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. 1990 Aug;172(8):4263–4270. doi: 10.1128/jb.172.8.4263-4270.1990

Characterization of the F-plasmid conjugative transfer gene traU.

D Moore 1, K Maneewannakul 1, S Maneewannakul 1, J H Wu 1, K Ippen-Ihler 1, D E Bradley 1
PMCID: PMC213250  PMID: 2198250

Abstract

We characterized the traU gene of the Escherichia coli K-12 conjugative plasmid F. Plasmids carrying segments of the F transfer operon were tested for their capacity to complement F lac traU526. The protein products of TraU+ clones were identified, and the nucleotide sequence of traU was determined. traU mapped between traW and trbC. It encodes a 330-amino-acid, Mr36,786 polypeptide that is processed. Ethanol caused accumulation of a precursor polypeptide; removal of ethanol permitted processing of the protein to occur. Because F lac traU526 strains appear to be resistant to F-pilus-specific phages, traU has been considered an F-pilus assembly gene. However, electron microscopic analysis indicated that the traU526 amber mutation caused only a 50% reduction in F-piliation. Since F lac traU526 strains also retain considerable transfer proficiency, new traU mutations were constructed by replacing a segment of traU with a kanamycin resistance gene. Introduction of these mutations into a transfer-proficient plasmid caused a drastic reduction in transfer proficiency, but pilus filaments remained visible at approximately 20% of the wild-type frequency. Like traU526 strains, such mutants were unable to plaque F-pilus-specific phages but exhibited a slight sensitivity on spot tests. Complementation with a TraU+ plasmid restored the wild-type transfer and phage sensitivity phenotypes. Thus, an intact traU product appears to be more essential to conjugal DNA transfer than to assembly of pilus filaments.

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Selected References

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