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119 records · Page 7Linked to original sources
PubMed1969

Delayed lysis with a mutant of salmonella bacteriophage p22.

A mutant of bacteriophage P22 (Lys(-)) was isolated which shows a plaque morphology on mixed plates comparable to the r(+) plaques of the T-even phages. When Lys(-) and normal Lys(+) plaques are juxtaposed on a petri dish, the Lys(+) plaque exhibits a flat side adjacent to the Lys(-) plaque. The mutant is identical to P22 under an electron microscope, is inactivated at the same rate by antiserum and heat, and has the same kinetics of attachment. It does not plate on Salmonella lysogenic for phage P22 nor on strain St/22. In liquid culture, the lysis of mutant infections in M9CAA medium is delayed between 20 and 40 min. Cells mixedly infected in M9CAA with Lys(-) and Lys(+) phage lyse later than Lys(+)-infected cells and even later than Lys(-)-infected cells. In unsupplemented M9 medium, however, mixedly infected cells again lyse later than Lys(+)-infected cells, but Lys(-)-infected cells require more than 3 hr to lyse. In supplemented and unsupplemented M9 media, intracellular phage development and endolysin synthesis proceed in Lys(-) infections at least as rapidly as in Lys(+)-infected cells. In diluted infections, the latent and eclipse periods of Lys(-) and Lys(+) infections are indistinguishable. The possible mechanisms involved in the control and timing of lysis are discussed.

Journal Article↗
PubMed1985

Genetic and DNA mapping of the late regulation and lysis genes of Salmonella bacteriophage P22 and coliphage lambda.

Genetic and DNA heteroduplex analyses of lambda imm22 hybrid phages were used to compare the Salmonella bacteriophage P22 and coliphage lambda genes which control late gene regulation and lysis. Homologous DNA sequences were correlated with P22 gene 23 and lambda gene Q (late gene regulation) and with P22 gene 13 and lambda gene S (lysis control). Nonhomologous DNA sequences were correlated with P22 gene 19 and lambda gene R (lysozyme and endolysin) and with the region encoding the P22 alpha and lambda 6S transcripts.

Bacteriophage lambda↗
PubMed1994

Cloning, molecular characterization, and expression of the genes encoding the lytic functions of lactococcal bacteriophage phi LC3: a dual lysis system of modular design.

The genes encoding the lysis proteins of Lactococcus lactis bacteriophage phi LC3 were cloned, sequenced, and expressed in Escherichia coli. The phi LC3 lysis genes, lysA and lysB, encode a membrane-disrupting protein (LysA) of 88 amino acids, and a cell wall degrading protein (LysB) of 429 amino acids, which shares significant sequence similarity with lysins from the Streptococcus pneumoniae phages Cp-1, Cp-7, and Cp-9, and Lactobacillus delbrueckii phage mv1. Both LysA and LysB function in E. coli, as judged by lysis of the E. coli host cells and by lytic activity against lactococcal cells when the cloned lysA and lysB genes are expressed. The LysA protein possesses two putative transmembrane helices and highly charged N- and C-termini, and is structurally similar to phage holins that are known to induce lesions in the inner membrane through which phage endolysin can be released to its cell wall substrate. The C-terminal end of LysB contains two highly homologous sequence repeats of 43 amino acids. The LysB repeats show strong sequence similarity to repeats found in lytic enzymes from other Gram-positive bacteria and from Bacillus subtilis phage phi 29 and PZA, as well as in some functionally unrelated proteins, and they are possibly involved in binding of the enzyme to the cell wall substrate. The organization of the dual phi LC3 lysis system supports earlier suggestions that exchange of modular units is an important principle in protein evolution.

Amino Acid Sequence↗
PubMed2026

The Convergence of Antimicrobial Resistance and Virulence in Streptococcus pneumoniae: A Molecular and Clinical Perspective.

