A gene coding for a thermostable nuclease was cloned from the thermophilic microorganism,
Thermusfiliformis (Tf), using an indicator strain containing a
dinD∷lacZ fusion. The gene, designated
nuc17, ...has been mapped within a 2300-bp fragment. The 55-kDa
Tf nuclease was purified to over 95% homogeneity. Single-stranded (ss) DNA is the preferred substrate for the
Tfnuclease, although double-stranded (ds) DNA can also be digested. Nuclease activity increases with increasing temperature up to 80°C and requires the metal ions Ca
+− or Mg
++for catalysis.
Tf nuclease is primarily an endonuclease that leaves 5′ phosphates in the digested products. The ssDNA extensions remaining after exonuclease III digestion of dsDNA can be removed by the
Tf nuclease, making it a useful reagent to generate unidirectional deletions.
Two heat-sensitive
R.BamHI mutants, T1571 and P173L, and one cold-sensitive
R.BamHI mutant, T1141, were isolated after chemical mutagenesis of the
bamhIR gene that codes for the restriction ...endonuclease
BamHI (R.BamHI). The thermosensitivity of T1141, T1571 and P173L is revealed by the 10
2−10
3 lower plating efficiency at the non-permissive temperature of strains bearing these alleles. The conditional-lethal phenotype can be rescued by introduction of the cognate
bamhIM gene into the same cell. The mutant enzymes induce the SOS response in vivo and display reduced phage restriction activity. The P173L protein, when expressed at 30°C and purified, shows reduced thermostability at 65°C. T1571 and P173L mutants yield different intermediates during partial trypsin digestion. The conditional-lethal
BamHI mutants could be used to deliver in vivo DNA cleavage and for further isolation of relaxed-specificity mutants.
A 1440-bp plasmid named pAP12875 was isolated from
Acetobacter pasteurianus and its nucleotide sequence determined. An open reading frame was found capable of coding for a protein that has similarity ...with the replication protein of pVT736-1 from
Actinobacillus actinomycetemcomitans and the 32-kDa protein of phage Pf3 from
Pseudomonas aeruginosa
Oxidation of nanosized titanium (nano-Ti), a promising component of energetic compounds, was studied using thermogravimetry and differential scanning calorimetry. To obtain more comprehensive insight ...into the kinetics and mechanism of oxidation, a variety of complementary non-isothermal and isothermal thermoanalytical experiments were performed. In sharp contrast to micron-sized titanium, oxidation of nano-Ti commences at much lower temperatures (150 °C instead of 650 °C) with profoundly lower activation energies (152 ± 3 kJ mol−1 and 220 ± 3 kJ mol−1, respectively). Moreover, reaction kinetics for nano-Ti obeys the logarithmic law, while in the case of micron-sized Ti kinetics is described by the 2D-diffusion model. At the microscopic level, the observed kinetics of nano-Ti oxidation is explained by switching of the limiting reaction stage to short-circuit diffusion of oxygen through the titanium oxide. This process is promoted by the increase of porosity upon initial water loss and the blocking of pores in the course of oxidation. The kinetic model proposed for oxidation of nano-Ti was independently benchmarked against the isothermal kinetics (zero heating rate limit) and ignition data (high heating rates). Our model provides reliable kinetics of the nano-Ti oxidation, which is valid for both storage and application conditions.
The synthesis of various polybenzimidazoles (PBIs) in condensation media such as polyphosphoric acid and Eaton’s reagent was accomplished. Molecular weight distribution of the synthesized polymers ...was examined with respect to the process conditions and the chemical structure of the monomers. It was found that during the synthesis of PBIs a side acylation reaction occurs which leads to the formation of branched macromolecules with Mw up to 2.3 × 106 and higher and even crosslinking, resulting in gelation of the polymers during synthesis. Fraction of the side reaction in the overall process appeared to be dependant on both the chemical structure of the monomers and the condensation media used. The orientation of the acylation reaction was determined by quantum-mechanical calculations.
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