fii, a bacterial locus required for filamentous phage infection and its relation to colicin-tolerant tolA and tolB.

We describe mutations in a new bacterial locus, designated fii, which do not allow the filamentous bacteriophage f1 to infect bacteria harboring the F plasmid. Mutations at this locus do not affect the ability of F plasmid-containing bacteria to undergo conjugation or be infected by the F plasmid-specific RNA phage f2. The filamentous phage can still adsorb to the F sex pilus, but the DNA is unable to enter the bacteria. All fii mutants become tolerant to colicins E1, E2, and E3. Strains with amber mutations in fii also are unable to plaque P1, even though they can be infected with this phage. Mutations in fii also prevent infection of bacteria harboring the N plasmid by the filamentous bacteriophage IKe. The fii locus maps adjacent to tolA, mutants of which demonstrate tolerance to high levels of the E and K colicins. The three genes tolA, tolB, and fii are shown to reside on a 4.3-kilobase fragment of the Escherichia coli chromosome. Each gene has been cloned into a chimeric plasmid and shown to complement, in trans, mutations at the corresponding chromosomal locus. Studies in maxicells show that the product of fii appears to be a 24-kilodalton protein which copurifies with the cell envelope. The product of tolA has been identified tentatively as a 51-kilodalton protein. Data from cloning, Tn5 mutagenesis, and P1 transduction studies are consistent with the gene order sucA-fii-tolA-tolB-aroG near 17 min on the E. coli map.     

Growth and DNA synthesis of bacteriophage phi x174 in a dnaP mutant of Escherichia coli.

phi X174am3trD, a temperature-resistant mutant of bacteriophage phi X174am3, exhibited a reduced ability to grow in a dnaP mutant, Escherichia coli KM107, at the restrictive temperature (43 degrees C). Under conditions at which the dnaP gene function was inactivated, the amount and the rate of phi X174am3trD DNA synthesis were reduced. The efficiency of phage attachment to E. coli KM107 at 43 degrees C was the same as to the parental strain, E. coli KD4301, but phage eclipse and phage DNA penetration were inhibited in E. coli KM107 at 43 degrees C. It is suggested that the dnaP gene product, which is necessary for the initiation of host DNA replication, participates in the conversion of attached phages to eclipsed particles and in phage DNA penetration in vivo in normal infection.     

Nucleotide sequence of a gene cluster involved in entry of E colicins and single-stranded DNA of infecting filamentous bacteriophages into Escherichia coli.

Mutations in fii or tolA of the fii-tolA-tolB gene cluster at 17 min on the Escherichia coli map render cells tolerant to high concentrations of the E colicins and do not allow the DNA of infecting single-stranded filamentous bacteriophages to enter the bacterial cytoplasm. The nucleotide sequence of a 1,854-base-pair DNA fragment carrying the fii region was determined. This sequence predicts three open reading frames sequentially coding for proteins of 134, 230, and 142 amino acids, followed by the potential start of the tolA gene. Oligonucleotide mutagenesis of each open reading frame and maxicell analysis demonstrated that all open reading frames are expressed in vivo. Sequence analysis of mutant fii genes identified the 230-amino acid protein as the fii gene product. Chromosomal insertion mutations were constructed in each of the two remaining open reading frames. The phenotype resulting from an insertion of the chloramphenicol gene into the gene coding for the 142-amino acid protein is identical to that of mutations in fii and tolA. This gene is located between fii and tolA, and we propose the designation of tolQRA for this cluster in which tolQ is the former fii gene and tolR is the new open reading frame. The protein products of this gene cluster play an important role in the transport of large molecules such as the E colicins and filamentous phage DNA into the bacterium.     

Rescue of abortive T7 gene 2 mutant phage infection by rifampin.

