Prophage terminase with tRNase activity sensitizes Salmonella enterica to oxidative stress

Phage viruses shape the evolution and virulence of their bacterial hosts. The Salmonella enterica genome encodes several stress-inducible prophages. The Gifsy-1 prophage terminase protein, whose canonical function is to process phage DNA for packaging in the virus head, unexpectedly acts as a transfer ribonuclease (tRNase) under oxidative stress, cleaving the anticodon loop of tRNALeu. The ensuing RNA fragmentation compromises bacterial translation, intracellular survival, and recovery from oxidative stress in the vertebrate host. S. enterica adapts to this transfer RNA (tRNA) fragmentation by transcribing the RNA repair Rtc system. The counterintuitive translational arrest provided by tRNA cleavage may subvert prophage mobilization and give the host an opportunity for repair as a way of maintaining bacterial genome integrity and ultimately survival in animals.

Characterization of endolysin from a Salmonella Typhimurium-infecting bacteriophage SPN1S

The full genome sequence of bacteriophage SPN1S, which infects Salmonella, contains genes that encode homologues of holin, endolysin and Rz/Rz1-like accessory proteins, which are 4 phage lysis proteins. The ability of these proteins to lyse Escherichia coli cells when overexpressed was evaluated. In contrast to other endolysins, the expression of endolysin and Rz/Rz1-like proteins was sufficient to cause lysis. The endolysin was tagged with oligohistidine at the N-terminus and purified by affinity chromatography. The endolysin has a lysozyme-like superfamily domain, and its activity was much stronger than that of lysozyme from chicken egg white. We used the chelating agent, ethylenediaminetetraacetic acid (EDTA), to increase outer membrane permeability, and it greatly enhanced the lytic activity of SPN1S endolysin. The antimicrobial activity of endolysin was stable over broad pH and temperature ranges and was active from pH 7.0 to 10.5 and from 25 °C to 45 °C. The SPN1S endolysin could kill most of the tested Gram-negative strains, but the Gram-positive strains were resistant. SPN1S endolysin, like lysozyme, cleaves the glycosidic bond of peptidoglycan. These results suggested that SPN1S endolysin has potential as a therapeutic agent against Gram-negative bacteria.

Restriction-modification system in bacteriophage MB78

Restriction-modification system is present in bacteria to protect the cells against phage infection. Interestingly, the bacteriophage MB78, a virulent phage of Salmonella typhimurium possesses restriction-modification system. Permissive host transformed with plasmid having the genomic fragment of MB78 carrying the putative restriction-modification genes severely restrict the growth of the phage 9NA. Growth of phage MB78 is also restricted to some extent. However, the temperate phage P22 is not restricted at all. Cloning of the the putative restriction-modification genes has been done in both orientations in different vectors. The clones carrying the genes in the same orientation as that of the lacZ in pUC19 are mostly unstable. However, those are stable when cloned in opposite orientation. Viability of the transformants is strain-, orientation-, and medium-dependent. The two genes have also been cloned individually/separately. Hosts carrying only the modification gene do not restrict growth of phages while the hosts carrying only the restriction gene do. The former produces stable transformants while the latter produces very unstable transformants which were viable only upto 36 h or so. The colonies carrying modification gene were normal looking while those carrying the restriction gene were tiny, flat, and looked distressed resembling very much the clones carrying bacterial restriction-modification system. Amplification of the genes and subsequent cloning in expression vector will be carried out for characterization of the enzymes.

Characterization of phi8, a bacteriophage containing three double-stranded RNA genomic segments and distantly related to Phi6

The three double-stranded RNA genomic segments of bacteriophage Phi8 were copied as cDNA, and their nucleotide sequences were determined. Although the organization of the genome is similar to that of Phi6, there is no similarity in either the nucleotide sequences or the amino acid sequences, with the exception of the motifs characteristic of viral RNA polymerases that are found in the presumptive polymerase sequence. Several features of the viral proteins differ markedly from those of Phi6. Although both phages are covered by a lipid-containing membrane, the protein compositions are very different. The most striking difference is that protein P8, which constitutes a shell around the procapsid in Phi6, is part of the membrane in Phi8. The host attachment protein consists of two peptides rather than one and the phage attaches directly to the lipopolysaccharide of the host rather than to a type IV pilus. The host range of Phi8 includes rough strains of Salmonella typhimurium and of pseudomonads

