Abstract
High-frequency transfer of the chromosomal trp region by [plasmid] R1 observed in E. coli also occurs in S. typhimurium. The reaction is recA independent in both species. The origin of transfer lies within a segment of the chromosome that is inverted in S. typhimurium relative to E. coli, and thus transfer occurs in a different direction in the 2 spp. The character of R1 that is responsible, known as Tfa+, may be lost without affecting other properties of the R factor such as its own transfer.