Integration of donor DNA in bacterial conjugation

Abstract

Conjugation between ¹³C¹⁵N- and ³H-labelled hybrid donors and ¹³C¹⁵N-labelled hybrid recipients of Escherichia coli gives rise to recombinant radioactive DNA of density greater than labelled hybrid. The donor radioactivity is present, in these molecules, in discrete heavy segments covalently attached to the light strand. When light radioactive Hfr cells are mated to heavy F⁻ cells in light medium, the donor label appears, in DNA extracted from the F⁻ cells, in labelled hybrid molecules. The radioactivity in these molecules is exclusively in the light strand. The insertion of donor material is thus restricted to a single newly formed strand of the recipient DNA and double-strand integrations do not occur. A temperature-sensitive recipient containing the dna B mutation ts₄₃ accumulates single-stranded Hfr DNA if mating is carried out at the nonpermissive temperature. The formation of a complementary strand in the recipient does not, therefore, appear to be necessary for continued transfer of Hfr DNA.