Copyright ©) 1993, American Society for Microbiology Location of IS200 on the Genomic Cleavage Map of

Locations of six TnlOs, closely linked to each of the six IS200s on the genomic cleavage map of Salmonella typhimurium LT2, were determined by digestion with XbaI and BlnI and separation of the fragments by pulsed-field gel electrophoresis; the locations were then further defined by P22-mediated joint transduction. The orientation of each IS200 with respect to its linked TnlO was determined by Southern blotting. The locations of IS200-I, IS200-III, and IS200-V were confirmed to be close to sujD, meiB, and purC, as previously indicated. IS200-II is jointly transduced with cysG. IS200-IV is near fliA; the linked TnlO is inserted in fli, making the strain nonmotile. IS200-VI is jointly transduced with aspC but not with aroA. IS200 is transposed to a seventh site in some strains, while remaining in the other six locations described above. These data indicate that genome analysis by pulsed-field gel electrophoresis can locate the positions of TnlOs with accuracy sufficient to predict P22-mediated joint transduction. Salmonella typhimurium LT2 contains six copies of the insertion sequence IS200 (9, 10). IS200 is 708 bp in length and is thus the smallest known bacterial insertion sequence (4-6, 11). The structure of the chromosome and the order of genes i