Characterization of a novel DNA primase from the Salmonella typhimurium bacteriophage SP6

The gene for the DNA primase encoded by Salmonella typhimurium bacteriophage SP6 has been cloned and expressed in Escherichia coli and its 74-kDa protein product purified to homogeneity. The SP6 primase is a DNA-dependent RNA polymerase that synthesizes short oligoribonucleotides containing each of the four canonical ribonucleotides. GTP and CTP are both required for the initiation of oligoribonucleotide synthesis. In reactions containing only GTP and CTP, SP6 primase incorporates GTP at the 5'-end of oligoribonucleotides and CMP at the second position. On synthetic DNA templates, pppGpC dinucleotides are synthesized most rapidly in the presence of the sequence 5'-GCA-3'. This trinucleotide sequence, containing a cryptic dA at the 3'-end, differs from other known bacterial and phage primase recognition sites. SP6 primase shares some properties with the well-characterized E. colibacteriophage T7 primase. The T7 DNA polymerase can use oligoribonucleotides synthesized by SP6 primase as primers for DNA synthesis. However, oligoribonucleotide synthesis by SP6 primase is not stimulated by either the E. coli- or the T7-encoded ssDNA binding protein. An amino acid sequence alignment of the SP6 and T7 primases, which share only 22.4% amino acid identity, indicates amino acids likely critical for oligoribonucleotide synthesis as well as a putative Cys(3)His zinc finger motif that may be involved in DNA binding.

Characterization of two restriction endonucleases, SenPT14bI and SenPT16I, in standard phage-type strains of Salmonella enteritidis

Two restriction endonucleases (ENases) were found by screening 38 standard phage strains of Salmonella (S.) Enteritidis. An isoschizomer of SacII ENase that recognizes the sequence 5'-CCGC/GG-3' was identified in S. Enteritidis PT14b, and an isoschizomer of XmaIII ENase (5'-C/GGCCG-3') was found in S. Enteritidis PT16. It is of special interest that the recognition specificities of all known ENases in Salmonella, including those of the S. Enteritidis ENases, are very similar to each other.

T7 DNA-dependent RNA polymerase can transcribe RNA from tick-borne encephalitis virus (TBEV) cDNA with SP6 promoter

T7 RNA polymerase is shown to recognize the SP6 promoter including 17 base pairs before the transcription start site and produce the 5'-end TBEV RNA. The yield of TBEV RNA synthesized by heterologous T7 RNA polymerase from cDNA construction with SP6 promoter is higher than the RNA production by homologous SP6 RNA polymerase. The addition of 1 pmol template DNA with SP6 17 bp promoter in transcription mixture for SP6 or T7 RNA polymerases resulted in a 1-5 X 10(-2) pmol RNA production.

Transcription by SP6 RNA polymerase exhibits an ATP dependence that is influenced by promoter topology

Transcription of linearized DNA templates by SP6 RNA polymerase requires a higher concentration of ATP than of the other three nucleotides. This requirement is not shared by T7 RNA polymerase. The ATP requirement is partially relieved when the SP6 template is supercoiled but not when it is relaxed circular DNA. The effect of supercoiling is eliminated by replacement of the A.T rich sequence downstream from the SP6 promoter with a G.C rich sequence. Examination of the reaction products indicates that the ATP dependence of transcription from a linear template is not due to an ATPase activity or to the premature termination of transcription at low ATP concentration. These data suggest that the initiation of transcription by SP6 RNA polymerase requires partial denaturation of the template in the promoter-proximal region, and that this requirement can be satisfied by negative supercoiling or by increasing the ATP concentration. ATP also reduces, but does not eliminate, the abortive transcription that leads to the production of short, prematurely terminated transcripts by SP6 polymerase from supercoiled templates.

