Summary A fused F prime factor was obtained from a mating of a
recA donor carrying an F' factor containing the genes
metBJF, ppc and
argECBH (KLF5) with a
recA recipient carrying an F' factor containing
att80, trp and
lac (F155). Lysogenization of this fused F-prime factor with cI
857 h80 phage followed by thermoinduction produced the transducing phages 80
dmetBJF and 80
dppcargECBH. This kind of fusion provides a general procedure for the construction of transducing phages carrying genes from different regions of the
E. coli genome. To understand the mechanism of this fusion, the parental F prime factors (F155 and KLF5) were analyzed by the electron microscope heteroduplex technique.F155 has a length of 176±3 kilobases including two substitutions. The F sequence 0 F-2.8 F has been substituted by 53 kb of chromosomal DNA including the
lac operon and the F sequences 8.5 F-16.3 F has been substituted by 27 kb of a chromosomal sequence including
att80 and the
trp operon.KLF5 contains 221±4 kilobases of DNA (molecular weight, 148 megadaltons). It contains complete F and the segment of the
E. coli chromosome from
polA to
rif. The F sequence 2.8 F-8.5 F known to be involved in F specific recombination in
recA
+ and
RecA backgrounds occurs twice on KLF5, once at each of the junctions of F DNA with chromosomal DNA. The population of closed circular plasmid molecules extracted from KLF5-containing strains is heterogeneous. It is proposed that this heterogeneity is due to intramolecular recombination events occurring in KLF5 between the duplicated 2.8 F-8.5 F sequences. Such recombination can account for the genetic instability of KLF5 observed in both
recA
+ and
recA hosts. The F sequence 2.8 F-8.5 F (also called ) is one of the characterized integration sequences on F.A model for the fusion of the parental F prime factors is proposed in which recombination between sequences brings
att80 close to the
metBJF genes. This is followed by a deletion of an F'
lac factor. The resulting fused F' factor still carries two sequences and is therefore expected to be unstable. The closed circular molecules isolated from the fused F' containing strains show two different sizes of molecules. Genetic and physical analyses of these molecules are in agreement with the predicted instability of the fused F' factor and the existance of the sequence in the 80
dmet phages isolated from fused F' and previously analyzed by the electron microscope heteroduplex technique.
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