Antimicrobial resistance (AMR) and virulence have traditionally been viewed as competing traits in bacterial evolution due to fitness costs. However, Streptococcus pneumoniae has emerged as a paradigm of successful coevolution, with multidrug-resistant clones simultaneously maintaining or enhancing pathogenic potential. This review examines the molecular mechanisms, epidemiological patterns, and clinical consequences of the convergence between AMR and virulence in Streptococcus pneumoniae. Resistance to β-lactams is driven by mosaic penicillin-binding protein genes (pbp1a, pbp2b, pbp2x), while macrolide resistance is mediated primarily by the erm(B) gene (MLS phenotype) and mef(A/E)-msr(D) genes encoding an efflux system. These determinants are frequently co-localized on integrative and conjugative elements, ICEs, (e.g., Tn916 family) within successful clonal complexes such as CC271/320 and lineages including ST320 and GPSC10. Contrary to the classical fitness cost hypothesis, compensatory epistasis, capsular recombination, metabolic adaptations, and intra-serotype phenotypic variation enable certain clones to combine high-level resistance to β-lactams, macrolides, and tetracyclines with enhanced colonization, biofilm formation, immune evasion, and invasive capacity. Post-pneumococcal conjugate vaccine (PCV) surveillance reveals the persistence and expansion of these high-risk lineages, contributing to treatment-refractory invasive pneumococcal disease (IPD), increased morbidity, and mortality. Although PCVs have reduced vaccine-type resistant strains in some settings, serotype replacement and emerging metabolic genotypes continue to drive adaptation. This review highlights the need for integrated genomic surveillance, novel therapeutics (e.g., omadacycline, lefamulin, endolysins), monoclonal antibodies, and next-generation vaccines targeting both resistance and conserved virulence determinants. A multifaceted strategy combining antimicrobial stewardship, strengthened surveillance, and innovative interventions is essential to curb the evolving threat of resistant and virulent S. pneumoniae.

Streptococcus pneumoniae↗
PubMedDate not supplied

[Homology of lysozymes of bacterial and vertebrate origin].

Theoretical analysis of structural and functional organization of vertebrate lysozymes, T4-phage lysozyme, lambda-phage endolysin and extracellular lysozyme of Chalaropsis species suggests a genetic relationship between the enzymes in question. It has been shown that the lysozyme sequences exhibit both inter- and intramolecular homology. The obtained data lend support to the concept postulating a common ancestor for the lysozyme family and subsequent divergent evolution of these proteins. The two-component primary structure of lysozymes can result from structural gene duplication and allows to explain similar catalytic activity and different substrate specificity of these enzymes by the differentiation and specialization of functions of the N- and C-components of the protein chains.

Amino Acid Sequence↗
PubMed1983

Purification of the bacteriophage lambda late gene regulator encoded by gene Q.

The product of bacteriophage lambda gene Q is a transcription antiterminator that activates phage late gene expression. We report a method to purify the lambda Q protein to near homogeneity. We have followed during purification both activity of Q protein to provoke in vitro synthesis of the lambda late protein endolysin in the DNA-dependent protein-synthesizing system, and radioactivity in a polypeptide that we show by genetic criteria to be lambda Q. These co-purify throughout the procedure.

Bacteriophage lambda↗
PubMed1981

Screening of carcinogens with the prophage lambda cIts857 induction test.

The prophage lambda cIts857 induction test with Escherichia coli K12 envA uvrB as the lysogen has been successfully applied to the screening of sparingly water-soluble carcinogens that have been dissolved in dimethyl sulfoxide and metabolically activated with liver enzymes induced either with Aroclor 1254 or phenobarbital. Growth of noninduced lysogenic cells during the test was suppressed with ampicillin, with resultant increase of sensitivity of the test. The maximum inducing activity observed was about 50% of the complete induction level attained with water-soluble carcinogens that did not require metabolic activation. High sensitivity was achieved with the use of the lambda cIts857 prophage strain. In several instances where the Ames Salmonella-microsome test has failed to confirm the carcinogenicity of the respective carcinogens, this induction test has provided a better correlation. Of the carcinogens tested, only one false negative, namely, cyclophosphamide, was encountered. In contrast, the use of the wild-type prophage lambda strain resulted in low sensitivity. The adoption of the endolysin assay technique for the assessment of induction has greatly simplified the procedures and has permitted the screening test to be performed quickly and economically.

Bacteriophage lambda↗
PubMed1982

Properties of the N gene transcription antitermination protein of bacteriophage lambda.

The product of the N gene of bacteriophage lambda prevents the termination of lambda early transcription. Here we describe the physical properties of pure lambda N protein. N protein is small and very basic. The apparent Mr of N protein during electrophoresis in the presence of sodium dodecyl sulfate is 12,500. It contains 22 mol % (arginine plus lysine) and only one methionine. The methionine residue is at the blocked NH2 terminal since N protein is not detectably shortened by reaction with cyanogen bromide. When use is made of the DNA sequence of the N gene region of lambda DNA (Franklin, N. C., and Bennett, G. N. (1979) Gene 8, 107-119), the lack of an internal methionine residue, the size, and the amino acid composition of N protein can be used to predict that N protein contains 107 amino acids (calculated Mr = 12,241) and that its coding sequence begins at position 223 of the lambda pL operon mRNA. N protein can be assayed by its ability to stimulate endolysin synthesis in vitro in a reaction programmed with lambda N- DNA. N protein activity is heat-stable and trypsin-sensitive. Its sedimentation velocity in a sucrose gradient and its Stokes' radius indicate that N protein is an extremely asymmetric monomer (f/fmin = 1.6). The relationship between this high degree of molecular asymmetry and the sequence which N protein must recognize in lambda nucleic acid is discussed.

