Inactivation of de novo DNA methyltransferase activity by high concentrations of double-stranded DNA

The activity of eukaryotic DNA methyltransferase diminishes with time when the enzyme is incubated with high concentrations (200–300 μg/ml) of unmethylated double-stranded Micrococcus luteus DNA. Under similar conditions, single-stranded DNA induces only a limited decrease of enzyme activity. The inactivation process is apparently due to a slowly progressive interaction of the enzyme with double-stranded DNA that is independent of the presence of S-adenosyl-l-methionine. The inhibited enzyme cannot be reactivated either by high salt dissociation of the DNA-enzyme complex or by extensive digestion of the DNA. Among synthetic polydeoxyribonucleotides both poly(dG-dC) · poly(dG-dC) and poly(dA-dT) · poly(dA-dT), but not poly(dI-dC) · poly(dI-dC), cause inactivation of DNA methyltransferase. This inactivation process may be of interest in regulating the ‘de novo’ activity of the enzyme.     

Inactivation of de novo DNA methyltransferase activity by high concentrations of double-stranded DNA

The activity of eukaryotic DNA methyltransferase diminishes with time when the enzyme is incubated with high concentrations (200-300 micrograms/ml) of unmethylated double-stranded Micrococcus luteus DNA. Under similar conditions, single-stranded DNA induces only a limited decrease of enzyme activity. The inactivation process is apparently due to a slowly progressive interaction of the enzyme with double-stranded DNA that is independent of the presence of S-adenosyl-L-methionine. The inhibited enzyme cannot be reactivated either by high salt dissociation of the DNA-enzyme complex or by extensive digestion of the DNA. Among synthetic polydeoxyribonucleotides both poly(dG-dC).poly(dG-dC) and poly(dA-dT).poly(dA-dT), but not poly(dI-dC).poly(dI-dC), cause inactivation of DNA methyltransferase. This inactivation process may be of interest in regulating the 'de novo' activity of the enzyme.     

Identification of thermophilic bacteria in solid-waste composting

The thermophilic microbiota of solid-waste composting, with major emphasis on Bacillus spp., was examined with Trypticase soy broth (BBL Microbiology Systems) with 2% agar as the initial plating medium. Five 4.5-liter laboratory units at 49 to 69 degrees C were fed a mixture of dried table scraps and shredded newspaper. The composting plants treating refuse at Altoona, Pa., and refuse-sludge at Leicester, England, were also sampled. Of 652 randomly picked colonies, 87% were identified as Bacillus spp. Other isolates included two genera of unidentified nonsporeforming bacteria (one of gram-negative small rods and the other of gram-variable coccobacilli), the actinomycetes Streptomyces spp. and Thermoactinomyces sp., and the fungus Aspergillus fumigatus. Among the Bacillus isolates, the following, in order of decreasing frequency, were observed: B. circulans complex, B. stearothermophilus, B. coagulans types A and B, B. licheniformis, B. brevis, B. sphaericus, Bacillus spp. types i and ii, and B. subtilis. About 15% of the Bacillus isolates could be assigned to species only by allowing for greater variability in one or more characteristics than has been reported by other authors for their strains. In particular, growth at higher temperatures than previously reported was found for strains of several species. A small number of Bacillus isolates (less than 2%) could not be assigned to any recognized species.     

Dual parameter flow cytometric analysis of DNA content, activation antigen expression, and T cell subset proliferation in the human mixed lymphocyte reaction

