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tra cistrons and proteins encoded by the Escherichia coli antibiotic resistance plasmid R6-5

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Hybrid plasmids obtained by cloning individual EcoRI and HindIII fragments of the conjugative plasmid, R6-5, were analyzed for their ability to complement transfer-deficient point mutations of Flac. As a result, the locations of 10 tra cistrons were defined on the physical map of R6-5. Two cistrons, traE and traG, are interrupted by EcoRI restriction sites and one cistron, traC, probably contains a HindIII restriction site. The origin of DNA transfer, oriT, was also localized. Surprisingly the hybrid plasmid carrying oriT is mobilized by the F factor as well as by R6-5. The surface exclusion cistrons, traS and traT, were mapped and their biological expression analyzed. A total of 18 proteins encoded by cistrons within the tra region were detected by SDS polyacrylamide gel electrophoresis of proteins synthesized in minicells; they represent about 53% of the coding capacity of the cloned DNA. R6-5 DNA fragments containing the cistrons traC, traE, and traT directed the synthesis of proteins which comigrated during SDS gel electrophoresis with the F-coded proteins previously characterized as TraCp, TraEp, and TraTp. A further two proteins encoded by R6-5 comigrated with F-encoded (but genetically unidentified) proteins whose cistrons map in the corresponding part of the tra region. In contrast, no R6-5 proteins corresponding to F proteins TraAp, TraDp, TraJp, TraMp, 6a or 6c were detected. These results are discussed in relation to known DNA sequence homologies between the F and R6-5 plasmids. A preliminary physical map of the tra region of R6-5 is presented and compared with that of F.

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Correspondence to Mark Achtman.

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Communicated by T. Yura

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Achtman, M., Kušećek, B. & Timmis, K.N. tra cistrons and proteins encoded by the Escherichia coli antibiotic resistance plasmid R6-5. Molec. Gen. Genet. 163, 169–179 (1978). https://doi.org/10.1007/BF00267407

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  • traC
  • EcoRI Restriction
  • Conjugative Plasmid
  • HindIII Fragment
  • HindIII Restriction Site