Specificity of mutations induced by riboflavin mediated photosensitization in the supF gene of Escherichia coli

Riboflavin-mediated photosensitization has been shown to produce 8-hydroxyguanine (oh8Gua) in DNA. We investigated the specificity of mutation of photosensitized supF gene induced in Escherichia coli. The oh8Gua repair deficient E. coli mutant mutM and mutY were transformed with plasmid pUB3 carrying the supF gene irradiated with white light in the presence of riboflavin. Under these conditions, riboflavin photosensitization increased the amounts of oh8Gua in pUB3 DNA. Three types of a single base substitution occurring at G:C pairs were detected in both wild-type and mutM mutant strains. Almost all base substitutions were transversions to T:A or C:G pairs occurring at a similar extent in both wild-type and mutM strains. Mutations derived from mutY strain transformed with photosensitized DNA were only G:C to T:A transversions. These G:C to T:A transversions observed in the mutY strain were suggested to be the result of mispairing of oh8Gua with adenine. Riboflavin-mediated photosensitization may also produce lesions on DNA causing G:C to C:G changes by unknown mechanisms.     

Role of macrophages in acute murine cytomegalovirus infection

It has been recognized that macrophages play an important role in controlling virus infection in experimental animal models. To evaluate the role of macrophages in acute murine cytomegalovirus infection, macrophages in the spleen and the liver were eliminated by an intravenous injection of liposomes containing a cytolytic agent, dichloromethylene diphosphonate. The depletion of macrophages led to a significant increase of virus titer in the spleen and lungs in both susceptible BALB/c and resistant C57BL/6 mice during the first three days after intravenous infection. In the spleen, the increase of virus titer in macrophage-depleted BALB/c mice was much greater than that in NK cell-depleted mice. These results suggest that macrophages contribute to protection mainly by the mechanisms which are independent of NK cells during the first three days after infection. The increase of virus titer in macrophage-depleted C57BL/6 mice was as great as that in NK cell-depleted mice because of the high contribution of NK cells to protection in C57BL/6 mice. In the liver in both strains of mice, the effects of macrophage depletion on virus titer were not as much as those in the spleen and lungs. Furthermore, the local depletion of peritoneal macrophages resulted in a great increase of virus titer in the spleen at three days after intraperitoneal infection. We conclude that macrophages greatly contribute to decreasing the virus load in some organs possibly through either or both intrinsic and extrinsic mechanisms in the early phase of primary infection with murine cytomegalovirus.     

Rescue of angiotensinogen-knockout mice

Angiotensinogen, the precursor of angiotensins I and II, is a critical component of the renin-angiotensin system that plays an important role in regulating blood pressure and electrolyte homeostasis. Genetically altered mice lacking angiotensinogen (Agt-KO) showed an expected phenotype, such as marked hypotension, but unexpected ones including abnormal kidney morphology, reduced survival rates of newborns, and impaired blood-brain barrier function after cold injury. To examine whether disruption of the angiotensinogen gene is responsible for the observed phenotypes, we generated a line of mice heterozygous for the mouse angiotensinogen gene under the control of a mouse metallothionein-I promoter (MT-Agt) and crossmated transgenic mice with Agt-KO mice. The resulting mice (MT-Agt(+/-)/Agt(-/-):MT-Agt/KO) produced the plasma level of angiotensin I comparable to that of wild-type mice, and the mutant phenotypes were rescued. These results indicated that the resultant phenotypes due to the genetic deficiency of mouse angiotensinogen can be corrected by restoring angiotensinogen and angiotensin I in the circulation.     

Anthropogenic Pu distribution in Tropical East Pacific

The geographical distribution of the anthropogenic radionuclides ²³⁸Pu and ^239 + 240Pu in the Tropical East Pacific in 2003 was studied from the viewpoint of material migration. We measured the contents of Pu isotopes in seawater and in sediment from the sea bottom. The distributions of Pu isotopes, together with those of coexisting nitrate and phosphate species and dissolved oxygen, are discussed in relation to the potential temperature and potential density (sigma-θ). The Pu contents in sediment samples were compared with those in the seawater. Horizontal migration across the Equator from north to south was investigated at depths down to ~ 800 m in the eastern Pacific. The Pu distribution at 0-400 m correlated well with the distribution of potential temperature. Maximum Pu levels were observed in the subsurface layer at 600-800 m, corresponding to the depth where sigma-θ ≈ 27.0. It is suggested that the Pu distribution depends on the structure of the water mass and the particular temperature and salinity. The water column/sediment column inventory ratio and the vertical distribution of Pu may reflect the efficiency of scavenging in the relevant water areas.     

Molecular modelling of entanglement

The modelling of molecular entanglement in polymeric materials is an old problem, and has evolved gradually over the last 60 years, with two key approaches: the network model of Green & Tobolsky, and the tube model of Edwards and de Gennes. We will show that these models can be merged together in a straightforward manner. The resulting model, called the dual slip-link model, can be handled by computer simulation, and it can predict the linear and nonlinear rheological behaviours of linear and star polymers with arbitrary molecular weight distribution.     

Elongational viscosities of random and block copolymer melts

The influence of random and block copolymerized structures on the uniaxial elongational viscosity was investigated. The investigated random copolymers were poly(ethylene-random-ethyl methacrylate) with comb-branched structure and poly(styrene-random-acrylonitrile) with linear structure. The studied block copolymers were poly(styrene-block-ethylenebutylene-block-styrene) with linear structure. The elongational viscosities of random copolymers showed strain-hardening properties. The strain-hardening property was influenced little by comonomer contents and depended on whether copolymers had linear or branched structures. In contrast, the elongational viscosities of block copolymers gave strain-softening properties. The strain-softening property was not affected by strain rates and block comonomer ratios. The causes of strain-hardening and -softening properties are discussed from relaxation spectrum and damping function based on the Bernstein–Kearsley–Zapas model. The damping functions of linear and branched random copolymers agreed with those of linear and branched homopolymers, respectively. On the other hand, linear block copolymers exhibited stronger damping than linear homopolymers. It was concluded that strain-hardening and -softening properties in the elongational viscosity of random and block copolymerized structures are correlated with their damping functions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1765–1774, 1998     

Value-utilized taint propagation: toward precise detection of apps’ information flows across Android API calls

International Journal of Information Security - Android security researchers utilize taint analysis to uncover apps’ bugs and policy-violating behaviors. However, the investigations are...     

Physical aging and thermal aging resistance of polycarbonate/poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) blends

The effect of thermal annealing on the mechanical properties of polycarbonate (PC) was investigated by tensile testing, Izod impact testing, and differential scanning calorimetry (DSC). An endothermic peak appeared in the DSC curve by annealing at various temperatures below T_g. The peak area, as a measure of the degree of physical aging, increased with annealing time. The Izod impact strength decreased suddenly just before an endothermic peak became detectable. The results imply that at the very early stage of physical aging, a trigger for the ductile‐to‐brittle transition may be initiated. By blending hydrogenated styrene‐butadiene‐styrene block copolymer (SEBS), the embrittlement by annealing was prevented. That is, in the PC/SEBS blends, the physical aging of PC matrix proceeded in the same way as in neat PC; however, the Izod impact strength did not decrease. This thermal aging resistance seems to originate from the negative pressure effect of SEBS particles that provides dilational stress fields for PC matrix to enhance the local segment motions. POLYM. ENG. SCI., 52:1958–1963, 2012. © 2012 Society of Plastics Engineers