Arrest of host DNA synthesis in Bacillus subtilis infected with phage phi e

Bacteriophages of Bacillus subtilis

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Bacillus subtilis DNA polymerase III is required for the replication of the virulent bacteriophage phi e

The virulent phage phie of Bacillus subtilis which contains hydroxymethyluracil in its DNA requires host DNA polymerase III for its DNA replication. DNA polymerase III(ts) mutant cells infected with phie at restrictive temperatures do not support phage DNA synthesis. However, phie grows normally both at low and high temperatures in the mutant's parent strain and in spontaneous DNA polymerase III(+) revertants isolated from the mutant strain. Temperature-shift-down experiments with phie-infected cells having thermosensitive DNA polymerase III (pol III(ts)) indicate that at 48 C the thermolabile DNA polymerase III is irreversibly inactivated and has to be synthesized de novo after the shift to 37 C, before phage DNA synthesis can begin. Temperature-shift-up experiments with phie-infected mutant cells show that phage replication is arrested immediately after the temperature shift and indicate that phie requires DNA polymerase III throughout its replication stage.

Mutants of Bacillus subtilis bacteriophage phi e defective in dTTP-dUTP nucleotidohydrolase

Mutants of bacteriophage phie inducing only 1 to 5% of wild-type levels of dTTP-dUTP nucleotidohydrolase give normal bursts of viable progeny phage whose DNA contains 5 to 10% thymine (but no uracil) in place of 5-hydroxymethyluracil. The relative heat lability of one phage mutant enzyme solubilized from the membrane fraction of infected cells suggests that a phie gene codes for the induced dTTPase-dUTPase.

Synthesis of bacteriophage and host DNA in toluene-treated cells prepared from T4-infected Escherichia coli: role of bacteriophage gene D2a

We investigated the synthesis of DNA in toluene-treated cells prepared from Escherichia coli infected with bacteriophage T4. If the phage carry certain rII deletion mutations, those which extend into the nearby D2a region, the following results are obtained: (i) phage DNA synthesis occurs unless the phage carries certain DNA-negative mutations; and (ii) host DNA synthesis occurs even though the phage infection has already resulted in the cessation of host DNA synthesis in vivo. The latter result indicates that the phage-induced cessation of host DNA synthesis is not due to an irreversible inactivation of an essential component of the replication apparatus. If the phage are D2a(+), host DNA synthesis in toluene-treated infected cells is markedly reduced; phage DNA synthesis is probably also reduced somewhat. These D2a effects, considered along with our earlier work, suggest that a D2a-controlled nuclease, specific for cytosine-containing DNA, is active in toluene-treated cells.