Reexamination of the role of Asp20 in catalysis by bacteriophage T4 lysozyme

Replacement of Asp20 in T4 lysozyme by Cys produces a variant with (1) nearly wild-type specific activity, (2) a newly acquired sensitivity to thiol-modifying reagents, and (3) a pH-activity profile that is very similar to that of the wild-type enzyme. These results indicate that the residue at position 20 has a significant nucleophilic function rather than merely an electrostatic role. The intermediate in catalysis by lysozyme is probably a covalent glycosyl-enzyme instead of the ion pair originally proposed.

Thermal unfolding pathway for the thermostable P22 tailspike endorhamnosidase

The conditions in which protein stability is biologically or industrially relevant frequently differ from those in which reversible denaturation is studied. The trimeric tailspike endorhamnosidase of phage P22 is a viral structural protein which exhibits high stability to heat, proteases, and detergents under a range of environmental conditions. Its intracellular folding pathway includes monomeric and trimeric folding intermediates and has been the subject of detailed genetic analysis. To understand the basis of tailspike thermostability, we have examined the kinetics of thermal and detergent unfolding. During thermal unfolding of the tailspike, a metastable unfolding intermediate accumulates which can be trapped in the cold or in the presence of SDS. This species is still trimeric, but has lost the ability to bind to virus capsids and, unlike the native trimer, is partially susceptible to protease digestion. Its N-terminal regions, containing about 110 residues, are unfolded whereas the central regions and the C-termini of the polypeptide chains are still in the folded state. Thus, the initiation step in thermal denaturation is the unfolding of the N-termini, but melting of the intermediate represents a second kinetic barrier in the denaturation process. This two-step unfolding is unusually slow at elevated temperature; for instance, in 2% SDS at 65 degrees C, the unfolding rate constant is 1.1 x 10(-3) s-1 for the transition from the native to the unfolding intermediate and 4.0 x 10(-5) s-1 for the transition from the intermediate to the unfolded chains. The sequential unfolding pathway explains the insensitivity of the apparent Tm to the presence of temperature-sensitive folding mutations [Sturtevant, J. M., Yu, M.-H., Haase-Pettingell, C., & King, J. (1989) J. Biol. Chem. 264, 10693-10698] which are located in the central region of the chain. The metastable unfolding intermediate has not been detected in the forward folding pathway occurring at lower temperatures. The early stage of the high-temperature thermal unfolding pathway is not the reverse of the late stage of the low-temperature folding pathway.

Mechanism of nitrofuran resistance in Salmonella enteritidis phage type 4 and interpretation of nitrofuran susceptibility tests

The mechanism of nitrofuran resistance in Salmonella enteritidis phage type 4 was studied. Nitrofuran reductase activity was inversely related to the furazolidone MIC for the organism. Strains with low-level nitrofuran resistance, typically found in almost all isolates of S. enteritidis PT4, had intermediate nitrofuran reductase activity. Disc diffusion tests with furazolidone, 15 or 50 micrograms discs, and nitrofurantoin, 50 or 300 micrograms discs, failed to distinguish reliably between susceptible populations and those with low-level resistance. In order to detect low-level resistance to nitrofurans a dilution method should be used with a furazolidone breakpoint of 1 mg/l or a nitrofurantoin breakpoint of 16 mg/l.

Properties of monoclonal antibodies selected for probing the conformation of wild type and mutant forms of the P22 tailspike endorhamnosidase

Eleven species of monoclonal antibodies directed against the trimeric P22 tailspike endorhamnosidase have been selected and characterized. Seven of these antibodies recognize the native tailspike, both isolated and assembled onto the virion, and prevent phage infection. Four antibodies react with denatured forms of the tailspike as well as with the plastic absorbed tailspike. Three of these latter prevent the tailspike from assembling onto the phage head. The antibodies have been tested against tailspike proteins carrying single amino acid substitutions at 15 different sites on the protein. Two of these mutations interfere with binding by a set of the monoclonals, indicating that they disrupt the epitopes for these antibodies. Since amino acid replacements corresponding to the temperature-sensitive folding mutations do not change the conformation of the native protein, these mutant proteins may be particularly useful for mapping epitopes. Amber fragments of the tailspike chain are recognized predominantly by the anti-denatured antibodies suggesting either that they are conformationally closer to folding intermediates than to the native tailspike or that the epitopes recognized by anti-native antibodies are carried by the C-terminal end of the native protein. Immunochemical detection by an anti-denatured antibody, after sucrose gradient sedimentation of a large 55-kDa amber fragment, indicates a monomeric rather than a trimeric state. This suggests that the missing C-terminal region is important for the trimerization reaction. Such N-terminal amber fragments may be useful models for studying with the monoclonal antibodies the nascent chain emerging from the ribosome.

