Accurate knowledge of the electron density structure of the Earth's upper atmosphere is crucial to forecasting the performance of transionospheric radio signals. For this research, we focus on storm-time structuring in the mid- to high latitude ionosphere where large gradients in electron density can cause severe degradation of communication and navigation signals. We begin in Chapter 2 with a review of the primary data sets and methods used to accomplish the collaborative, multi-instrument studies described in this dissertation. In Chapter 3, we compare observational techniques for tracking polar cap patches during a moderate geomagnetic storm interval. For the first time, we monitor the transportation of patches with high spatial and temporal resolution across the polar cap for 1--2~h using a combination of GPS TEC, all-sky airglow imagers (ASIs), and Super Dual Auroral Radar Network (SuperDARN) HF radar backscatter. Simultaneous measurements from these data sets allow for continuous tracking of patch location, horizontal extent, and velocity even under adverse observational conditions for one or more of the techniques. A focus is placed on the structuring of patches, particularly on the nightside ionosphere as they become wider in the dawn-dusk direction and develop narrow finger-like structures. In Chapter 4, we perform a superposed epoch analysis to characterize the average response of GPS TEC in the North American sector during more than 100 geomagnetic storms over a 13-year interval. For the first time a rigorous approach is used to fully separate storm-time, local time, longitudinal, and seasonal effects at midlatitudes where dense ground receiver coverage is available. The rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer-lasting negative phase across all latitudes and local times. Our results show clear seasonal variations in the storm-time TEC, such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects. A prominent magnetic declination effect is identified and examined in terms of thermospheric zonal winds pushing plasma upward/downward along magnetic field lines of opposite declination. Finally in Chapter 5 we summarize several co-authored studies which examined various storm-time phenomena utilizing GPS TEC mapping tools developed for this dissertation research, with topics including subauroral polarization stream (SAPS), storm enhanced density (SED), tongue of ionization (TOI), and polar cap patches. / Ph. D.

No / The growth of crystals of a-resorcinol from the vapor phase is asymmetric along the polar axis. By means of molecular-dynamics simulations, the slower growth at the (011) polar surface is traced back to conformational change of the molecule and to surface reconstruction, which may be a general phenomenon in polar crystals.

Considerando germes de hipersuperfícies em \'C POT.n+1\' com conjunto singular de dimensão s, Massey em [14] introduz um conjunto de (s+1) números chamados de números de Lê. Estes números se mostram como a generalização natural do número de Milnor para singularidades isoladas. O principal objetivo deste trabalho é mostrar como estes números são obtidos e que os números de Lê de uma hipersuperfície singular estão relacionados com os números de Lê de uma certa sequência de hipersuperfícies singulares \'X IND.0\',...,\'X IND.s-1\' que se aproxima da singularidade original de tal forma que os conjuntos críticos de seus termos \'X IND.i\' têm dimensão i. Essas relações são dadas pelas fórmulas de Lê-Iomdine. / For any germ of hypersurface in \'C POT. n+1\' with singular set of dimension s, Massey in [14] introduces a set of (s+1) numbers called Lê numbers. These numbers are a natural generalization of the Milnor number for isolated singularity hypersurfaces. The main goal of this work is to show how to obtain these numbers and to show the Lê numbers of a singular hypersurface are related with the the Lê numbers of a sequence of singular hypersurfaces \'X IND.0\',...,\'X IND.s-1\' which approach the original singularity in such a way that the critical set of each \'X IND.i\' has dimension i. These relationship are given by the Lê-Iomdine formulas.

