Characterization of the F-plasmid conjugative transfer gene traU.
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.
Department of Medical Microbiology and Immunology, Texas A&M University, College Station 77840.
D
D
Moore
K
K
Maneewannakul
S
S
Maneewannakul
J H
JH
Wu
K
K
Ippen-Ihler
D E
DE
Bradley
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D000431:Ethanol / Q000494:pharmacology; D005144:F Factor; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon; D014176:Protein Biosynthesis / Q000187:drug effects; D015183:Restriction Mapping
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C065100:TraU protein, E coli; D000431:Ethanol