A molecular analysis of terminase cuts in headful packaging of Salmonella phage P22

Fragments of DNA molecules of Salmonella phage 22 which represent the molecular termini created by the terminase reaction have been cloned and sequenced. The terminase cleavage separates a headful-sized piece of DNA from the concatemeric precursor; by successful cloning strategy it was shown that the terminase produces blunt ends. The termini of 20 different phage DNA molecules fall into a region located between about 600 and 4000 bp from the pac signal and show a Gaussian distribution. The average terminal redundancy was calculated to be about 2230 bp (= 5.3%) and is therefore higher than was previously reported. A comparison of the nucleotides flanking the terminal bases of 20 different end clones does not support the suggestion that the terminase recognizes some specific sequence and/or structural information in determining the actual cleavage site.

Analysis in vivo of the bacteriophage P22 headful nuclease

Bacteriophage P22 packages its double-stranded DNA chromosomes from concatemeric replicating DNA in a processive, sequential fashion. According to this model, during the initial packaging event in such a series the packaging apparatus recognizes a nucleotide sequence, called pac, on the DNA, and then condenses DNA within the coat protein shell unidirectionally (rightward) from that point. DNA ends are generated near the pac site before or during the condensation reaction. The right end of the mature chromosome is created by a cut made in the DNA by the "headful nuclease" after a complete chromosome is condensed within the phage head. Subsequent packaging events on that concatemeric DNA begin at the end generated by the headful cut of the previous event and proceed in the same direction as the previous event. We report here accurate measurements of the P22 chromosome length (43,400( +/- 750) base-pairs, where the uncertainty is the range in observed lengths), genome length (41,830( +/- 315) base-pairs, where the uncertainty represents the accuracy with which the length is known), the terminal redundancy (1600( +/- 750) base-pairs or 3.8( +/- 1.8)%, where the uncertainty is the observed range) and the imprecision in the headful measuring device ( +/- 750 base-pairs or +/- 1.7%). In addition, we present evidence for a weak nucleotide sequence specificity in the headful nuclease. These findings lend further support to, and extend our understanding of, the sequential series model of P22 DNA packaging.

Nucleotide sequence and expression of the cloned gene of bacteriophage SP6 RNA polymerase

The coding region of the gene for bacteriophage SP6 RNA polymerase was cloned into pBR322, and its entire nucleotide sequence was deduced. The predicted amino acid sequence for the polymerase consists of 874 amino acid residues with a total molecular weight of 98,561 daltons. Comparison of the amino acid sequence with that of T7 RNA polymerase reveals that regions with partial homology are present along the sequence. The coding region of SP6 RNA polymerase was inserted into an E. coli expression vector. The polymerase gene was efficiently expressed in E. coli cells, and the enzymatic properties of the expressed polymerase were very similar to those of the enzyme synthesized in SP6 phage-infected Salmonella typhimurium cells.

Purification and properties of RNA polymerase of phage KB1

Bacteriophage KB1 belongs to group C of Bradely's classification After infection a bacteriophage specific RNA polymerase is induced in infected cells. KB1 RNA polymerase is a stable enzyme and is easily purified to homogeneity in good overall yield. The activity resides in a single polypeptide chain of molecular weight about 90,000. Synthesis of RNA by KB1 RNA polymerase requires a DNA template and Mg++ and like SP6 RNA polymerase, is strongly stimulated by either bovine serum albumin or spermidine. Thiol reactive reagents inhibit the enzyme, suggesting the presence of essential sulfhydryl residues. The enzyme possess a stringent promoter specificity. The KB1 RNA polymerase is also highly active in synthesis of poly(rG) with poly(dI).(dC) as template. My experiments suggest that the catalytic portion of the polymerase can be separated from the RNA polymerase holoenzyme.

