Shutoff of Host RNA Synthesis in Bacteriophage T4-Infected Escherichia coli in the Absence of Host DNA Degradation and Nuclear Disruption
Journal of Virology
In contrast to its effect on host DNA synthesis, nuclear disruption in phage T4-infected Escherichia coli B/5 cells has no effect on the shutoff of host RNA synthesis. Host RNA synthesis is shut off normally after infection with T4 multiple mutants that fail to induce both nuclear disruption and host DNA degradation. The infection ofEscherichia coli cells with T4 phage results in the rapid arrest of most, if not all, host macromolecular synthesis (see the review by Duckworth ). Host DNA and
... rotein synthesis are shut off normally in cells infected with mutants that fail to induce host DNA degradation (H. Warner, unpublished data; 14). In the absence of nuclear disruption, however, the shutoff of host DNA synthesis is delayed until about 10 min after infection (14) . It was thus of interest to determine whether the absence of nuclear disruption had a similar effect on the shutoff of host RNA synthesis. We used DNA-RNA hybridization of RNA pulse-labeled with [3H]uridine to examine the switch from host RNA synthesis to phage RNA synthesis in cells infected with multiple mutants of phage T4 which are deficient in both host DNA degradation and nuclear disruption (13, 15). The approach used was to pulse label RNA in uninfected E. coli B/5 cells and B/5 cells infected with various T4 phage strains for 3 min (at various times after infection in phageinfected cells), to extract total RNA and remove DNA with RNase-free pancreatic DNase, and to hybridize this RNA to purified T4 and E. coli DNA. A summary of the results of hybridization data for cells infected with wild-type T4D, multiple mutants deficient in both host DNA degradation and nuclear disruption, and control strains is shown in Table 1 . These results suggested that the switch from host RNA synthesis to phage RNA synthesis occurred normally in the absence of both host DNA degradation and nuclear disruption. However, the DNA-RNA ratios in the hybridization mixtures were not high enough to avoid saturation in the case of the E. coli DNA, resulting in low hybridization efficiencies. (It should be emphasized that the values presented in the tables are only comparative, not quantitative, since they are not corrected for the differences in hybridization efficiencies obtained with E. coli and T4 RNA.) The experiment was thus repeated for wild-100.