I-CEUI REVEALS CONSERVATION OF THE GENOME OF INDEPENDENT STRAINS OF SALMONELLA-TYPHIMURIUM

The enzyme I-CeuI, encoded by a class I mobile intron inserted in the gene for 23S rRNA in Chlamydomonas eugamatos, cleaves a specific 19-bp sequence in this gene. This sequence is present only in the seven gen es for rRNA in Salmonella typhimurium and Escherichia coli. Partial di gestion with I-CeuI of DNA from 17 wild-type strains of S. typhimurium indicates that the chromosome of these strains is strongly conserved, for the digestion products closely resemble those of strain LT2. The lengths and order of chromosomal segments are conserved in 15 of the s trains; 2 show some rearrangements. XbaI digestion indicated heterogen eity without revealing the genomic structure. Because of conservation of I-CeuI sites in genes for rRNA and conservation of the number and l ocations of these genes, I-CeuI provides an excellent tool for the rap id examination of the chromosomes of related species of bacteria; diff erences in the fingerprints indicate the occurrence of chromosomal rea rrangements such as insertions or inversions.