Infection of Escherichia coli with T7 gene 2 mutant phage was abortive; concatemeric phage DNA was synthesized but was not packaged into the phage head, resulting in an accumulation of DNA species shorter in size than the phage genome, concomitant with an accumulation of phage head-related structures. Appearance of concatemeric T7 DNA in gene 2 mutant phage infection during onset of T7 DNA replication indicates that the product of gene 2 was required for proper processing or packaging of concatemer DNA rather than for the synthesis of T7 progeny DNA or concatemer formation. This abortive infection by gene 2 mutant phage could be rescued by rifampin. If rifampin was added at the onset of T7 DNA replication, concatemeric DNA molecules were properly packaged into phage heads, as evidenced by the production of infectious progeny phage. Since the gene 2 product acts as a specific inhibitor of E. coli RNA polymerase by preventing the enzyme from binding T7 DNA, uninhibited E. coli RNA polymerase in gene 2 mutant phage-infected cells interacts with concatemeric T7 DNA and perturbs proper DNA processing unless another inhibitor of the enzyme (rifampin) was added. Therefore, the involvement of gene 2 protein in T7 DNA processing may be due to its single function as the specific inhibitor of the host E. coli RNA polymerase.     

Genetics and physiology of colicin-tolerant mutants of Escherichia coli

A series of colicin-tolerant (tol) mutants of Escherichia coli K-12, which adsorbed colicins but were not killed by them, were isolated and studied genetically and physiologically. Three major classes of mutants were found: tol II, tolerant to colicins A, E1, E2, E3, and K; tol III, tolerant to A, E2, E3, and K; and tol VIII, tolerant to E1 only. The sites of tol II and tol III mutations mapped near the gal region (gene order: tol-gal-bio) and were cotransduced with gal by P1. In heterozygous diploids, tol(+) was dominant over tol; tol II and tol III gave full complementation. All the tol mutations that mapped near gal rendered the bacteria more fragile during growth and hypersensitive to deoxycholate and to ethylenediaminetetraacetic acid. The tol VIII mutation mapped between str and his. These mutants were extremely sensitive to deoxycholate and were also hypersensitive to methylene blue, acridines, and various other compounds. The sensitivity is attributed to increased uptake due to selective alteration of the permeability barrier. The colicin-tolerant mutations are interpreted as affecting some components of the cytoplasmic membrane which mediate between the adsorbed colicin molecules and the target sites of their biochemical effects in the bacterial cell.     

Lysis gene t of T-even bacteriophages: evidence that colicins and bacteriophage genes have common ancestors.

The lysis gene t of the T-even-like bacteriophage K3 has been cloned and sequenced. The gene codes for a protein with a predicted molecular weight of 25,200. Expression of the complete lysis protein was impossible, but peptides complementing T4 amber mutants in t are described. No known lysis protein of other phages is homologous to protein T. Also, the Escherichia coli phospholipase A is different from protein T. CelB, the lysis protein of the colicin E2 operon, shows a similarity to protein T. Sequences of colicins A, E1, and E2 are related to gene 38 sequences, the gene preceding t and coding for the phage adhesin. A common origin for colicin genes and phage genes is discussed, and a protein region in colicins that is responsible for receptor recognition is predicted.     

Genetics of colicin E susceptibility inCitrobacter freundii

The insensitivity ofCitrobacter freundii to the E colicins is based on tolerance to colicin E1 and resistance to colicins E2 and E3. Spontaneous colicin A resistant mutants ofC. freundii also lost their colicin E1 receptor function. Sensitivity to colicin E1 can be induced by F′gal ⁺ tol ⁺ plasmids, thetol A⁺ gene product of which is responsible for this effect. Receptor function for colicins E2 and E3 is induced by theE. coli F′14bfe ⁺ plasmid, which is also able to enhance notably the receptor capacity for colicin E1. Thebfe ⁺ gene product ofE. coli, which is responsible for these phenomena, also restores the receptor function for colicin A and E1 in colicin A resistant mutants ofC. freundii. All results show that there is a remarkable difference between theE. coli bfe ⁺ gene product and thebfe ⁺ gene product ofC. freundii and also between thetol A⁺ gene products of these strains. The sensitivity to phage BF23 parallels the sensitivity to colicins E2 and E3 and is also induced by the F′14bfe ⁺ plasmid.     

