasmids and the SsoII restriction-modification system found in Shigella sonnei.
Purpose of the Study:
- To characterize the genetic organization and functional aspects of the 5.6 kb pFM366 plasmid.
- To investigate the relationship between pFM366 and other related plasmids, suggesting common evolutionary origins.
Main Methods:
- Comparative sequence analysis of pFM366 with related plasmids.
- Functional analysis of the methylase gene, including deletion studies and investigation of regulatory elements.
- Assessment of the impact of methylase activity on host cell physiology (e.g., growth, SOS response).
Main Results:
- pFM366 is highly similar to plasmid P4 from Shigella sonnei, encoding a functional cytosine methylase (M. SsoII homolog) and a truncated, inactive restrictase (R. SsoII homolog).
- Expression of the pFM366 methylase is influenced by flanking DNA regions and negatively regulated by the rpoS gene in E. coli.
- The methylase activity triggers the SOS response in E. coli, correlating with a delay in bacterial growth.
Conclusions:
- pFM366 represents a functional DNA methylase system with potential implications for bacterial physiology and evolution.
- The findings suggest that pFM366 and related plasmids may have arisen from similar recombination events.
- The induction of the SOS response by pFM366 methylase activity warrants further investigation into its role in bacterial adaptation and virulence.