This study provides direct correlation via dual parameter flow cytometry (simultaneous assessment of immunofluorescence and DNA content) between mixed lymphocyte reaction (MLR) responder cell entry into the S/G2/M phases of the cell cycle with the kinetics of expression of two activation-associated cell surface proteins, Tac (IL 2 receptor) and 4F2 (unknown metabolic function). A small population of activated cells was identifiable by expression of both Tac and 4F2 antigens before peak DNA synthesis in the MLR. This population of activation antigen-positive cells expanded linearly in size from days 3 to 7 of culture. Treatment of immature MLR cultures with anti-4F2 Mab and complement (C) before DNA synthesis (treatment on day 3, peak DNA synthesis on days 5 to 6) resulted in blunted proliferation and activation antigen expression when the same culture was analyzed after maturation on day 6, indicating that the activated population had been previously detected and removed by anti-4F2 Mab + C. The 4F2 antigen was expressed on a greater percentage of cells in the MLR at all times (days 3 to 9) than was Tac, was present on virtually all S/G2/M phase responder cells, and a large fraction of cells remained intensely 4F2+ subsequent to peak DNA synthesis. In contrast, after initially preceding responder cell entry into the S phase of the cell cycle, the kinetics of Tac antigen expression closely paralleled the kinetics of responder cell proliferation. A subpopulation of cycling responder cells was noted in all MLR cultures studied that expressed Tac antigen weakly or not at all. Cells within both T4 and T8 cell subsets proliferate with similar kinetics in response to alloantigen. The possibility that activation antigens can be utilized to study effector cell generation in the MLR and that this flow cytometric technique may be utilized to analyze the response to various alloantigens is discussed.     

Repair of Alkylated Bacteriophage T4 Deoxyribonucleic Acid by a Mechanism Involving Polynucleotide Ligase

Methyl methanesulfate-induced lesions in bacteriophage T4 are repaired primarily by a mechanism involving polynucleotide ligase. Apparently, other recombinational and ultraviolet repair functions aren't involved.     

Segregation analysis of cancer in families of childhood soft-tissue-sarcoma patients.

This paper presents the analysis of familial cancer data collected in a hospital-based study of 159 childhood soft-tissue-sarcoma patients. Two different statistical models detected excess aggregation of cancer, which could be explained by a rare dominant gene. For each kindred, we estimated the probability of the observed cancer distribution under the dominant-gene model and identified 12 families that are the most likely to be segregating the gene. Two of those families have confirmed germ-line mutations in the p53 tumor-suppressor gene. The relative risk of affection for children who are gene carriers was estimated to be 100 times the background rate. Females were found to have a slightly higher age-specific penetrance, but maternal and paternal lineages made equal contributions to the evidence in favor of the dominant gene. The proband's histology, ethnicity, and age at diagnosis were evaluated to determine whether any of these altered the probability of affection in family members. Only embryonal rhabdomyosarcoma was found to be a significant covariate under the dominant-gene model. While molecular genetic studies of familial cancer will eventually provide answers to the questions of genetic heterogeneity, age- and site-specific penetrance, mutation rates, and gene frequency, information from statistical models is useful for setting priorities and defining hypotheses.     

Cloning of an Aeromonas hydrophila type IV pilus biogenesis gene cluster: complementation of pilus assembly functions and characterization of a type IV leader peptidase/N-methyltransferase required for extracellular protein secretion

Aeromonas hydrophila secretes several extracellular proteins that are associated with virulence including an enterotoxin, a protease, and the hole-forming toxin, aerolysin. These degradative enzymes and toxins are exported by a conserved pathway found in many Gram-negative bacteria. In Pseudomonas aeruginosa this export pathway and type IV pilus biogenesis are dependent on the product of the pilD gene. PilD is a bifunctional enzyme that processes components of the extracellular secretory pathway as well as a type IV prepilin. An A. hydrophila genomic library was transferred into a P. aeruginosa pilD mutant that is defective for type IV pilus biogenesis. The A. hydrophila pilD homologue, tapD , was identified by its ability to complement the pilD mutation in P. aeruginosa . Transconjugants containing tapD were sensitive to the type IV pilus-specific phage, PO4. Sequence data revealed that tapD is part of a cluster of genes ( tapABCD ) that are homologous to P. aeruginosa type IV pilus biogenesis genes ( pilABCD ). We showed that TapB and TapC are functionally homologous to P. aeruginosa PilB and PilC, the first such functional complementation of pilus assembly demonstrated between bacteria that express type IV pili. In vitro studies revealed that TapD has both endopeptidase and N -methyltransferase activities using P. aeruginosa prepilin as substrate. Furthermore, we show that tapD is required for extracellular secretion of aerolysin and protease, indicating that tapD may play an important role in the virulence of A. hydrophila