Establishment of repression by bacteriophage lambda: lack of a direct regulatory effect of cyclic AMP

Control of phage lambda development by stability and synthesis of cII protein: role of the viral cIII and host hflA, himA and himD genes

The cII protein of bacteriophage lambda has a decisive role in the regulatory switch between the lysogenic and lytic pathways of viral development. Recent work has indicated that cII may be the primary control function providing for the initial partition between the two pathways, with other host and viral regulatory genes acting to determine the levels of cII in an infected cell. We have studied the synthesis and stability of cII protein with two experimental systems, phage infection and a cII-producing plasmid. We have found that the stability of cII is controlled by the host hflA and viral cIII genes; hflA protein facilitates degradation of cII, whereas cIII protects cII. The synthesis of cII appears to be under the positive control of the host himA and himD genes. We conclude that posttranscriptional regulation of cII by host and viral genes is critical for the choice of a developmental pathway.

Control of cI gene expression in bacteriophage lambda imm434, studied in an immunity/trp fusion made in vitro

The trp genes of a lambda imm434 trp-transducing phage have been fused to the immunity region by deletion, in vitro, of the DNA between two targets for the restriction enzyme R.EcoRI. The resulting phage has been used to study the control of expression of the cI gene in vivo. The constitutive rate of expression of the cI gene is between 2 and 5% of the maximally stimulated rate. The products of the cII and cIII genes enhance expression of cI on infection of a sensitive host. The requirement for the cII product is more stringent than that for the cIII protein. The phage 434 repressor present in a 434-immune cell stimulates the rate of cI expression from a superinfecting homoimmune phage about fifteen-fold. This result strongly suggests that repressor stimulates its own synthesis by a direct effect on transcription of the cI gene.

Mutant of Salmonella typhimurium that channels infecting bacteriophage P22 toward lysogenization

A slowly growing, polymyxin-sensitive mutant of Salmonella typhimurium was isolated. Wild-type phage P22 form plaques on the mutant at 5 x 10(-4), the frequency observed on wild-type hosts. All P22 clear mutants form plaques with near normal frequency. The inability of the mutant to form plaques is correlated with an increase in lysogenization frequency. The cause of the increased lysogenization frequency is not known, but it is not the result of overproduction of cyclic adenosine 5'-monophosphate.

The roles of the lambda c3 gene and the Escherichia coli catabolite gene activation system in the establishment of lysogeny by bacteriophage lambda

Maximum lysogenization of E. coli by bacteriophage lambda requires both the lambdacIII gene function and the host catabolite gene activation system mediated by adenosine 3':5'-cyclic monophosphate. Whereas considerable lysogenization occurs in the presence of either system alone, lysogenization is absolutely prevented in the absence of both systems. Neither system is, however, required for efficient lysogenization when the host bears an hfl(-) mutation. It is argued that the normal function of these two systems is to negate the antagonistic effect of the Hfl(+) protein upon lysogenization. It is further argued that both the lambdacIII gene function and the Hfl(+) protein do not directly affect the host catabolite gene activation system.