Purification and characterization of bacteriophage 9NA lysozyme

Bacteriophage 9NA is a virulent phage of Salmonella typhimurium which induces a lysozyme in host cells toward the later stages of its multiplication. 9NA lysozyme has been purified about 1000 fold starting from the lysate of 9NA infected cells. The enzyme has an optimum pH between 7 and 8 and its activity is dependent on the ionic strength of the assay medium. Salts like NaCl and KCl are inhibitory to the lysozyme. Gram-negative cells act as better substrate for the lysozyme than do Gram-positive cells. The enzyme has a molecular weight of about 2.1 X 10(4) and rapidly loses its activity at temperatures higher than 45 degrees C. The properties of 9NA lysozyme have been compared with those of T4, lambda and P22 lysozymes.

Plasmids allowing transcription of cloned DNA by Salmonella typhimurium phage SP6 RNA polymerase to produce RNAs with authentic 5'-terminal sequences

We wished to determine whether there is any specific sequence downstream of the start point of the SP6 promoter which is required for its function in the plasmid pSP64 (Melton et al., 1984). Lack of such specificity would permit in vitro synthesis of an RNA molecule having a 5'-terminal sequence identical to its wild-type in vivo counterpart. To test its requirement, we replaced all of the SP6 sequence downstream of the transcription start point with heterologous nucleotides (nt) and found that any sequence will suffice to permit efficient and accurate transcription. These results permitted construction of plasmids for synthesis of 'authentic' transcripts from cloned DNA. In one case, by an oligodeoxynucleotide-mediated site-specific deletion, we placed the start point of yeast gene TCM1 at nt + 2 of the SP6 promoter and produced in vitro TCM1 mRNA with a wild-type 5'-terminal sequence. We also constructed a vector, pSP64 delta 1, in which the SalI/AccI/HincII recognition sites of pSP64 reside at nt + 2 through + 7. Plasmids such as pSP64 delta 1 may be more useful in some cases as insertion of any DNA fragment at one of these three sites will yield a transcript in which only two to four nt are derived from the vector.

Structure of phage P22 gene 19 lysozyme inferred from its homology with phage T4 lysozyme. Implications for lysozyme evolution

The amino acid sequence of the lysozyme from phage P22 is shown to be homologous (26% identity) with the lysozyme from bacteriophage T4. The sequence correspondence suggests that the structure of P22 lysozyme is similar to the known structure of T4 lysozyme within the "core" of the molecule, including the active site cleft. However, P22 lysozyme appears to lack two surface loops present in T4 lysozyme. It is possible that P22 lysozyme may provide an "evolutionary link" between the phage-type lysozymes and the goose-type lysozymes.

Single amino acid substitutions influencing the folding pathway of the phage P22 tail spike endorhamnosidase

Temperature-sensitive mutations in the gene for the thermostable tail spike of phage P22 interyFere with the folding and subunit association pathway at the restrictive temperature but not with the activity or stability of the protein once matured. The local sites of these mutations and the mutant amino acid substitutions have been determined by DNA sequencing. Of 11 temperature-sensitive folding mutations, 3 were replacements of glycine residues by polar residues, and three were replacements of threonine residues by residues unable to form a side-chain H-bond. There were no proline replacements. Two of the temperature-sensitive sites in which threonine residues were replaced by isoleucine residues were homologous. These sequences probably maintain the correct local folding pathway at higher temperatures. The temperature-sensitive amino acid substitutions appear to destabilize a thermolabile intermediate in the wild-type folding pathway or to increase the rate of a competing off-pathway reaction.

Characterization of an R-plasmid dihydrofolate reductase with a monomeric structure

A plasmid-encoded dihydrofolate reductase that originated in a clinical isolate of Salmonella typhimurium (phage type 179) moderately resistant to trimethoprim has been isolated and characterized. The dihydrofolate reductase (called type III) was purified to homogeneity using a combination of gel filtration, hydrophobic chromatography, and methotrexate affinity chromatography. Polyacrylamide gel electrophoresis under denaturing and nondenaturing conditions indicated that the enzyme is a 16,900 molecular weight monomeric protein. Kinetic analyses showed that trimethoprim is a relatively tight binding inhibitor (Ki = 19 nM) competitive with dihydrofolate. The enzyme is also extremely sensitive to methotrexate inhibition (Ki = 9 pM) and has a high affinity for dihydrofolate (Km = 0.4 microM). The sequence of the first 20 NH2-terminal residues of the protein shows 50% homology with the trimethoprim-sensitive chromosomal Escherichia coli dihydrofolate reductase and suggests that the two enzymes may be closely related. This is the first example of a plasmid encoding for a monomeric dihydrofolate reductase only moderately resistant to trimethoprim, and a resistance mechanism, dependent in part on the high dihydrofolate affinity of the type III enzyme, is proposed.

