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Transposition of a deoxyribonucleic acid sequence encoding trimethoprim and streptomycin resistances from R483 to
Abstract:
R483, a plasmid of the Ialpha incompatibility group, contained a deoxyribonucleic acid (DNA) sequence encoding resistance to trimethoprim (TpR) and streptomycin (SmR) that could be transposed to other replicons, i.e., to the Escherichia coli chromosome and to related and unrelated plasmids. Each transposition resulted in the acquisition by the recipient replicon of a segment of DNA of about 9 X 10(6) daltons, both resistance genes, but never the colicin Ia or pilus genes of R483. Transposition took place at a single chromosomal site between dnaA and ilv and did not suppress the DnaA phenotype, in contrast to integration of the whole R483 plasmid. The chromosome, having received the transposition, could secondarily act as a transposition donor to another plasmid. Such a plasmid was indistinguishable from one having received a direct transposition from R483. TpR SmR transposition was very site specific and did not require a functional recA+ gene. We postulate that the TpR SmR segment of R483 is a transposon (TnC) with specific boundary sequences.
Insights
A DNA segment from the R483 plasmid, conferring trimethoprim and streptomycin resistance, can move to new locations like the E. coli chromosome or other plasmids. This transposon, named TnC, moves specifically without needing the recA+ gene.
Area of Science:
- Molecular biology
- Genetics
- Microbiology
Background:
- The R483 plasmid belongs to the Ialpha incompatibility group.
- R483 harbors DNA sequences for trimethoprim resistance (TpR) and streptomycin resistance (SmR).
Purpose of the Study:
- To investigate the transposition of TpR and SmR genes from the R483 plasmid.
- To characterize the recipient sites and mechanism of transposition.
Main Methods:
- Experiments involving transposition of the R483 plasmid's DNA segment to E. coli chromosome and other plasmids.
- Analysis of the acquired DNA segment size and gene content in recipient replicons.
- Assessment of the impact on recipient phenotypes and secondary transposition events.
Main Results:
- The TpR SmR DNA segment, approximately 9 x 10(6) daltons, transposed to E. coli chromosome and other plasmids, excluding colicin Ia or pilus genes.
- Transposition occurred at a specific site on the E. coli chromosome (between dnaA and ilv) without affecting the DnaA phenotype.
- The modified chromosome could act as a secondary donor for transposition to another plasmid.
- Transposition was highly site-specific and independent of the recA+ gene.
Conclusions:
- The TpR SmR segment of R483 functions as a transposon (TnC) with distinct boundary sequences.
- TnC exhibits site-specific integration and can mediate further transposition events.
- The recA+ gene is not required for TnC transposition.