Ozone production chemistry in the presence of urban plumes.

Ozone pollution affects human health, especially in urban areas on hot sunny days. Its basic photochemistry has been known for decades and yet it is still not possible to correctly predict the high ozone levels that are the greatest threat. The CalNex_SJV study in Bakersfield CA in May/June 2010 provided an opportunity to examine ozone photochemistry in an urban area surrounded by agriculture. The measurement suite included hydroxyl (OH), hydroperoxyl (HO2), and OH reactivity, which are compared with the output of a photochemical box model. While the agreement is generally within combined uncertainties, measured HO2 far exceeds modeled HO2 in NOx-rich plumes. OH production and loss do not balance as they should in the morning, and the ozone production calculated with measured HO2 is a decade greater than that calculated with modeled HO2 when NO levels are high. Calculated ozone production using measured HO2 is twice that using modeled HO2, but this difference in calculated ozone production has minimal impact on the assessment of NOx-sensitivity or VOC-sensitivity for midday ozone production. Evidence from this study indicates that this important discrepancy is not due to the HO2 measurement or to the sampling of transported plumes but instead to either emissions of unknown organic species that accompany the NO emissions or unknown photochemistry involving nitrogen oxides and hydrogen oxides, possibly the hypothesized reaction OH + NO + O2 → HO2 + NO2.

Impacts of Combustion Conditions and Photochemical Processing on the Light Absorption of Biomass Combustion Aerosol.

The aim was to identify relationships between combustion conditions, particle characteristics, and optical properties of fresh and photochemically processed emissions from biomass combustion. The combustion conditions included nominal and high burn rate operation and individual combustion phases from a conventional wood stove. Low temperature pyrolysis upon fuel addition resulted in "tar-ball" type particles dominated by organic aerosol with an absorption Ångström exponent (AAE) of 2.5-2.7 and estimated Brown Carbon contributions of 50-70% to absorption at the climate relevant aethalometer-wavelength (520 nm). High temperature combustion during the intermediate (flaming) phase was dominated by soot agglomerates with AAE 1.0-1.2 and 85-100% of absorption at 520 nm attributed to Black Carbon. Intense photochemical processing of high burn rate flaming combustion emissions in an oxidation flow reactor led to strong formation of Secondary Organic Aerosol, with no or weak absorption. PM1 mass emission factors (mg/kg) of fresh emissions were about an order of magnitude higher for low temperature pyrolysis compared to high temperature combustion. However, emission factors describing the absorption cross section emitted per kg of fuel consumed (m(2)/kg) were of similar magnitude at 520 nm for the diverse combustion conditions investigated in this study. These results provide a link between biomass combustion conditions, emitted particle types, and their optical properties in fresh and processed plumes which can be of value for source apportionment and balanced mitigation of biomass combustion emissions from a climate and health perspective.

Laboratory studies on secondary organic aerosol formation from crude oil vapors.

Airborne measurements of aerosol composition and gas phase compounds over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico in June 2010 indicated the presence of high concentrations of secondary organic aerosol (SOA) formed from organic compounds of intermediate volatility. In this work, we investigated SOA formation from South Louisiana crude oil vapors reacting with OH in a Potential Aerosol Mass flow reactor. We use the dependence of evaporation time on the saturation concentration (C*) of the SOA precursors to separate the contribution of species of different C* to total SOA formation. This study shows consistent results with those at the DWH oil spill: (1) organic compounds of intermediate volatility with C* = 10(5)-10(6) µg m(-3) contribute the large majority of SOA mass formed, and have much larger SOA yields (0.37 for C* = 10(5) and 0.21 for C* = 10(6) µg m(-3)) than more volatile compounds with C*≥10(7) µg m(-3), (2) the mass spectral signature of SOA formed from oxidation of the less volatile compounds in the reactor shows good agreement with that of SOA formed at DWH oil spill. These results also support the use of flow reactors simulating atmospheric SOA formation and aging.

Extreme oxidant amounts produced by lightning in storm clouds.

Lightning increases the atmosphere's ability to cleanse itself by producing nitric oxide (NO), leading to atmospheric chemistry that forms ozone (O3) and the atmosphere's primary oxidant, the hydroxyl radical (OH). Our analysis of a 2012 airborne study of deep convection and chemistry demonstrates that lightning also directly generates the oxidants OH and the hydroperoxyl radical (HO2). Extreme amounts of OH and HO2 were discovered and linked to visible flashes occurring in front of the aircraft and to subvisible discharges in electrified anvil regions. This enhanced OH and HO2 is orders of magnitude greater than any previous atmospheric observation. Lightning-generated OH in all storms happening at the same time globally can be responsible for a highly uncertain, but substantial, 2 to 16% of global atmospheric OH oxidation.

