A new Salmonella typhimurium DNA host specificity.

The genetic properties of a new (hspS) host specificity of Salmonella typhimurium were investigated using bacteriophage L. Phage L is a better substrate for s-specific restriction than phage P22. Mutants deficient in s-restriction only were found at the same frequency as mutants deficient in both restriction and modification. Crosses between S. typhimurium Hfr and S. typhimurium For between Escherichia coli and S. typhimurium showed that the s system has the same chromosomal location as the K system of E. coli. The s system was introduced into E. coli and found to be effective on phage A.