Transduction of R factors with phage P1 from recombination-deficient Escherichia coli.

Abstract

In the transduction of R factor with phage P1 from rec− host, transduction frequency was less than that from the rec+ host but no segregation of resistance markers took place. However, a low percent of segregation was found in the transduction from rec+ host. In contrast, phage particles of small size contained in P1 lysate could not transduce R factor even from a rec+ host, although they could transduce chromosomal markers as did the usual P1 lysate. Recombination of the R factor took place in the rec− host at a frequency similar to the rec− host. Considering from the results that P1 is capable of transducing a DNA fragment of the same size as that of phage P1, it was concluded that the molecular weight of R factor DNA is smaller than that of phage P1 (6×107 daltons) but larger than that of small P1 particle (2.4×107 daltons). When transduced with phage P1, the R factor genome has to become a DNA fragment of the same size as the P1 particle by addition of other DNA following the recombination between R factor and Pl in rec+ host. Hence, the segregation of markers of the R factor takes place on occasion by this recombination. From the assumption that phage Pl cannot recombine with the R factor in rec− host, it was predicted that the R factor genome becomes a DNA fragment of large enough size for transduction with P1 by polymerization of the R genome itself. This possibly could explain the decrease in transduction frequency from a rec− host and no segregation of the resistance markers of R factor in transduction from rec− host.