Patterns of Protein Synthesis in T5-infected Escherichia coli

Novel Escherichia coli RNA Polymerase Binding Protein Encoded by Bacteriophage T5

The Escherichia coli bacteriophage T5 has three temporal classes of genes (pre-early, early, and late). All three classes are transcribed by host RNA polymerase (RNAP) containing the σ⁷⁰ promoter specificity subunit. Molecular mechanisms responsible for the switching of viral transcription from one class to another remain unknown. Here, we find the product of T5 gene 026 (gpT5.026) in RNAP preparations purified from T5-infected cells and demonstrate in vitro its tight binding to E. coli RNAP. While proteins homologous to gpT5.026 are encoded by all T5-related phages, no similarities to proteins with known functions can be detected. GpT5.026 binds to two regions of the RNAP β subunit and moderately inhibits RNAP interaction with the discriminator region of σ⁷⁰-dependent promoters. A T5 mutant with disrupted gene 026 is viable, but the host cell lysis phase is prolongated and fewer virus particles are produced. During the mutant phage infection, the number of early transcripts increases, whereas the number of late transcripts decreases. We propose that gpT5.026 is part of the regulatory cascade that orchestrates a switch from early to late bacteriophage T5 transcription.

Calcium controls phage T5 infection at the level of the Escherichia coli cytoplasmic membrane

Phage T5 requires 0.1 mM calcium to produce phage progeny in Escherichia coli cells. Decreasing calcium below 0.1 mM at time phage DNA was transferred depleted the bacteria of K+, caused membrane depolarization, perturbation of phage DNA transfer and resulted in a low internal ATP level. Our data suggest that calcium controls the conformation of the channel involved in the transfer of phage DNA through the host envelope and that below 0.1 mM calcium the channel remains open. This creates an energetic state of the host unfavorable to the synthesis of phage components and leads to abortion of the infectious process.

Cell-free transcription and translation of isolated restriction fragments localize bacteriophage T5 pre-early genes

In vitro transcription and translation of isolated restriction fragments containing all or part of the terminal redundancies of bacteriophage T5 localized virtually every pre-early gene to a small 6.3-kilobase BglI fragment. Among these genes were those encoding the A1 and A2 proteins, which are responsible for complete entry of the viral genome into its host, and the deoxynucleoside 5'-monophosphatase. A 3.9-kilobase BglI fragment containing the remainder of the pre-early region induced no proteins under these same conditions. Proteins induced by fragments including the right and left terminal redundancies were also compared and found to be identical. DNA immediately flanking the pre-early regions induced few proteins in vitro. Thus, this technique has allowed the overall gene organization of the pre-early region of T5 to be described.

Phosphate repression of phage protein synthesis during infection by choleraphage phi 149

A synthetic medium for choleraphage phi 149 growth, in which the concentration of phosphate ions plays a significant role, has been defined. Upon infection, choleraphage phi 149 DNA binds to the cell membrane at three to four sites. The host macromolecular syntheses are shut off by 10 min after infection and the synthesis of phage-specific DNA is detectable after 20 min of infection. The phage utilizes primarily the host DNA degradation products for its own DNA synthesis. When added during the first 20 min of infection both nalidixic acid and novobiocin inhibit phage growth. The effects of these antibiotics are not pronounced when added late during infection. Pulse labeling of ultraviolet-irradiated infected cells at different times during infection has allowed identification of about 50 phage-specific proteins of which 19 are structural proteins. These proteins appear during the infection cycle in two distinct phases, early and late. When infection is carried out in high-phosphate medium, none of the late proteins is synthesized. Eleven of the 26 early proteins detected are DNA-binding proteins.

Second-step transfer of bacteriophage T5 DNA: purification and characterization of the T5 gene A2 protein

Second-step transfer of bacteriophage T5 DNA requires the function of the T5 pre-early proteins A1 and A2. We have isolated and characterized the gene A2 protein as part of an effort to determine the mechanism of second-step transfer. The A2 protein was purified by DNA-cellulose column chromatography followed by gel filtration and ion-exchange column chromatography. The A2 protein's identity was confirmed by two-dimensional gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and thin-layer gel filtration in 6 M guanidine hydrochloride demonstrated a molecular weight of 15,000 for the A2 polypeptide. Migration of the A2 protein through gel filtration columns under nondenaturing conditions, in combination with sedimentation behavior, indicated dimerization of the A2 polypeptide. The existence of the A2 dimer was confirmed by protein cross-linking with dimethyl suberimidate and analysis of the cross-linked proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amino acid composition, degree of polymerization, DNA-binding ability, and physical characteristics of the T5 gene A2 protein are consistent with a function of the A2 protein in DNA transfer.