Free Radicals Within the Antarctic Vortex: The Role of CFCs in Antarctic Ozone Loss.

How strong is the case linking global release of chlorofluorocarbons to episodic disappearance of ozone from the Antarctic stratosphere each austral spring? Three lines of evidence defining a link are (i) observed containment in the vortex of ClO concentrations two orders of magnitude greater than normal levels; (ii) in situ observations obtained during ten high-altitude aircraft flights into the vortex as the ozone hole was forming that show a decrease in ozone concentrations as ClO concentrations increased; and (iii) a comparison between observed ozone loss rates and those predicted with the use of absolute concentrations of ClO and BrO, the rate-limiting radicals in an array of proposed catalytic cycles. Recent advances in our understanding of the kinetics, photochemistry, and structural details of key intermediates in these catalytic cycles as well as an improved absolute calibration for ClO and BrO concentrations at the temperatures and pressures encountered in the lower antarctic stratosphere have been essential for defining the link.

A ribonucleotide reductase homolog of cytomegalovirus and endothelial cell tropism.

Human cytomegalovirus infects vascular tissues and has been associated with atherogenesis and coronary restenosis. Although established laboratory strains of human cytomegalovirus have lost the ability to grow on vascular endothelial cells, laboratory strains of murine cytomegalovirus retain this ability. With the use of a forward-genetic procedure involving random transposon mutagenesis and rapid phenotypic screening, we identified a murine cytomegalovirus gene governing endothelial cell tropism. This gene, M45, shares sequence homology to ribonucleotide reductase genes. Endothelial cells infected with M45-mutant viruses rapidly undergo apoptosis, suggesting that a viral strategy to evade destruction by cellular apoptosis is indispensable for viral growth in endothelial cells.

In Situ Northern Mid-Latitude Observations of ClO, O3, and BrO in the Wintertime Lower Stratosphere.

In order to test photochemical theories linking chlorofluorocarbon derivatives to ozone(O(3)) depletion at high latitudes in the springtime, several related atmospheric species, including O(3), chlorine monoxide(ClO), and bromine monoxide (BrO) were measured in the lower stratosphere with instruments mounted on the NASA ER-2 aircraft on 13 February 1988. The flight path from Moffett Field, California (37 degrees N, 121 degrees W), to Great Slave Lake, Canada (61 degrees N, 115 degrees W), extended to the center of the polar jet associated with but outside of the Arctic vortex, in which the abundance of O(3) was twice its mid-latitude value, whereas BrO levels were 5 parts per trillion by volume (pptv) between 18 and 21 kilometers, and 2.4 pptv below that altitude. The ClO mixing ratio was as much as 65 pptv at 60 degrees N latitude at an altitude of 20 kilometers, and was enhanced over mid-latitude values by a factor of 3 to 5 at altitudes above 18 kilometers and by as much as a factor of 40 at altitudes below 17 kilometers. Levels of ClO and O(3) were highly correlated on all measured distance scales, and both showed an abrupt change in character at 54 degrees N latitude. The enhancement of ClO abundance north of 54 degrees N was most likely caused by low nitrogen dioxide levels in the flight path.

The potential for ozone depletion in the arctic polar stratosphere.

The nature of the Arctic polar stratosphere is observed to be similar in many respects to that of the Antarctic polar stratosphere, where an ozone hole has been identified. Most of the available chlorine (HCl and ClONO(2)) was converted by reactions on polar stratospheric clouds to reactive ClO and Cl(2)O(2) throughout the Arctic polar vortex before midwinter. Reactive nitrogen was converted to HNO(3), and some, with spatial inhomogeneity, fell out of the stratosphere. These chemical changes ensured characteristic ozone losses of 10 to 15% at altitudes inside the polar vortex where polar stratospheric clouds had occurred. These local losses can translate into 5 to 8% losses in the vertical column abundance of ozone. As the amount of stratospheric chlorine inevitably increases by 50% over the next two decades, ozone losses recognizable as an ozone hole may well appear.

Forward with BACs: new tools for herpesvirus genomics.

The large, complex genomes of herpesviruses document the high degree of adaptation of these viruses to their hosts. Not surprisingly, the methods developed over the past 30 years to analyse herpesvirus genomes have paralleled those used to investigate the genetics of eukaryotic cells. The recent use of bacterial artificial chromosome (BAC) technology in herpesvirus genetics has made their genomes accessible to the tools of bacterial genetics. This has opened up new avenues for reverse and forward genetics of this virus family in basic research, and also for vector and vaccine development.

Rapid identification of essential and nonessential herpesvirus genes by direct transposon mutagenesis.

