Gamma-Delta or Transposon Tn1000 forms Unstable F-Prime Plasmid KLF-5 in the Proximity of Oric

Abstract

The F prime plasmid KLF5 consists of two components, one component is F plasmid (100Kb) and the other component is chromosomal segment of length 125Kb containing metBJF and argECBH operons, is unusually unstable. The parent of this KLF5 is an Hfr donor Ra-2, an E.coli K-12 derivative in which F is integrated into the chromosome at a site, probably gamma delta which is proximal to the oriC. Such an integration of F occurs by a cross-over between gamma delta of F and the copy of gamma delta prevailing in the chromosome (sfa site). Duplication of gamma delta (Tn1000), one copy at each junction of the F and the E.coli K12 chromosome. The Hfr Ra-2 thus formed is unstable. F factor becomes RTF first by the self- deletion effect of gamma –delta (2.8F -8.5F) to transpose into the F oriV at 42.5F. In such genetic event the RTF (replicon) alters few bases and then associates with available transposons via IS1 (duplicated in a direct order). These transposons are not just antibiotic resistance determinants of R plasmid but transposons which can translocate into any site on the same chromosome (spontaneous mutations)! Such an R plasmid confers on its host bacterium Shigella flexneri an ability to survive in penicillin or ampicillin. We dare now to predict that F replicon has become R replicon (RTF) by a subtle change in the oriV region of Dr Lederberg’s F plasmid.