Abortive infection by bacteriophage BF23 due to the colicin Ib factor. II. Involvement of pre-early proteins

T5-like phage BF23 evades host-mediated DNA restriction and methylation

Bacteriophage BF23 is a close relative of phage T5, a prototypical Tequintavirus that infects Escherichia coli. BF23 was isolated in the middle of the XXth century and was extensively studied as a model object. Like T5, BF23 carries long ∼9.7 kb terminal repeats, injects its genome into infected cell in a two-stage process, and carries multiple specific nicks in its double-stranded genomic DNA. The two phages rely on different host secondary receptors-FhuA (T5) and BtuB (BF23). Only short fragments of the BF23 genome, including the region encoding receptor interacting proteins, have been determined. Here, we report the full genomic sequence of BF23 and describe the protein content of its virion. T5-like phages represent a unique group that resist restriction by most nuclease-based host immunity systems. We show that BF23, like other Tequintavirus phages, resist Types I/II/III restriction-modification host immunity systems if their recognition sites are located outside the terminal repeats. We also demonstrate that the BF23 avoids host-mediated methylation. We propose that inhibition of methylation is a common feature of Tequintavirus and Epseptimavirus genera phages, that is not, however, associated with their antirestriction activity.

Identity of genes A2 and A3 of bacteriophage BF23

The polypeptide coded by gene A3 of bacteriophage BF23 has been purified and its N-terminal amino acid sequence determined. This sequence is identical to the N-terminal sequence of the polypeptide coded by gene A2. The two gene products have identical molecular weight. We conclude that these two gene products are identical, and are coded by one and the same gene, namely gene A2-A3, which was previously thought to be two genes, A2 and A3.

Regulation of the temporal synthesis of proteins in bacteriophage BF23-infected cells

Regulation of temporal synthesis of pre-early, early, and late proteins in bacteriophage BF23-infected cells has been studied by using five amber mutants defective in genes 1, 2, 10, 14, and 19. The synthesis of pre-early proteins is negatively regulated by the actions of gene 1, a pre-early gene. The switch from pre-early to early protein synthesis is mainly regulated by the second-step DNA transfer reaction, which is controlled by at least genes 1 and 2. Early proteins can be kinetically and genetically divided into two regulatory classes, designated Ea and Eb. The shutoff of Eb-early protein synthesis is associated with the turn-on of late protein synthesis. This step is controlled by genes 10, 14, and 19. Gene 10 also regulates negatively the synthesis of Ea-early proteins, indicating that this gene has a dual function in the regulation of early protein synthesis. The temporal synthesis of phage-encoded proteins is regulated mainly at the transcriptional level. Evidence is presented indicating that the host RNA polymerase is modified by the interaction with the gene products of genes 2, 10, and 14 (gp2, gp10, and gp14, respectively). gp2 interacts with the enzyme in the earlier stage of infection but is replaced by gp10 in the later stage. This exchange reaction depends on the presence of gp14 and gp19 and is related to the switch from Eb to late protein synthesis. Thus, the regulation of BF23 gene expression occurs in a coordinated manner throughout the development of this phage.

Growth of coliphage BF23 on rough strains of Salmonella typhimurium: the bfe locus

Coliphage BF23 develops in Salmonella typhimurium rough strains. The phage is neither restricted nor modified by S. typhimurium. The growth patterns of the phage were slightly different in S. typhimurium than in Escherichia coli, although phage propagated on S. typhimurium is identical to the phage propagated in E. coli by several criteria used. Mutants of S. typhimurium resistant to BF23 were isolated and found to map (by P22- and Pl-mediated transduction) in the same position as bfe mutants of E. coli. The order of genes was: metB - argC - bfe - rif - purD - metA. Phage BF23 does not form plaques on smooth S. typhimurium strains, since the phage fails to adsorb irreversibly to smooth cells. Nevertheless, on solid agar, the phage prevents growth of many (but not all) smooth strains. Moreover, UV- and alkali-inactivated phage BF23, although unable to form plaques on sensitive hosts, retains the ability to prevent growth of the host on solid medium. This ability is sensitive to protease and resistant to DNAse and RNase. Heat treatment of the phage causes rapid loss of the cell-growth-preventing-ability whereas the ability to form plaques is lost much more slowly. These results lead to a proposal that phage BF23 virions carry a colicin-like factor that kills sensitive cells.

