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Variant forms of matrix protein in Escherichia coli B/r bearing N plasmids
Abstract:
Plasmids of the N incompatibility group have been found to decrease or virtually eliminate the synthesis of the 36,500 dalton outer membrane matrix protein of their Escherichia coli B/r hosts (Iyer, R. (1977) Biochim. Biophys. Acta 470, 258--272 and Iyer, R., Darby, V. and Holland, I.B. (1978) FEBS Lett. 85, 127--132) or modify its composition. Although the 34,000 dalton tol G protein is slightly increased in some strains, it is identical in composition to the homologous protein from the plasmidless host. In three of five N+ strains the synthesis of the modified matrix proteins depends on the temperature of cultivation of the strains in which they occur. The alterations to the matrix proteins are non-identical and do not affect the expression of several plasmid-coded functions including those of sensitivity to the N plasmid-specific filamentous bacteriophage IKe (Khatoon, H. and Iyer, R. (1971) Can. J. Microbiol. 17, 669--675), or their interbacterial transfer via conjugation to appropriate recipient strains. Thus, although the significance of the variant matrix proteins in N+ strains with respect to plasmid-mediated functions remains unclear, N plasmids nevertheless provide a convenient system which might be used to elucidate the events that precede the insertion of this protein into the outer membrane of E. coli B/r hosts.
Insights
N plasmids significantly alter the outer membrane matrix protein synthesis in Escherichia coli B/r hosts. These changes, while not affecting plasmid functions, offer a system to study protein insertion into the bacterial outer membrane.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Plasmids of the N incompatibility group are known to affect outer membrane protein synthesis in Escherichia coli B/r.
- Previous studies indicated a decrease or elimination of a 36,500 dalton outer membrane matrix protein.
Purpose of the Study:
- To investigate the impact of N plasmids on the synthesis and composition of outer membrane proteins in E. coli B/r.
- To determine if alterations in matrix proteins affect plasmid-coded functions.
Main Methods:
- Analysis of outer membrane protein synthesis in N plasmid-containing E. coli B/r strains.
- Comparison of matrix protein composition between plasmid-carrying and plasmidless strains.
- Assessment of plasmid-coded functions, including bacteriophage sensitivity and conjugation.
Main Results:
- N plasmids decrease or eliminate the synthesis of a 36,500 dalton outer membrane matrix protein, or modify its composition.
- A 34,000 dalton tol G protein shows a slight increase in some strains but retains identical composition.
- Alterations in matrix proteins are strain-specific, temperature-dependent in some cases, and do not impact plasmid-coded functions.
Conclusions:
- N plasmids induce significant, though not fully understood, alterations in E. coli B/r outer membrane matrix proteins.
- These variant matrix proteins do not interfere with essential plasmid functions like phage sensitivity or transfer.
- N plasmids provide a valuable model system for studying the biogenesis of outer membrane proteins in E. coli.