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Title: Stx-Phage Integration and Multiple Lysogeny in Escherichia coli
Author: Fogg, Paul C. M.
ISNI:       0000 0001 3471 750X
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2007
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The characteristic virulence factor of shigatoxigenic E. coli strains (STEC) is the expression of Shiga-toxin encoded in the late gene region of temperate lambdoid phages. The use of differentially labelled isogenic recombinant Stx phage (cD24B) had demonstrated the production of true double lysogens in E. coli, contrary to the lambda immunity model, however, the insertion sites and underlying mechanisms had not been determined. Here, the bacteriophage <1>24B integrase gene and the preferred site of insertion in the E. coli genome have been identified. The integrase encoded by <1>24B differs significantly from the integrases of all other previously characterised phages, and the insertion site shares 24 bp of complimentary sequence with the phage aUP site. Furthermore, an additional 3 integration sites in the E. coli genome were elucidated, each with a decreased level of ide'ntity with the aUP site. Triple lysogens could be produced by means of isogenic phage in which the stx gene was interrupted with kanamycin, chloramphenicol and spectinomycin resistance genes as reporters. There were seven possible sites of integration identified, two of which lay within predicted essential genes in the E. coli genome, and thus could not be occupied, and integration at another site was never observed. The preferred integration site described above was close to an integrase gene on the E. coli chromosome but it was demonstrated unequivocally that this host integrase was not responsible for the multiple integration events. The complete partially annotated genome sequence of <1>24B revealed the presence of a gene homologous to the putative antirepressor encoding genes ofVT2-Sa and Lahul and similarity to the well-characterised phage P22 ant gene. Antirepressors bind to the lambdoid phage cI repressor responsible for superinfection immunity and it is therefore possible that the presence of an ant gene on 24B-like. Demonstration of the ability of
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available