A constante exposição dos diferentes organismos a agentes que danificam a estrutura da molécula do DNA fez com que a célula desenvolvesse mecanismos de reparo que se mostraram conservados durante a evolução. Em células de mamíferos, as vias de reparo ao dano ao DNA e a regulação dos pontos de checagem do ciclo celular atuam de forma coordenada no reparo do dano a fim de evitar uma progressão do ciclo celular antes do reparo e uma possível perpetuação do dano. Além disso, alguns dos componentes dessas vias metabólicas também atuam em outros processos, como replicação, transcrição, recombinação meiótica e silenciamento gênico. NER é um importante mecanismo no processo que reconhece e remove dímeros de ciclobutano e 6-4 pirimidina-pirimidona da estrutura do DNA. Em mamíferos foram identificados sete grupos de complementação para células deficientes de XP (XPA-G). Um desses grupos é XPE, conhecido por possuir forte afinidade ao dano ao DNA causado por luz UV, sendo formado por duas subunidades, DDB1 e DDB2. Uma busca no banco de dados de Aspergillus nidulans utilizando uma seqüência DDB1 de Homo sapiens, revelou uma única seqüência com similaridade relevante denominada como DdbA que não possui nenhuma similaridade com a proteína DDB2. Em Aspergillus nidulans, a proteína DdbA também está envolvida no reparo do dano ao DNA causado por luz UV e 4-NQO, no entanto, vimos aqui, que DdbA está interagindo com as proteínas UvsBATR, H2AX e CshBCSB no reparo ao dano ao DNA causado por MMS, Bleomicina, 4-NQO e luz UV. Além disso, uma análise na expressão do gene ddbA mostrou que ele é induzido por estas drogas, no estresse oxidativo e nos processos de desenvolvimento assexual e sexual de A. nidulans. Nós também vimos que a localização celular de DdbA não foi afetada durante a resposta ao dano ao DNA causado por luz UV e 4-NQO indicando que a proteína DdbA está presente no núcleo independentemente do dano. Em S. pombe, as proteínas serina-treonina quinases CHK1 e CHK2 foram identificadas como essenciais para o bloqueio do ciclo celular na fase S em resposta ao dano ao DNA ou em resposta ao estresse replicacional. Essas quinases são fosforiladas pelas quinases ATM e ATR e tem sido extensivamente caracterizadas em A. nidulans. Neste fungo, as proteínas ChkACHK1 e ChkBCHK2 estão envolvidas na reposta ao dano ao DNA e estão interagindo de forma epistática e sinergística com as proteínas quinases AtmAATM e UvsBATR. Nossos resultados também sugerem que as proteínas ChkA e ChkB podem estar envolvidas em meiose, e atuam em vias complementares durante o bloqueio da fase S do ciclo celular. Além disso, as proteínas AtmA, ChkA, ChkB e UvsB são redundantemente complementares na manutenção do crescimento polar das hifas em Aspergillus nidulans. / The constant exposure of different organisms to agents that damage the DNA structure, has provided the cells with repair mechanisms that are conserved during evolution. In mammal cells, the DNA damage repair pathways and the cell cycle checkpoint regulation act together to prevent cell cycle progression before the repair is performed avoiding mutation fixaxion. However these responses are complex and demand overlapping functions and the intersection of many metabolic pathways. NER is an important mechanism in the process that recognize and remove cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidone photoproduct from the DNA structure. In mammals seven complementation groups for XP deficient cells were identified. One of these groups is XPE, known for having strong affinity to the DNA damage caused by UV light and is formed by two subunits DDB1 and DDB2. A search on the Aspergilus nidulans database using a Homo sapiens DDB1 sequence, revealed a single ORF with relevant similarity. The A. nidulans homologue was deleted and named DdbA. ddbA does not have significant similarity to DDB2 protein. In A. nidulans the protein DdbA is involved on the DNA damage repair caused by UV light and 4NQO. Additionaly ddbA is genetically interacting with uvsBATR, histone H2AX and cshBCSB the damage repair caused by MMS , BLEO, 4NQO and UV light. Also, an analysis of the gene ddbA expression indicated that it is induced by MMS, BLEO, 4-NQO, oxidative stressing agents and by the assexual and sexual development processes of A. nidulans. We also verified that the sub-cellular localization of DdbA was not affected by the presence of UV light or 4-NQO indicating that the protein DdbA is constitutively present in the nucleus. In S. pombe, the serine treonine kinases CHK1 and CHK2 proteins were identified as essential to the Sphase blockage in response to the DNA damage or replicational stress. These kinases are phosphorilated by ATR and ATM kinases, respectively and have been extensively characterized in A. nidulans. In this fungus, the proteins ChkACHK1 and ChkBCHK2 are involved on the DNA damage response and are genetically interacting in an epistatic and/or synergistic manner with the AtmAATM and UvsBATR kinases. Our results also sugest that the proteins ChkA and ChkB may also be involved in meiosis and act in a complementary way during the S-phase block. Furthermore the AtmA, ChkA, ChkB e UvsB proteins are complementary redundant for the maintenance of the polar growth in A. nidulans.

Considerando germes de hipersuperfícies em \'C POT.n+1\' com conjunto singular de dimensão s, Massey em [14] introduz um conjunto de (s+1) números chamados de números de Lê. Estes números se mostram como a generalização natural do número de Milnor para singularidades isoladas. O principal objetivo deste trabalho é mostrar como estes números são obtidos e que os números de Lê de uma hipersuperfície singular estão relacionados com os números de Lê de uma certa sequência de hipersuperfícies singulares \'X IND.0\',...,\'X IND.s-1\' que se aproxima da singularidade original de tal forma que os conjuntos críticos de seus termos \'X IND.i\' têm dimensão i. Essas relações são dadas pelas fórmulas de Lê-Iomdine. / For any germ of hypersurface in \'C POT. n+1\' with singular set of dimension s, Massey in [14] introduces a set of (s+1) numbers called Lê numbers. These numbers are a natural generalization of the Milnor number for isolated singularity hypersurfaces. The main goal of this work is to show how to obtain these numbers and to show the Lê numbers of a singular hypersurface are related with the the Lê numbers of a sequence of singular hypersurfaces \'X IND.0\',...,\'X IND.s-1\' which approach the original singularity in such a way that the critical set of each \'X IND.i\' has dimension i. These relationship are given by the Lê-Iomdine formulas.

