A phylogenetic analysis of the purple photosynthetic bacteria

It is proposed that gliding motility in bacteria is based on rotary assemblies located in the cell envelope and that these assemblies may be analogous to basal regions of bacterial flagella. This proposal rests on the following evidence: (i) Structures resembling flagellar basal regions have been demonstrated in cells ofCytophaga johnsonae andFlexibacter columnaris, and such structures are absent from one nonmotile mutant ofF. columnaris. (ii) The effects of inhibitors of energy metabolism on gliding motility are identical with their effects on prokaryotic fiagellar motility. (iii) The active movement of latex spheres along surfaces of gliding bacteria appears to depend on mechanisms responsible for motility and can be explained by the presence of rotary surface assemblies.     

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 9: comparison of acetoxy 4-methylcoumarins and other polyphenolic acetates reveal the specificity to acetoxy drug: protein transacetylase for pyran carbonyl group in proximity to the oxygen heteroatom

The evidences for the possible enzymatic transfer of acetyl groups (catalyzed by a transacetylase localized in microsomes) from an acetylated compound (acetoxy-4-methylcoumarins) to enzyme proteins leading to profound modulation of their catalytic activities was cited in our earlier publications in this series. The investigations on the specificity for transacetylase (TA) with respect to the number and positions of acetoxy groups on the benzenoid ring of coumarin molecule revealed that acetoxy groups in proximity to the oxygen heteroatom (at C-7 and C-8 positions) demonstrate a high degree of specificity to TA. These studies were extended to the action of TA on acetates of other polyphenols, such as flavonoids and catechin with a view to establish the importance of pyran carbonyl group for the catalytic activity. The absolute requirement of the carbonyl group in the pyran ring of the substrate for TA to function was established by the observation that TA activity was hardly discernible when catechin pentacetate and 7-acetoxy-3,4-dihydro-2,2-dimethylbenzopyran (both lacking pyran ring carbonyl group) were used as the substrates. Further, the TA activity with flavonoid acetates was remarkably lower than that with acetoxycoumarins, thus suggesting the specificity for pyran carbonyl group in proximity to the oxygen heteroatom. The biochemical properties of flavonoid acetates, such as irreversible activation of NADPH cytochrome C reductase and microsome-catalyzed aflatoxin B₁ binding to DNA in vitro were found to be in tune with their specificity to TA.     

The effect of elevated atmospheric CO2 and drought on sources and sinks of isoprene in a temperate and tropical rainforest mesocosm

Isoprene is the most abundant volatile hydrocarbon emitted by many tree species and has a major impact on tropospheric chemistry, leading to formation of pollutants and enhancing the lifetime of methane, a powerful greenhouse gas. Reliable estimates of global isoprene emission from different ecosystems demand a clear understanding of the processes of both production and consumption. Although the biochemistry of isoprene production has been studied extensively and environmental controls over its emission are relatively well known, the study of isoprene consumption in soil has been largely neglected. Here, we present results on the production and consumption of isoprene studied by measuring the following different components: (1) leaf and soil and (2) at the whole ecosystem level in two distinct enclosed ultraviolet light‐depleted mesocosms at the Biosphere 2 facility: a cottonwood plantation with trees grown at ambient and elevated atmospheric CO₂ concentrations and a tropical rainforest, under well watered and drought conditions. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter‐free soil of the agriforest stands showed no significant response to different CO₂ treatments, while isoprene production was strongly depressed by elevated atmospheric CO₂ concentrations. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. We conclude that soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget. More studies investigating the capacity of soils to uptake isoprene in natural conditions are clearly needed.     

The effect of elevated CO2 on diel leaf growth cycle, leaf carbohydrate content and canopy growth performance of Populus deltoides

Image sequence processing methods were applied to study the effect of elevated CO₂ on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO₂ for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO₂. Increased final leaf area at elevated CO₂ was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30–40% day^?1 was increased by a factor of two in the elevated CO₂ treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO₂ as the growing season progressed. During this minimum, leaves grown under elevated CO₂ decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO₂, suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO₂. Net CO₂ exchange and starch concentration of growing leaves was higher in elevated CO₂. The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO₂ is discussed.     