Amino Acids↗
PubMed1993

Characterization of PEA-15, a major substrate for protein kinase C in astrocytes.

Astrocytes in the central nervous system are involved in a variety of functions including storage of glycogen, maintenance of the extracellular ionic equilibrium, and support for the migration and the differentiation of neurons. Astrocytes express membrane receptors allowing them to respond to extracellular signals. Activation of receptors induces a cascade of events, such as stimulation of protein kinases and subsequent phosphorylation of target proteins. To understand the regulatory processes underlying neuroglial interactions, attempts were made to identify major phosphorylated proteins in striatal astrocytes, grown in primary culture and labeled with [32P]phosphate. Two-dimensional gel electrophoresis revealed a major doublet, Pa and Pb, of highly labeled spots, with a low molecular weight (M(r) = 15,000) and acidic pI (pI = 5.2 and 5.3, respectively). Using an enriched, heat-stable, cytosolic fraction, Pa and Pb were eluted from semi-preparative two-dimensional gels and subjected to a limited proteolysis and partial microsequencing. The same sequences were obtained within Pa and Pb and had no homology with other known protein. Antibodies raised against corresponding synthetic peptides confirm that the doublet represents two isoelectric variants of the same protein, which also exists under a nonphosphorylated form, N. We propose to name this protein PEA-15, for Phosphoprotein Enriched in Astrocytes-15 kDa, according to its large enrichment in these cells. Treatment of intact astrocytes with 12-O-tetradecanoylphorbol-13-acetate (TPA), which stimulates protein kinase C (PKC), increased the phosphorylation of the more acidic spot (Pb) while decreasing Pa intensity. Stimulations of astrocytes known to increase PKC activity, i.e. noradrenaline, or its inhibition by decreasing extracellular calcium concentrations, staurosporine, or desensitization following long term treatment with TPA, induced a phosphorylation or a dephosphorylation of PEA-15, respectively. Using purified PKC, PEA-15 appeared to be a good substrate in vitro. Two-dimensional peptide mapping revealed that the phosphorylation site in intact cells was identical with the site phosphorylated by PKC in vitro. Mapping the phosphopeptides by HPLC following endolysine C treatment lead to the identification of a sequence, phosphorylated in intact astrocytes and in vitro by PKC, containing a consensus site for PKC: LTRIPSAKK. Antibodies raised against a synthetic peptide derived from this sequence recognized N and Pa in control conditions and Pb after its dephosphorylation. Thus, PEA-15 is an endogenous substrate for PKC, the kinase mediating the transition from Pa to Pb.

Amino Acid Sequence↗
PubMed1977

[Functions of the late genes 13, 17, 18 and 19 in pi8 phage].

Genes of the right arm of the pi80 phage chromosome were characterized by studying lytic and antigenic activities and replication ability of mutant phages and by electron microscopic examination of their lysates. It is shown that the genes 14, 15 and 16 are early, and the genes 17, 18 and 19 are late. The functions of four genes are determined. The gene 13 is responsible for antigenic activity and for phage host-cell specificity; the gene 17 is a regulator of the late functions; the gene 18 product affects the cell membrane; the gene 19 controls the synthesis of phage endolysine. It is suggested to redesignate the pi80 phage genes 13, 17, 18 and 19 by the letters J, Q, S and R respectively, because these genes fulfil the same functions as the lambda genes J, Q, S and R.

Antigens, Viral↗
PubMed1998

The lambda holin accumulates beyond the lethal triggering concentration under hyperexpression conditions.

Most bacteriophages terminate infection by creating lesions in the cytoplasmic membrane, which not only cause immediate cell death but also allow escape of a phage-encoded endolysin. Destruction of the peptidoglycan and cell lysis follows very rapidly, allowing efficient release of the progeny virions. These membrane lesions are formed by a small integral membrane protein called a holin. Holins have highly charged carboxyl-termini that are thought to have two transmembrane alpha-helical domains. Holins are believed to oligomerize and form large holes in the inner membrane. The prototype holin is the S protein from bacteriophage lambda. Scheduling of the lytic event is determined in part by the "structure directed initiation" or sdi translational control region. Inductions of S, cloned under a variety of native and nonnative promoters but with native translational control, resulted in cell lysis at about 1000 molecules of holin per cell, and thus do not produce biochemically useful amounts of S protein. By utilizing a plasmid-based system with the T7 RNA polymerase promoter in tandem with a consensus ribosome binding site, Coomassie blue-detectable quantities of S protein were obtained upon induction, corresponding to an approximately 100-fold increase over the normal lethal level of holin. Characterization of this expression system is presented and discussed with respect to the current model of holin function.

Amino Acid Sequence↗