Maturation of the tail spike endorhamnosidase of Salmonella phage P22

As part of a genetic analysis of the in vivo folding and subunit assembly of the P22 tail spike endorhamnosidase, we have studied the maturation of the newly synthesized 76,000-dalton polypeptide chains into thermostable tail spike oligomers. Four of 15 temperature-sensitive mutations in the structural gene for this protein result in electrophoretically distinct tail spikes. Cells mixedly infected with wild type and an electrophoretic variant produce two hybrid species, with mobilities intermediate between the parental species, indicating that the native tail spike is a trimer. Mature trimers are resistant to denaturation by sodium dodecyl sulfate (SDS): at room temperature the trimer migrates in an SDS gel as if it were not binding significant amounts of SDS, whereas the heat-denatured chain migrates as expected of an SDS-polypeptide complex. The mature trimer is also resistant to trypsin digestion. Lysates of infected cells contain SDS and trypsin-sensitive forms of the newly synthesized tail spike polypeptide chains. These are probably incompletely or incorrectly folded chains. SDS and trypsin resistance were used to measure the efficiency of in vivo folding and subunit assembly of the mature trimer from its polypeptide chains. This decreased from 90% at 27 degrees C to only 15% at 42 degrees C. These results are consistent with the existence or a labile intermediate or step in the folding or subunit assembly of the thermostable tail spike protein. We discuss the possibility that the achievement of certain structural features of mature proteins may entail difficulties in their folding pathways.

Trimeric intermediate in the in vivo folding and subunit assembly of the tail spike endorhamnosidase of bacteriophage P22

Newly synthesized tail spike polypeptide chains mature from trypsin- and NaDodSO4-sensitive unfolded chains to trypsin- and NaDodSO4-resistant native trimers with a t1/2 of 5 min at 30 degrees C. A metastable intermediate in subunit folding and assembly was trapped by chilling and isolated by electrophoresis through nondenaturing gels in the cold. A fraction of the intermediate could be matured into native trimers in vitro by incubating at physiological temperature. Mixing experiments with electrophoretically distinct mutant proteins showed that the precursor that matured in vitro represented three tail spike polypeptide chains already associated with each other but not fully folded. Identification of this intermediate reveals that the processes of polypeptide chain folding and subunit assembly are coupled in this large structural protein.

Bacteriophage SP6-specific RNA polymerase. I. Isolation and characterization of the enzyme

SP6 is a small, virulent bacteriophage which grows on Salmonella typhimurium LT2. It is morphologically similar to Escherichia coli bacteriophage T7 and its relatives, but appears to be genetically distinct. After infection a bacteriophage-specific RNA polymerase is induced in infected cells. SP6 RNA polymerase is a stable enzyme and is easily purified to homogeneity in good overall yield. The activity resides in a single polypeptide chain of Mr = 96,000. Synthesis of RNA by SP6 RNA polymerase requires a DNA template and Mg2+ ion and is strongly stimulated by either bovine serum albumin of spermidine. Thiol-reactive reagents inhibit the enzyme, suggesting the presence of essential sulfhydryl residues. RNA synthesis requires native SP6 RNA as template; DNAs from other bacteriophages including T3 and T7 are inert; hence, SP6 RNA polymerase possesses a stringent promoter specificity similar to, but distinct from that of the other phage RNA polymerases. The SP6 RNA polymerase is also highly active in synthesis of poly(rG) with poly(dI) . (dC) as template. This reaction is unlikely to involve promoter-like sites, but it appears to reflect a general catalytic capacity of the polymerase, since cleavage of the SP6 RNA polymerase with trypsin, which completely eliminates SP6-transcribing activity, has little effect on poly(rG) synthesis. Hence, it appears that the catalytic portion of the polymerase can be separated from the RNA polymerase holoenzyme.