Quantitation of HLA proteins incorporated by human immunodeficiency virus type 1 and assessment of neutralizing activity of anti-HLA antibodies

Human anti-human leukocyte antigen (HLA) antibodies were assessed for neutralizing activity against human immunodeficiency virus type 1 (HIV-1) carrying HLA alleles with matching specificity. Multiparous women carrying anti-HLA antibodies were identified. Plasma samples from those women were confirmed as having antibodies that specifically bound to HLA proteins expressed on the peripheral blood mononuclear cells (PBMCs) of their husbands. A primary HIV-1 isolate was cultured in the husband's PBMCs so that the virus carried matching HLA alleles. To determine the HIV-1-neutralizing activity of anti-HLA antibodies, the infectivity of the virus for GHOST cells (which express green fluorescent protein after HIV infection) was investigated in the presence of a plasma sample positive for the respective anti-HLA antibody. A neutralization assay was also performed using purified immunoglobulin G (IgG) from two plasma samples, and two plasma samples were investigated in the presence of complement. The prerequisite for anti-HLA antibody-mediated neutralization is incorporation of HLA proteins by HIV-1. Therefore, the extent of incorporation of HLA proteins by the primary HIV-1 isolate was estimated. The ratios of HLA class I protein to HIV-1 capsid (p24) protein cultured in the PBMCs of two healthy individuals were 0.017 and 0.054. These ratios suggested that the HIV-1 strain used in the assay incorporated more HLA proteins than gp160 trimers. Anti-HLA antibody-positive plasma was found to contain antibodies that specifically reacted to HIV-1 carrying cognate HLA alleles. However, incubation of HIV-1 with anti-HLA antibody- positive plasma or purified IgG did not show a reduction in viral infectivity. HIV-1-neutralizing activity was also not detected in the presence of complement. This study shows that HIV-1 primary isolates cultured in PBMCs contain significant amounts of HLA proteins. However, the binding of antibodies to those HLA proteins does not mediate a reduction in viral infectivity.     

Kinetic analysis by real-time PCR of hepatitis C virus (HCV)-specific T cells in peripheral blood and liver after challenge with HCV

Intrahepatic virus-specific CD8(+) T cells are thought to be important for the control of hepatitis C virus (HCV) infection, yet the precise kinetics for the expansion of epitope-specific T cells over the course of infection are difficult to determine with currently available methods. We used a real-time PCR assay to measure the frequency of clonotypic HCV-specific CD8(+) T cells in peripheral blood and snap-frozen liver biopsy specimens of two chimpanzees (Pan troglodytes) with previously resolved HCV infection who were rechallenged with HCV. In response to rechallenge, the magnitude of each clonotypic response was 10-fold higher in the liver than in the blood, and the peak clonotype frequency was concurrent with the peak viral load. The higher frequency of HCV-specific clonotypes in the liver than in peripheral blood was maintained for at least 3 months after the clearance of viremia. After antibody-mediated CD8(+) T-cell depletion and another viral challenge, the rebound of these clonotypes was seen prior to an appreciable reconstitution of CD8(+) T-cell values and, again, at higher frequencies in the liver than in peripheral blood. These data demonstrate the importance of intrahepatic virus-specific CD8(+) T cells for the clearance of infection and the rapid kinetics of expansion after virus challenge.     

Cloning of an ovule specific promoter from Arabidopsis thaliana and expression of beta-glucuronidase

Tissue specific expression of transgenes in plant species has several advantages over constitutive expression. Identification of ovule specific promoters would be useful in genetic engineering of plants with a variety of desirable traits such as genetically engineered parthenocarpy, female sterile plants or seedless fruits. Relative inaccessibility and difficulty in harvesting adequate amounts of tissue at known developmental stages has impeded the progress in cloning of promoters involved in ovule development. In the present study an ovule specific promoter was cloned from Arabidopsis AGL11 gene and used to express GUS (beta-glucuronidase) gene in transgenic Arabidopsis. Histochemical staining of GUS appeared in the center of young ovary (ovules), but no detectable GUS activity was observed in vegetative plant tissues, sepals, petals and androecium. AGL11 gene promoter can be useful to modify the developmental path of plants by expressing either plant hormones or lethal genes for agronomic purpose.     

Functional characterization, localization, and molecular identification of rabbit intestinal N-amino acid transporter

We have characterized the Na-glutamine cotransporter in the rabbit intestinal crypt cell brush border membrane vesicles (BBMV). Substrate specificity experiments showed that crypt cell glutamine uptake is mediated by system N. Real-time PCR experiments showed that SN2 (SLC38A5) mRNA is more abundant in crypt cells compared with SN1 (SLC38A3), indicating that SN2 is the major glutamine transporter present in the apical membrane of the crypt cells. SN2 cDNA was obtained by screening a rabbit intestinal cDNA library with human SN1 used as probe. Rabbit SN2 cDNA encompassed a 473-amino-acid-long open reading frame. SN2 protein displayed 87% identity and 91% similarity to human SN2. Functional characterization studies of rabbit SN2 were performed by using vaccinia virus-mediated transient expression system. Substrate specificity of the cloned transporter was identical to that of SN2 described in the literature and matched well with substrate specificity experiments performed using crypt cell BBMV. Cloned rabbit SN2, analogous to its human counterpart, is Li(+) tolerant. Hill coefficient for Li(+) activation of rabbit SN2-mediated uptake was 1. Taken together, functional data from the crypt cell BBMV and the cloned SN2 cDNA indicate that the crypt cell glutamine transport is most likely mediated by SN2.