CTNSCR94, A CONJUGATIVE TRANSPOSON FOUND IN ENTEROBACTERIA

Conjugational transposons are important for horizontal gene transfer i n gram-positive and gram-negative bacteria, but have not been reported yet for enteric bacteria, Salmonella senftenberg 5494-57 has previous ly been shown to transfer by conjugation genes for a sucrose fermentat ion pathway which were located on a DNA element called scr-94. We repo rt here that the corresponding scr genes for a phosphoenolpyruvate-dep endent sucrose:phosphotransferase system and a sucrose metabolic pathw ay are located on a large (ca. 100 kb) conjugative transposon renamed CTnscr94. The self-transmissible element integrates at two specific at tachment sites in a RecA-independent way into the chromosome of Escher ichia coli K-12 strains, One site was identified within pheV the struc tural gene for a tRNA(Phe). Sequencing of both ends of CTnscr94 reveal ed the presence of the 3' part of pheV on one end such that after inte gration of the element, a complete pheV gene is retained, CTnscr94 rep resents, to our knowledge, the first conjugational transposon found in enteric bacteria.