Salmonella bacteriophage glycanases: endorhamnosidase activity of bacteriophages P27, 9NA, and KB1

Four bacteriophages, P22, P27, 9NA, and KB1, active on smooth Salmonella strains belonging to serogroups A, B, and D1 were investigated for endoglycosidase activity and specificity in enzyme hydrolysis assays. Purified phage was incubated with phenol-water-extracted lipopolysaccharide preparations which had been partially delipidated. Dialyzable oligosaccharides, released by phage glycosidase activity, were analyzed by sugar and methylation analyses. Phages P27, 9NA, and KB1, as well as P22 assayed earlier (U. Eriksson et al., J. Gen. Virol. 43: 503-511, 1979; S. Iwashita and S. Kanegasaki, Biochem. Biophys. Res. Commun. 55:403-409, 1973), were all found to have phage-associated endorhamnosidase activity hydrolyzing the O-polysaccharide chain common to bacteria of serogroups A, B, and D1 [Formula: see text] between the l-rhamnose and d-galactose residues. The nature of the R monosaccharide, abequose, tyvelose, or paratose, had no effect on the activity or specificity of the endorhamnosidase, whereas a change of the d-galactose --> d-mannose linkage from alpha1,2 to alpha1,6 made the O-polysaccharide chain resistant to the endorhamnosidases. Modification of the O chain by glucosylation of the d-galactose residue at O-4 or O-6 revealed two glycosidase specificities: the phage P22 and P27 enzymes hydrolyzed O chains glucosylated at O-4 but not O-6, whereas the phage 9NA and KB1 enzymes hydrolyzed chains glucosylated at O-6 but not O-4. Phage KB1, like P22 and P27, had a short, noncontractile tail containing a base plate with tail spikes (morphologically Bradley group C), whereas 9NA had a long, flexible tail ending with a base plate-like appendage (Bradley group B), which suggests that the endorhamnosidase activity can be associated with different tail structures.

Salmonella bacteriophage glycanases: endorhamnosidases of Salmonella typhimurium bacteriophages

Twelve bacteriphages lysing only smooth Salmonella typhimurium strains were shown to have similar morphology--an icosahedric head to which a short, noncontractile tail carrying six spikes was attached. All phages degraded their lipopolysaccharide (LPS) receptors as shown by their ability to cleave off [14C]galactosyl-containing oligosaccharides from S. typhimurium cells labeled in their LPS. The oligosaccharides inhibited the alpha-D-galactosyl-specific Bandeiraea simplicifolia lectin agglutination of human type B erythrocytes, indicating that all 12 phage glycanases were of endorhamnosidase specificity, i.e., hydrolyzed the alpha-L-rhamnopyranosyl-(1 leads to 3)-D-galactopyranosyl linkage in the S. typhimurium O-polysaccharide chain. Two of the phages, 28B and 36, were studied in more detail. Whereas the phage 28B glycanase hydrolyzed the S. typhimurium LPS into dodeca- and octasaccharides, the phage 36 glycanase in addition cleaved off tetrasaccharides. Both phage enzymes hydrolyzed the O-polysaccharide chains of LPS from Salmonella belonging to serogroups A, B, and D1, which are built up of tetrasaccharide-repeating units identical except for the nature of the 3,6-dideoxyhexopyranosyl group (R). : FORMULA:(SEE TEXT). The phage 28B and 36 endorhamnosidases hydrolyzed also an LPS from which the 3,6-dideoxyhexosyl substituents had previously been hydrolyzed off. However, neither of the enzymes was active on LPS preparations in which the C2-C3 bond of the L-rhamnopyranosyl ring had been opened by periodate oxidation. Glucosylation at O-6 of the D-galactopyranosyl residues in the S. typhimurium LPS was found to be incompatible with hydrolysis by both enzymes. However, in an LPS glucosylated at O-4 of the D-galactopyranosyl residues, the adjacent alpha-L-rhamnopyranosyl linkages were found to be perferentially cleaved.