Relationship between steps in 8-anilino-1-naphthalene sulfonate (ANS) fluorescence and changes in the energized membrane state and in intracellular and extracellular adenosine 5'-triphosphate (ATP) levels following bacteriophage T5 infection of Escherichia coli

The addition of bacteriophage T5 to anaerobic, fermenting cells of Escherichia coli B or K-12 in the presence of 8-anilino-1-naphthalene sulfonate (ANS), N-phenylnaphthyl-1-amine (NPN), or dansyl ethylamine causes the fluorescence of these probes to rise in two steps, the first occurring immediately upon addition, the second delayed by 6 min. The conditions necessary for observing this phenomenon are defined (cell density, probe concentration, substrate, absence of an electron acceptor, multiplicity of infection, growth, and harvesting conditions). The magnitudes of the first and second steps in fluorescence are dependent upon the multiplicity of infection; the timing of the steps is not. The first step correlates with a breakdown in the potassium or rubidium permeability barrier of the cells, and it occurs either aerobically or anaerobically, with fermentable or nonfermentable substrates. The second step occurs only with cells that are without an available electron acceptor, are fermenting, and which have a functional membrane-bound, Ca2+-dependent adenosine triphosphatase (ATPase). The results are consistent with disturbance of energization of the cell membrane by the membrane-bound ATPase at the time of the second step in fluorescence. No changes in the intracellular level of adenosine 5'-triphosphate (ATP) was seen, whereas the extracellular level increased sharply, starting 3--6 min after phage addition. The quantity of ATP found in the medium by 30 min after infection amounted to about four times the amount present inside the cells at the time of infection. The quantity and rate of efflux of ATP was similar under aerobic and anaerobic conditions.

Single-stranded bacteriophage T5 stO DNA as template for in vitro fMet-tRNA binding to ribosomes and protein synthesis

Good evidence is provided that fMet-tRNA binding and aminoacid incorporation, when single-stranded DNA is used instead of mRNA in an E. coli cell-free system, are strictly dependent on the magnesium concentration. Ten sites homologous to the initiation sites of translation can be detected on denatured T5 stO DNA when using ribosomes and initiation factors from uninfected E. coli F. In S-30 extracts, at high magnesium concentrations and in the presence of neomycin, initiation of the translation of denatured T5 stO DNA begins anywhere on the molecule, and yet high molecular weight polypeptides are synthesized. The template potentiality of the denatured T5 stO DNA decreased when using ribosomes plus initiation factors and crude extracts from T5 stO-infected bacteria. By in vitro formation of initiation complexes sites analogous to initiation sites of translation were localized on T5 stO DNA molecules using single-stranded fragments separated by sedimentation in alkaline sucrose gradient.

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.

Physical mapping of the HindIII, EcoRI, Sal and Sma restriction endonuclease cleavage fragments from bacteriophage T5 DNA

The DNA of bacteriophage T5+ (molecular weight 76 X 10(6) dalton) has been dissected by various specific endonucleases. The restriction enzymes HindIII and EcoRI produce 16 and 7 fragments respectively, whereas Sal and Sma produce 4 fragments each. Complete cleavage maps were established for the enzymes EcoRI, Sal and Sma and an almost complete map for HindIII. Furthermore the location and size of the deletions St 20, St 14, b3, St 0 and b1 were determined. The correlation of the genetic and functional map of the phage with the arrangement of fragments produced by the different enzymes has been established.

Structure and function of the genome of coliphage T5. Transcription in vitro of the "nicked" and "nick-free" T5+ DNA

Purified T5+ DNA in nicked form and after repair of the specific single-strand interruptions with DNA ligase was used in transcription studies using Escherichia coli RNA polymerase (holoenzyme) in the presence and absence of E. coli termination protein rho. The transcriptional products were analyzed with respect to their size distribution and the sequences transcribed from the different templates. The results indicate that the single-strand breaks in the DNA of bacteriophage T5, though in genetically defined positions, do not have any specific effect on transcription in vitro. Furthermore, the E. coli rho protein, although it depresses net RNA synthesis and reduces the average molecular weight of the transcripts, seems to act in a non-specific way in this system.

Regulation of expression of late genes of bacteriophage T5

Amber mutants of bacteriophage T5 defective in gene C2 have been characterized. The product of this gene is required for the normal turn-on of synthesis of late RNA's and proteins, and, apparently, for the normal continued synthesis of early RNA's and proteins during late stages of infection. The inability of nonpermissive cells to synthesize any proteins, either late or early, during the late period after infection with a C2-mutant is not due to premature lysis of the infected cells, to a depletion of the cellular energy supply, or to degradation of phage DNA at late times. A possible role for the product of gene C2 in early and late transcription of the viral genome is suggested.