Herpesviruses are important pathogens in animals and humans. The large DNA genomes of several herpesviruses have been sequenced, but the function of the majority of putative genes is elusive. Determining which genes are essential for their replication is important for identifying potential chemotherapy targets, designing herpesvirus vectors, and generating attenuated vaccines. For this purpose, we recently reported that herpesvirus genomes can be maintained as infectious bacterial artificial chromosomes (BAC) in Escherichia coli. Here we describe a one-step procedure for random-insertion mutagenesis of a herpesvirus BAC using a Tn1721-based transposon system. Transposon insertion sites were determined by direct sequencing, and infectious virus was recovered by transfecting cultured cells with the mutant genomes. Lethal mutations were rescued by cotransfecting cells containing noninfectious genomes with the corresponding wild-type subgenomic fragments. We also constructed revertant genomes by allelic exchange in bacteria. These methods, which are generally applicable to any cloned herpesvirus genome, will facilitate analysis of gene function for this virus family.

Immune evasion by cytomegalovirus--survival strategies of a highly adapted opportunist.

Slowly replicating, species-specific and complex DNA viruses, such as cytomegaloviruses (CMVs), which code for > 200 antigenic proteins, should be easy prey to the host's immune system. Yet, CMVs are amazingly adapted opportunists that cope with multiple immune responses. Frequently, CMVs exploit immune mechanisms generated by the host. These strategies secure the persistence of CMVs and provide opportunities to spread to naive individuals.

Epithelial differentiation fails to support replication of cloned human papillomavirus type 16 DNA in transfected keratinocytes.

Research on the life cycle of human papillomaviruses (HPVs) has suffered from the lack of a model system that allows the use of molecularly cloned HPV DNA. In this study, we analyzed replication of molecularly cloned HPV-16 genomes after transfection into cells of two human keratinocyte cell lines. Transfected cells were grown in cell culture (in vitro) or in transplantation chambers on the flanks of nude mice (in vivo). When DNA was extracted after different time intervals, replication of HPV-16 DNA could not be detected. Even the formation of a stratified epithelium under in vivo conditions failed to support vegetative replication. In contrast, transfection of molecularly cloned HPV-11 DNA resulted in replication of viral DNA in vitro. It seems likely that besides epithelial cell differentiation, a number of other factors influence HPV-16 replication.

Cytomegaloviruses inhibit Bak- and Bax-mediated apoptosis with two separate viral proteins.

Apoptosis of infected cells can limit virus replication and serves as an innate defense mechanism against viral infections. Consequently, viruses delay apoptosis by expressing antiapoptotic proteins, many of which structurally resemble the cellular antiapoptotic protein Bcl-2. Like Bcl-2, the viral analogs inhibit apoptosis by preventing activation and/or oligomerization of the proapoptotic mitochondrial proteins Bax and Bak. Here we show that cytomegaloviruses (CMVs) have adopted a different strategy. They encode two separate mitochondrial proteins that lack obvious sequence similarities to Bcl-2-family proteins and specifically counteract either Bax or Bak. We identified a small mitochondrion-localized protein encoded by the murine CMV open reading frame (ORF) m41.1, which functions as a viral inhibitor of Bak oligomerization (vIBO). It blocks Bak-mediated cytochrome c release and Bak-dependent induction of apoptosis. It protects cells from cell death-inducing stimuli together with the previously identified Bax-specific inhibitor viral mitochondria-localized inhibitor of apoptosis (vMIA) (encoded by ORF m38.5). Similar vIBO proteins are encoded by CMVs of rats, and possibly by other CMVs as well. These results suggest a non-redundant function of Bax and Bak during viral infection, and a benefit for CMVs derived from the ability to inhibit Bak and Bax separately with two viral proteins.

Persistent hyperinsulinaemic hypoglycaemia of infancy: therapy, clinical outcome and mutational analysis.

UNLABELLED: Persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI) is an autosomal recessive disorder characterized by irregular insulin secretion leading to hypoglycaemia. Recently, mutations in the sulphonylurea receptor (SUR) have been described in association with PHHI. We studied clinical symptoms, therapy, long-term outcome and mutational analysis in 14 patients with PHHI. In 8 patients subtotal pancreatectomy was performed whereas 6 responded to conservative treatment with diazoxide. Psychomotor retardation was found in 6 patients, most of them after a delayed diagnosis. A G-to-A point mutation in one allele of the SUR gene was detected by loss of a MspI restriction site in only one patient. CONCLUSION: Early diagnosis and therapy in PHHI is essential to prevent brain damage. In one patient mutational analysis suggested compound heterozygosity for a known and an as yet unidentified mutation in the SUR gene.

A mouse model for cytomegalovirus infection.