Regulation of late functions in Salmonella bacteriophages P22 and L studied by assaying endolysin synthesis

The rate of endolysin synthesis in Salmonella typhimurium cells infected by bacteriophage P22 or L was taken as a measure for the activity of 23 gene product (the positive regulator for the "late" genes of P22 and L). Endolysin in coded for by gene 19. The amber mutations in gene 23 of P22 and L, used in this study, reduced the rate of endolysin synthesis by a factor of ca. 90 for P22 and of ca. 20 for L. In mixed infections with 19- and 23- mutants the 23 gene products of P22 and L ACT As positive regulators for the respective gene 19 in cis and in trans. Cross-specificity of the 23 gene products, i.e., turning on expression of gene 19 on a chromosome of the other species, could not be demonstrated.

Salmonella phage glycanases: substrate specificity of the phage P22 endo-rhamnosidase

Interaction between phage P22 and phenol-water extracted lipopolysaccharides from sensitive Salmonella bacteria belonging to serogroups A, B and Di results in hydrolysis of the alpha-L-rhamnosyl linkages within the tetrasaccharide repeating unit of the O-antigenic polysaccharide chain. These O-antigens have identical structures except for the nature of the 3,6-dideoxy-hexosyl group linked to O-3 of the D-mannosyl residue. Removal of the dideoxysugar, or periodate oxidation followed by borohydride reduction of the L-rhamnosyl residue made the O chain resistant to the endo-rhamnosidase. Substitution of the D-galactosyl residue at O-4, but not at O-6, with an alpha-D-glucosyl group was compatible with hydrolysis. A number of Klebsiella pneumoniae and Shigella flexneri lipo- or capsular polysaccharides containing chain L-rhamnosyl residues were tested but none was sensitive to the P22 endo-rhamnosidase. The substrate specificity of the endo-rhamnosidase parallels the lytic specificity of the phage which suggests that the initial step in phage P22 infection is a P22 tail enzyme O-antigen substrate interaction. The main product of the hydrolysate was octa-, dodeca- and hexadecasaccharides. Treatment of phage FO resistant smooth strains of S. typhimurium with P22 tails removed O polysaccharide chains and made previously 'hidden' FO receptors accessible to the phage.

Adsorption of phage P22 to Salmonella typhimurium

Adsorption of phage P22 to its receptor in the lipopolysaccharide (LPS) of the envelope of Salmonella typhimurium is accompanied by a hydrolytic cleavage of the O polysaccharide chain. The enzyme, and endorhamnosidase, is found in the phage tail. Propagation of a mutant of phage P22, containing two amber mutations, under restrictive conditions permitted isolation of phage tail parts with endorhamnosidase activity. The tail parts, purified by ion exchange chromatography, were shown to be homogenous by polyacrylamide gradient gel electrophoresis, isoelectric focusing in polyacrylamide gel electrophoresis and crossed immunoelectrophoresis. The mol. wt. was estimated to 240000. The optimal pH range for glycosidase activity was 5 to 7 and optimal temperature 37 degrees C. Hydrolysis of the O polysaccharide chain, when estimated with whole bacteria as the substrate, did not seem to be influenced by the cation concentration. Eclipse of P22 phage particles to whole bacteria was likewise uninfluenced by the cation concentration in the reaction mixture, but eclipse by isolated receptor containing LPS required cations. The optimal concentration for divalent cations was 2 X 10(-3) M, for trivalent cations 1 X 10(-3) M.

New deoxyribonuclease activity after bacteriophage P22 infection

Extracts from P22-infected and uninfected cultures of Salmonella typhimurium were subjected to deoxyribonucleic acid (DNA)-cellulose and diethylaminoethyl-cellulose chromatography. Comparison of the elution patterns revealed that in infected cells there is a decrease in the amount of nuclease activity specific for denatured DNA and an increase in the amount of nuclease activity specific for native DNA. The latter activity was shown to differ from a similar host enzyme in Mg(2+), Mn(2+), and pH optima. This new activity is not found after infection of a lysogen with a nonvirulent phage or after infection under nonpermissive conditions with P22ts25.1 (a mutant in gene 25 that carries out no known functions other than adsorption and injection) and thus appears to be specified by the phage genome.