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Multistep transduction of tryptophan (trp) genes in Escherichia coli
Published online by Cambridge University Press: 14 April 2009
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Plaque-forming transducing (pt) particles of bacteriophage ø 80 have been used to transduce genes governing tryptophan synthesis. Main interest was devoted to strains which carry deletions extending for varying distances into the tryptophan (trp) operon, covering trp A and ending in trp B, trp C or further. If the deletion does not over-reach trp C, infection by pt particles carrying the trp (CBA)+ segment gives rise to stable partial diploids which express the complete tryptophan independence. If the deletion is further extended, transductants are not entirely complemented and appear only on medium containing indole. If the recipients do not carry any prophage in the attachment site of ø 80 (att80) the indole-requiring transductants are very unstable; if the recipients do carry such prophage, even defective, all transductants are very stable. Stable indole-requiring diploids can be superinfected by other pt phages carrying the complementary genes of the tryptophan operon, giving rise to supertransduced indole-independent bacteria. Transduction to complete independence of tryptophan or any precursor has also been achieved in three steps. Supertransductants yield after u.v. induction pt phages carrying the initial trp segments and segregate rare cells with incomplete ability to synthesize tryptophan. They are therefore polylysogenic polyploid heterogenotes carrying overlapping segments of the trp operon linked to prophage genomes.
When recipients are carrying a prophage in att80, transductants appear at a low frequency. The reduction is particularly pronounced with ø 80 pt transducing segment trp (CBA)+ to immune bacteria.
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- Copyright © Cambridge University Press 1968
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