Membrane protein biosynthesis in bacteriophage BF23-infected Escherichia coli

When Escherichia coli is infected with bacteriophage BF23, two new proteins with molecular weights greater than 10,000, as indicated by polyacrylamide gel electrophoresis, are found associated with the cells' membranes. One of these, found associated with both the inner and outer membrane, has a molecular weight of about 55,000 and is regulated by the A1 gene of this phage, a gene found on the spontaneously injected 8% piece of BF23 DNA, DNA that codes for the synthesis of proteins necessary for the injection of the whole phage genome. The other protein, often undetected in whole membrane preparations, is found exclusively associated with the inner membrane. Evidence indicates that this protein is also regulated by the initially injected 8% piece of the DNA.

Isolation and genetic characterizaion of Escherichia coli K-12 mutations affecting bacteriophage T5 restriction by the ColIb plasmid

A mutant derivative of Escherichia coli K-12 has been isolated which is permissive for bacteriophage T5 infection even when harboring a wild-type ColIb plasmid. The fully permissive phenotype was the result of two mutations that are located near the rpsL-rpsE region on the E. coli chromosome and are recessive to the wild-type alleles. These mutations had little or no effect on induction of colicin synthesis and did not affect the expression of antibiotic resistance by the resistance plasmids R64drd11 or R1drd19. Cells harboring the mutant alleles grew more slowly than isogenic wild-type derivatives in either minimal or complete media.

Identification of the gene controlling the synthesis of the major bacteriophage T5 membrane protein

After infection of Escherichia coli B by bacteriophage T5, a major new protein species, as indicated by polyacrylamide gel electrophoresis, appears in the cells' membranes. Phage mutants with amber mutations in the first-step-transfer portion of their DNA have been tested for their ability to induce membrane protein synthesis after they infect E. coli B. We have found that phage with mutations in the Al gene of T5 do not induce the synthesis of the T5-specific major membrane protein, whereas phage that are mutant in the A2 gene do induce its synthesis. We conclude that gene Al must function normally for T5-specific membrane protein biosynthesis to occur and that only the first 8% (first-step-transfer piece) of the DNA need be present in the cell for synthesis to occur.

The regulation of transcription in bacteriophage T5-infected Escherichia coli

The expression of bacteriophage T5-specific RNA and protein in infected cells is temporally separated into three classes: class I (preearly), class II (early), and class III (late). By immunoprecipitation techniques we have shown that T5 infection of cells leads to the synthesis of one class I polypeptide (11,000 daltons) and two class II polypeptides (90,000 and 15,000 daltons) capable of binding to the RNA polymerase of the host Escherichia coli cell. One of the class II polypeptides (90,000 daltons) is the product of gene C2, which is an essential gene product required for the initiation of class III RNA synthesis. The colicinogenic factor, ColIb, is a plasmid which prevents the normal synthesis of class II and the III bacteriophage T5-specific RNA in infected colicinogenic (ColIb+) cells. In T5-infected colicinogenic cells, only the T5 class I polypeptide is found associated with the RNA polymerase. Mutants of T5, designated T5h minus, are capable of growth on both noncolicinogenic and ColIb+ hosts. Extracts of T5h minus infected ColIb+ cells were shown to lack a small class I polypeptide (12,000 daltons) as compared to T5-infected cells. The h minus mutation, however, has no effect on the levels of the class I T5 polypeptide of similar molecular weight which is bound to the RNA polymerase. One effect of the h minus mutation is to enhance the quantities of the two class II polypeptides bound to the enzyme.