Bacteriophage-induced inhibition of host functions. I. Degradation of Escherichia coli deoxyribonucleic acid after T4 infection.

The kinetics of degradation of bacterial deoxyribonucleic acid (DNA) after infection of Escherichia coli with T4D, ultraviolet-irradiated T4D, and two amber mutants, N122 and N94, was studied by zone sedimentation through linear glycerol gradients. Within 5 min after infection with any of the bacteriophages, breakdown of host genome was evident. The first product was a high-molecular-weight material (50S to 70S) and further degradation appeared to occur in discrete steps. Rapid and extensive breakdown of bacterial DNA was seen after infection with am N122 and T4D. Infection with ultraviolet-irradiated phage or with am N94 resulted in an accumulation of high-molecular-weight material. These results suggest that the observed degradation of host DNA begins early and requires sequential action of several phage-induced endo- as well as exodeoxyribonucleases.