Drug Resistance of Enteric Bacteria VIII. Chromosomal Location of Nontransferable R Factor inEscherichia coli

The R(21)(TC) factor, obtained by transduction of the R(10)(TC.CM.SM.SA) factor with phage epsilon to group E Salmonella, is not transferable by the normal conjugal process. However, when R(21)(TC)(+) transductants are infected with the F(13) factor, the nontransferable R(21)(TC) factor acquires transmissibility by conjugation. R(21)(TC)(+) conjugants of Escherichia coli K-12, to which only the R(21)(TC) factor was transmitted by cell-to-cell contact from an F' R(+) donor, were still unable to transfer their R(21)(TC) factor by conjugation. In crosses between Hfr and F(-)E. coli K-12 strains containing R(21)(TC), the gene responsible for tetracycline resistance was located on the E. coli K-12 chromosome between lac and pro, near lac.