A BlnI restriction map of the Salmonella typhimurium LT2 genome.

BlnI or AvrII (5'-CCTAGG) sites are very rare in the Salmonella typhimurium LT2 genome. BlnI was used to construct a physical map which was correlated with the genetic map by using three methods. First, Tn10 carries BlnI sites, and the extra restriction sites produced by 34 genetically mapped Tn10 insertions were physically mapped by using pulsed-field gel electrophoresis. Second, six genetically mapped Mud-P22 prophage insertions were used to assign BlnI fragments. Integration of Mud-P22 introduces 30 kb of DNA that can easily be detected by a "shift up" in all but the largest BlnI fragments. Finally, induced Mud-P22 insertions package more than 100 kb of genomic DNA adjacent to one side of the insertion. Some of the smaller BlnI fragments were localized by hybridization to a dot blot array of 52 lysates from induced Mud-P22 insertions. Of the 10 BlnI sites mapped, 6 probably occur in or near the 16S rRNA genes at about 55, 71, 83, 86, 88.5, and 89.5 min. There is one BlnI site in the 90-kb pSLT plasmid. Two additional BlnI fragments of about 7 and 4 kb have not been localized. The size of the genome was estimated as 4.78 Mb (+/- 0.1 Mb) excluding pSLT but including prophages Fels-1 and Fels-2. One BlnI fragment that maps between 55 and 59 min showed a 40-kb reduction in size in a strain cured of the approximately 40-kb Fels-2 prophage.