Immediate-early expression of the gene causing superinfection breakdown in bacteriophage T4B

Selection for bacteriophage latent period length by bacterial density: A theoretical examination

In bacteriophage (phage), rapid and efficient intracellular progeny production is of obvious benefit. A short latent period is not. All else being equal, a longer latent period utilizes host cell resources more completely. Using established parameters of phage growth, a simulation of three successive phage lysis cycles is presented. I have found that high, but not low, host cell densities can select for short phage latent periods. This results from phage with short latent periods more rapidly establishing multiple parallel infections at high host cell concentrations, whereas phage with long latent periods are restricted to growth within a single cell over the same period. This implies that phage with short latent periods habitually grow in environments that are rich in host cells.

The functions of the phage T4 immunity and spackle genes in genetic exclusion

Genetic exclusion is the ability of a primary infecting phage to prevent a secondary infecting phage from contributing its genetic information to the progeny. The molecular mechanism of the phenomenon is not well understood. The two genes in phage T4 mainly responsible for genetic exclusion are the immunity (imm) gene and the spackle (sp) gene. Evidence is presented that the imm gp enables the host exonuclease V to degrade superinfecting phage DNA. This appears to be accomplished by the imm gp altering gp 2/64, the presumed pilot protein, which protects the 5′ end(s) of the phage DNA. Exonuclease III is also involved in genetic exclusion but its action does not appear to depend upon theimmorspgene products. Gp sp appears to interfere with the lysozyme activity of gp 5, a component of the central base plug, postulated to aid in tail tube penetration during the injection process. A molecular model of genetic exclusion is proposed. Genesimmandspare part of a cluster of genes which also includes42, beta-glucosyltransferase, anduvsX. The genes of this cluster encode proteins apparently adapted for competition and defence at the DNA level. These genes may encode fundamental adaptive strategies found throughout nature.

Recovery of the accumulation ability of thiomethyl-beta-galactoside in Escherichia coli after bacteriophage T4 infection

Effects of UV-irridiated and unirradiated T4 phage infection on the beta-galactoside accumulation ability in Eschericia coli have been examined by the use of 14C-labeled thiomethyl-beta-galactoside (TMG). Under conditions where a synchronous adsorption of phage takes place, the cellular ability for TMG accumulation is found to be largely inhibited immediately after phage adsorption, but it recovers with time to a new level, which is dependent on the multiplicity of infection. When cells are infected with UV-irradiated T4 at the same multiplicity as that of unirradiated phage, the cellular accumulation ability is more severely inhibited and there is no recovery from the inhibition. The recovery process in T4-infected cells is mostly sensitive to puromycin. These results suggest that the initial inhibition of the TMG accumulation ability is probably caused by the adsorption of phage coats, and the subsequent restoration occurs through the action of a phage-directed protein(s). In the recovery process, no new transport system appears to be involved. The restored ability of TMG accumulation is resistant to the action of superinfecting UV phage. However, different mechanisms appear to be operating in T4-infected cells for the establishment of resistance to ghosts and for the recovery from the phage coat-induced inhibition.