Inhibitory effect of bacteriophage P22 infection on host cell deoxyribonuclease activity

Infection of Salmonella typhimurium with phage P22 causes a decrease in the activity of host deoxyribonuclease which degrades single-stranded deoxyribonucleic acid (DNA). This decrease is reversed when the infecting phage is P22c(+); it is not reversed if the infecting phage kills the cell. The decrease does not occur in infections with P22ts25.1 (which only adsorbs and injects DNA) or in infections of a lysogen by a nonvirulent phage. It does occur, however, after infections with other phages which are blocked in phage DNA synthesis. Inhibiting protein synthesis with chloramphenicol does not in itself cause the decrease in uninfected cells, but it does prevent infected cells from showing this effect.