The Deoxyribonuclease of Typhoid Bacilli and its Effect on Typhoid Bacteriophage Nucleic Acid

Abstract

SUMMARY: Deoxyribonuclease (DNase) was found in extracts of a strain of Salmonella typhi. Its action on herring sperm deoxyribonucleic acid (DNA) is catalysed by magnesium ions. Calcium ions, although inactive alone, increase the magnesium-catalysed activity of the enzyme. A highly polymerized specimen of phage DNA was prepared by treatment of the purified phage with strong urea solution to dissolve the protein coat. This nucleic acid is degraded by the typhoid DNase in the presence of magnesium. As with herring sperm DNA, calcium is inactive alone but increases the action of magnesium. Calcium is required for multiplication of the phage in the host bacterium, but the hypothesis that the calcium is required to catalyse the breakdown of phage DNA by bacterial DNase was not upheld.