Genetic mapping of IS200 copies in Salmonella typhimurim strain LT2

The wild-type Salmonella typhimurium strain LT2 contains six copies of the insertion sequence element IS200 which is unique to Salmonella. We have determined the chromosomal locations of all six copies of IS200 in strain LT2. This was done by mapping the positions of Tn10 elements inserted near each copy of IS200. Such Tn10 insertions were detected by Southern hybridization as IS200-containing restriction fragments with altered electrophoretic mobility. The copies are located at quite evenly spaced sites in the chromosome. Some are found in regions with many known genes; others are in regions with few known functions. There is no indication of a possible function for IS200. The method described here should be applicable to the mapping of IS elements in general.