The effect of supercoiling of DNA from colicinogenic plasmids on the expression of col, imm and lys genes

The expression of colicin genes is controlled by the SOS-system (Lex A repressor) and the adenylate-cyclase system (cAMP-CAP complex). The effect of plasmid DNA supercoiling on the expression of the operons of colicins E1, E2, and E3 has been studied by using E. coli minicells. It has been shown for the colicin E1 operon that it is the promoter that is influenced by supercoiling: an increase in negative supercoiling elevates the expression and, vice versa, DNA relaxation reduces the expression. The effect of supercoiling on gene activity of the colicin E1 immunity protein has not been observed, which may be due to the specific orientation of this gene. With the two other colicins supercoiling affects the expression of all genes which constitute the operon. The regulation of the colicin operon expression has been confirmed to occur at three levels: by the LexA protein, by the cAMP-CAP complex, and by the plasmid DNA supercoiling.     

Genes affecting coliphage BF23 and E colicin sensitivity in Salmonella typhimurium.

Rough strains of Salmonella typhimurium were sensitive to coliphage BF23. Spontaneous mutants resistant to BF23 (bfe) were isolated, and the trait was mapped using phage P1. The bfe gene in S. typhimurium was located between argF (66% co-transducible) and rif (61% co-transducible). The BF23-sensitive S. typhimurium strains were not sensitive to the E colicins. Cells of these rough strains absorbed colicin, as measured by loss of E2 or E3 killing units from colicin solutions and by specific adsorption of 125I-colicin E2 to bfe+ cells. Sensitivity to colicins E1, E2, and E3 was observed in a S. typhimurium strain carrying the F'8 gal+ episome. This episome complemented the tolB mutation of Escherichia coli. We conclude that the bfe+ protein satisfies requirements for adsorption of both phage BF23 and the E colicins. In addition, expression of a gene from E. coli, possibly tolB, is necessary for efficient E colicin killing of S. typhimurium.     

A hybrid toxin from bacteriophage f1 attachment protein and colicin E3 has altered cell receptor specificity.

A hybrid protein was constructed in vitro which consists of the first 372 amino acids of the attachment (gene III) protein of filamentous bacteriophage f1 fused, in frame, to the carboxy-terminal catalytic domain of colicin E3. The hybrid toxin killed cells that had the F-pilus receptor for phage f1 but not F- cells. The activity of the hybrid protein was not dependent upon the presence of the colicin E3 receptor, BtuB protein. The killing activity was colicin E3 specific, since F+ cells expressing the colicin E3 immunity gene were not killed. Entry of the hybrid toxin was also shown to depend on the products of tolA, tolQ, and tolR which are required both for phage f1 infection and for entry of E colicins. TolB protein, which is required for killing by colicin E3, but not for infection by phage f1, was also found to be necessary for the killing activity of the hybrid toxin. The gene III protein-colicin E3 hybrid was released from producing cells into the culture medium, although the colicin E3 lysis protein was not present in those cells. The secretion was shown to depend on the 18-amino-acid-long gene III protein signal sequence. Deletion of amino acids 3 to 18 of the gene III moiety of the hybrid protein resulted in active toxin, which remained inside producing cells unless it was mechanically released.     

Functional stability of the bfe and tonB gene products in Escherichia coli.

The expression of several functional properties of the products of the bfe and tonB genes in Escherichia coli was measured after the specific termination of the synthesis of the products of these genes. This was accomplished by the use of a temperature-sensitive amber suppressor mutation, which allowed control, by manipulation of the growth temperature, of the level of product formed from suppressible mutant alleles of the bfe or tonB gene. The bfe product is an outer membrane receptor protein for vitamin B12, the E-colicins, and bacteriophage BF23. The identity of the tonB product is unknown, but it is necessary for a subsequent step of uptake of vitamin B12, iron chelates, all of the group B colicins, and bacteriophages T1 and phi 80. Results from a different experimental system had shown that the termination of expression of the bfe locus was rapidly followed by loss of sensitivity to colicins E2 and E3 and, subsequently, to bacteriophage BF23. This was confirmed with this experimental system. Receptors that were no longer functional for colicin or phage uptake remained fully effective for B12 uptake, showing that receptors are stable on the cell surface. This supports previous contentions for the presence of different functional states for colicin receptors. The functional properties of the tonB product, measured by B12 uptake or sensitivity to the group B colicin D, were unstable, declining extensively after cessation of its synthesis.     

Binding of mammalian ribosomes to MS2 phage RNA reveals an overlapping gene encoding a lysis function.