This unit describes procedures for infecting newborn and adult mice with murine cytomegalovirus (mCMV). Methods are included for propagating mCMV in cell cultures and for preparing a more virulent form of mCMV from salivary glands of infected mice. A plaque-forming cell (PFC) assay is provided for measuring mCMV titers of infected tissues or virus stocks. In addition, a method is described for preparing the murine embryonic fibroblasts used for propagating mCMV and for the PFC assay.

Secreted virus-encoded proteins reflect murine cytomegalovirus productivity in organs.

Mouse infection with murine cytomegalovirus (MCMV) is an established model for studying human cytomegalovirus infection. In this study, the relationship was analyzed between MCMV activity in organs of infected mice and the presence of infectious virus (viremia), viral genomes (DNAemia), or secreted virus-encoded proteins in the blood. For the latter, 2 recombinant viruses were constructed that encode for the hepatitis B virus surface antigen and the secreted alkaline phosphatase, respectively, as secreted marker proteins. The secreted markers correlated better with the infection in organs than DNAemia and viremia. The marker protein assays can serve as practical and sensitive tools for longitudinal monitoring of MCMV infection in individual mice.

Fast screening procedures for random transposon libraries of cloned herpesvirus genomes: mutational analysis of human cytomegalovirus envelope glycoprotein genes.

We have cloned the human cytomegalovirus (HCMV) genome as an infectious bacterial artificial chromosome (BAC) in Escherichia coli. Here, we have subjected the HCMV BAC to random transposon (Tn) mutagenesis using a Tn1721-derived insertion sequence and have provided the conditions for excision of the BAC cassette. We report on a fast and efficient screening procedure for a Tn insertion library. Bacterial clones containing randomly mutated full-length HCMV genomes were transferred into 96-well microtiter plates. A PCR screening method based on two Tn primers and one primer specific for the desired genomic position of the Tn insertion was established. Within three consecutive rounds of PCR a Tn insertion of interest can be assigned to a specific bacterial clone. We applied this method to retrieve mutants of HCMV envelope glycoprotein genes. To determine the infectivities of the mutant HCMV genomes, the DNA of the identified BACs was transfected into permissive fibroblasts. In contrast to BACs with mutations in the genes coding for gB, gH, gL, and gM, which did not yield infectious virus, BACs with disruptions of open reading frame UL4 (gp48) or UL74 (gO) were viable, although gO-deficient viruses showed a severe growth deficit. Thus, gO (UL74), a component of the glycoprotein complex III, is dispensable for viral growth. We conclude that our approach of PCR screening for Tn insertions will greatly facilitate the functional analysis of herpesvirus genomes.

Novel GLRA1 missense mutation (P250T) in dominant hyperekplexia defines an intracellular determinant of glycine receptor channel gating.

Missense mutations as well as a null allele of the human glycine receptor alpha1 subunit gene GLRA1 result in the neurological disorder hyperekplexia [startle disease, stiff baby syndrome, Mendelian Inheritance in Man (MIM) #149400]. In a pedigree showing dominant transmission of hyperekplexia, we identified a novel point mutation C1128A of GLRA1. This mutation encodes an amino acid substitution (P250T) in the cytoplasmic loop linking transmembrane regions M1 and M2 of the mature alpha1 polypeptide. After recombinant expression, homomeric alpha1(P250T) subunit channels showed a strong reduction of maximum whole-cell chloride currents and an altered desensitization, consistent with a prolonged recovery from desensitization. Apparent glycine binding was less affected, yielding an approximately fivefold increase in Ki values. Topological analysis predicts that the substitution of proline 250 leads to the loss of an angular polypeptide structure, thereby destabilizing open channel conformations. Thus, the novel GLRA1 mutant allele P250T defines an intracellular determinant of glycine receptor channel gating.

A GLRA1 null mutation in recessive hyperekplexia challenges the functional role of glycine receptors.

Dominant missense mutations in the human glycine receptor (GlyR) alpha 1 subunit gene (GLRA1) give rise to hereditary hyperekplexia. These mutations impair agonist affinities and change conductance states of expressed mutant channels, resulting in a partial loss of function. In a recessive case of hyperekplexia, we found a deletion of exons 1-6 of the GLRA1 gene. Born to consanguineous parents, the affected child is homozygous for this GLRA1(null) allele consistent with a complete loss of gene function. The child displayed exaggerated startle responses and pronounced head-retraction jerks reflecting a disinhibition of vestigial brain-stem reflexes. In contrast, proprio- and exteroceptive inhibition of muscle activity previously correlated to glycinergic mechanisms were not affected. This case demonstrates that, in contrast to the lethal effect of a null allele in the recessive mouse mutant oscillator (Glra1 spd-ot), the loss of the GlyR alpha 1 subunit is effectively compensated in man.