GENOMIC CLEAVAGE MAP OF SALMONELLA-TYPHI TY2

The genomic cleavage map of Salmonella typhi Ty2, 4,780 kb in size, wa s determined through digestion of the genomic DNA with endonucleases a nd separation of the fragments by pulsed-field gel electrophoresis. Th e chromosome has 33, 26, 7, and 35 sites for the enzymes XbaI, BlnI, I -CeuI, and SpeI, respectively. The fragments were arranged around the chromosome through excision of fragments from the gel, redigestion wit h a second enzyme, end labelling with P-32, and reelectrophoresis and named in alphabetical order. Tn10 transposons inserted in 82 different genes of Salmonella typhimurium were transduced by phage P22 into S. typhi, and the location of Tn10, and thus of the gene, was mapped thro ugh the XbaI and BlnI sites of Tn10. All seven I-CeuI sites (in rrl ge nes for 23S rRNA) were conserved, and the gene order within the I-CeuI fragments resembles that of S. typhimurium LT2, but the order of I-Ce uI fragments is rearranged from ABCDEFG in S. typhimurium LT2 to AGCEF DB in S. typhi. In addition, there is a 500-kb inversion which covers the terminus region. Comparisons of lengths of segments between genes showed that S. typhi has segments which differ in size from those in S . typhimurium. The viaB locus, for synthesis of the Vi antigen of S. t yphi, was shown to be within a 118-kb loop (a segment of DNA with no h omolog in most other Salmonella species) between mel and poxA on the c hromosome.