The main binding site for mammalian ribosomes on the single-stranded RNA of bacteriophage MS2 is located nine tenths of the way through the coat protein gene. Translation initiated at an AUG triplet in the +1 frame yields a 75 amino acid polypeptide which terminates within the synthetase gene at a UAA codon, also in the +1 frame. Partial amino acid sequence analysis of the product synthesized in relatively large amounts by mammalian ribosomes confirms this assignment of the overlapping cistron. The same protein is made in an E. coli cell-free system, but only in very small amounts. Analysis of the translation products directed by RNA from op3, a UGA nonsense mutant of phage f2, identifies the overlapping cistron as a lysis gene. In this paper we show that the op3 mutation is a C yield U transition occurring in the second codon of the synthetase cistron, which explains the lowered production of phage replicase (as well as lack of lysis) upon op3 infection of nonpermissive cells. We discuss the properties of the overlapping gene in relation to its lysis function, recognition of the lysis initiator region by E. coli versus eucaryotic ribosomes and op3 as a ribosome binding site mutant for the f2 synthetase cistron.     

DNA sequence analysis of the Serratia marcescens ompA gene: implications for the organisation of an enterobacterial outer membrane protein

Summary The cloned ompA gene from Serratia marcescens was fully expressed in Escherichia coli and its product correctly assembled into the outer membrane. The S. marcescens polypeptide was not functionally equivalent to the E. coli OmpA protein, which serves as a phage receptor and as a component of several colincin uptake systems. DNA sequence analysis of the gene showed that three regions of the protein likely to be exposed on the cell surface not only differed extensively from the corresponding regions of the E. coli polypeptide but also from all other sequenced OmpA proteins. It is suggested that this sequence polymorphism represents a safety mechanism by which the various enterobacterial species can avoid cross-infection by noxious agents such as phages or colicins.     

Inhibition of Bacteriophage φX174 DNA Replication in dnaB Mutants of Escherichia coli C

Bacteriophage phiX174 DNA replication was examined in temperature-sensitive dnaB mutants of Escherichia coli C to determine which stages require the participation of the product of this host gene. The conversion of the infecting phage single-stranded DNA to the double-stranded replicative form (parental RF synthesis) is completely inhibited at the nonpermissive temperature (41 C) in two of the three dnaB mutants tested. The efficiency of phage eclipse and of phage DNA penetration of these mutant host cells at 41 C is the same as that of the parent host strain. The defect is most likely in the synthesis of the complementary strand DNA. The semiconservative replication of the double-stranded replicative form DNA (RF replication) is inhibited in all three host mutants after shifting from 30 to 41 C. Late in infection, the rate of progeny single-stranded phage DNA synthesis increases following shifts from 30 to 41 C. Approximately the same amounts of phage DNA and of infectious phage particles are made following the shift to 41 C as in the control left at 30 C. The simplest interpretation of our data is that the product of the host dnaB gene is required for phiX174 parental RF synthesis and RF replication, but is not directly involved in phage single-stranded DNA synthesis once it has begun. The possible significance of the synthesis of parental RF DNA at 41 C in one of the three mutants is discussed.     

Isolation and Properties of Escherichia coli Mutants Which Are Nonpermissive for the Growth of Phage Lambda

By selecting survivors of λ phage infection, mutants of Escherichia coli K12 that block reproduction cycle of the phage have been isolated. Fourteen of these phage-tolerant mutants (lam mutants) were chosen and characterized biochemically and genetically. It was shown that these mutants were tolerant to infection by all the lambdoid phages, except for few cases, but they were susceptible to infection by a non-lambdoid temperate phage (φ299), P1 or T phages. The mutants can be divided into at least three groups: (1) A mutant (lam 16) strain that seems to block normal penetration of phage DNA: (2) Three mutant (lam 64, lam 67 and lam 71) strains that block an “early” step(s) of phage growth, including phage DNA synthesis: (3) Six mutant (lam 24, lam 25, lam 26, lam 27, lam 646 and lam 6) strains that block normal functioning of the gene E products and produce unusual head structures. Some lambdoid phages and λ mutants that overcome the interference by the lam mutations have been obtained, and were used as tools for characterizing the host mutations. Two (lam 12 and lam 13) mutant strains and one (lam 1) mutant were inferred as affecting the expression of “late” genes, and early gene, respectively, by this test.     

Bacteriophage T4 Inhibits Colicin E2-Induced Degradation of Escherichia coli Deoxyribonucleic Acid I. Protein Synthesis-Dependent Inhibition

The deoxyribonucleic acid (DNA) of Escherichia coli B is converted by colicin E2 to products soluble in cold trichloroacetic acid; we show that this DNA degradation (hereafter termed solubilization) is subject to inhibition by infection with bacteriophage T4. At least two modes of inhibition may be differentiated on the basis of their sensitivity to chloramphenicol. The following observations on the inhibition of E2 by phage T4 in the absence of chloramphenicol are described: (i) Simultaneous addition to E. coli B of E2 and a phage mutated in genes 42, 46, and 47 results in a virtually complete block of the DNA solubilization normally induced by E2; the mutation in gene 42 prevents phage DNA synthesis, and the mutations in genes 46 and 47 block a late stage of phage-induced solubilization of host DNA. (ii) This triple mutant inhibits equally well when added at any time during the E2-induced solubilization. (iii) Simultaneous addition to E. coli B of E2 and a phage mutated only in gene 42 results in extensive DNA solubilization, but the amount of residual acid-insoluble DNA (20 to 25%) is more characteristic of phage infection than of E2 addition (5% or less). (iv) denA mutants of phage T4 are blocked in an early stage (endonuclease II) of degradation of host DNA; when E2 and a phage mutated in both genes 42 and denA are added to E. coli B, extensive solubilization of DNA occurs with a pattern identical to that observed upon simultaneous addition of E2 and the gene 42 mutant. (v) However, delaying E2 addition for 10 min after infection by this double mutant allows the phage to develop considerable inhibition of E2. (vi) Adsorption of E2 to E. coli B is not impaired by infection with phage mutated in genes 42, 46, and 47. In the presence of chloramphenicol, the inhibition of E2 by the triple-mutant (genes 42, 46, and 47) still occurs, but to a lesser extent.     

Outer Membrane-Dependent Transport Systems in Escherichia coli: Effect of Repression or Cessation of Colicin Receptor Synthesis on Colicin Receptor Activities

Proteins in the outer membrane of gram-negative bacteria serve as general porins or as receptors for specific nutrient transport systems. Many of these proteins are also used as receptors initiating the processes of colicin or phage binding and uptake. The functional activities of several outer membrane proteins in Escherichia coli K-12 were followed after cessation or repression of their synthesis. Cessation of receptor synthesis was accomplished with a thermolabile suppressor activity acting on amber mutations in btuB (encoding the receptor for vitamin B(12), the E colicins, and phage BF23) and in fepA (encoding the receptor for ferric enterochelin and colicins B and D). After cessation of receptor synthesis, cells rapidly became insensitive to the colicins using that receptor. Treatment with spectinomycin or rifampin blocked appearance of insensitive cells and even increased susceptibility to colicin E1. Insensitivity to phage BF23 appeared only after a lag of about one division time, and the receptors remained functional for B(12) uptake throughout. Therefore, possession of receptor is insufficient for colicin sensitivity, and some interaction of receptor with subsequent uptake components is indicated. Another example of physiological alteration of colicin sensitivity is the protection against many of the tonB-dependent colicins afforded by provision of iron-supplying siderophores. The rate of acquisition of this nonspecific protection was found to be consistent with the repression of receptor synthesis, rather than through direct and immediate effects on the tonB product or other components of colicin uptake or action.     

Changes in active transport, intracellular adenosine 5'-triphosphate levels, macromolecular syntheses, and glycolysis in an energy-uncoupled mutant of Escherichia coli.

The temperature-sensitive Escherichia coli mutant ecfts metC (Lieberman and Hong, 1974), previously shown to be defective in the coupling of metabolic energy to active transport, is also altered in a wide variety of cellular activities at the nonpermissive temperature. These alterations include a lowering of intracellular adenosine 5'-triphosphate levels, an alteration of glucose metabolism such that large quantities of pyruvate and dihydroxyacetone phosphate are excreted into the medium, excretion of accumulated potassium ions, and a cessation of deoxyribonucleic acid, ribonucleic acid, and phospholipid synthesis. Since these effects closely mimic the action of colicins E1 and K on E. coli cells, the possibility that the ecf gene product is the primary biochemical target for these colicins is discussed.