This study examined the differences in the chemical composition, particularly fatty acids, of the lipid extracted from the fibre of bucks, does and castrated goats. The study provides a more detailed understanding of the chemical composition of buck fibre lipid and how it varies throughout the year, and also details the effect of body region and nutrition on the production and chemical composition of lipid from buck fibre. Lipid was extracted with either petroleum ether (non-polar) or chloroform/methanol azeotrope (polar) and analysed by gas chromatography and gas chromatography-mass spectrometry. The more polar solvent system extracted larger amounts of lipid and more of each individual fatty acid. The following buck specific ethyl branched fatty acids were identified: 2-ethylhexanoic, 4-ethylhexanoic, 2-ethyloctanoic, 4-ethyloctanoic, 6-ethyloctanoic, 2-ethyldecanoic, 4-ethyldecanoic, 2-ethyldodecanoic, 6-ethyldodecanoic, 4-ethyldodecanoic, 2-ethyltetradecanoic, 6-ethyltetradecanoic, 4-ethyltetradecanoic, 2-ethylhexadecanoic and 4-ethyloctadecanoic acids. Of these buck specific fatty acids only 4-ethylhexanoic (T), 4-ethyloctanoic, 4-ethyldecanoic, 4-ethyldodecanoic, 6-ethyldodecanoic (T), 4-ethyltetradecanoic, 2-ethylhexadecanoic (T) and 4-ethylhexadecanoic acids have been previously identified or tentatively identified (T) in buck fibre extracts. This shows that the chemical composition of buck fibre lipid is more complex than previously reported, and that it may be more difficult than previously thought to artificially duplicate the odour of the buck. Buck fibre samples had lower average concentrations of 2-methylpropanoic, 2-methylbutanoic, iso-pentadecanoic, anteiso-pentadecanoic, iso-hexadecanoic, anteiso-heptadecanoic, iso-octadecanoic and anteiso-nonadecanoic acids as compared with fibre samples from does, spayed does, or wethers that were castrated at one month of age. The reduced concentrations of these fatty acids in buck fibre extracts were likely to be due to the synthesis of ethyl branched derivatives of iso and anteiso fatty acids. Buck fibre samples had higher concentrations of benzoic acid as compared with fibre samples from does, spayed does, or wethers that were castrated at one month of age. The significance of these results is that non buck specific fatty acids may also make a contribution to the odour of bucks. When fibre samples were collected at various times throughout the year, it was found that the bucks had increased amounts of lipid and ethyl branched fatty acids in fibre samples shorn from March to September, as compared with fibre samples shorn in November and January. The increase in the amount of lipid and ethyl branched fatty acids corresponded with both the rutting period of the buck and the period when the buck odour was increased. This suggests that ethyl branched fatty acids could be pheromones. The variation in lipid content and fatty acid composition was also examined between fibre samples collected from different body regions of the buck during April, as alterations in sebaceous gland activity around the neck during rutting have been reported. It was found that the average amount of lipid in the neck region of the bucks was not statistically higher than the average amounts in the midside and hind regions. However, the ethyl branched fatty acid concentrations were statistically higher in the fibre from around the neck as compared with the fibre from the other body regions, which is consistent with the odour of the buck being most pronounced around the head and neck region. The lipid content and composition of fibre samples from bucks fed high and low quality diets (lucerne and pangola grass, respectively) was examined to determine the effect of nutrition on buck specific components. The high quality diet increased the amount of lipid and ethyl branched fatty acids in fibre samples collected in April from the neck, midside and hind regions, as compared with fibre samples from the corresponding body regions from bucks fed the low quality diet. Thus it may be possible for the pheromone levels of bucks to be increased by simply providing them with good nutrition. The lipid content and ethyl branched fatty acid concentrations of fibre samples increased earlier in the year for the lucerne fed bucks as compared with the pangola grass fed bucks. The lucerne fed bucks had increased concentrations of ethyl branched fatty acids in fibre samples shorn during December to June (6 months) whereas the pangola grass fed bucks had increased concentrations of ethyl branched fatty acids in fibre samples shorn during April to August (4 months). These observations show that good nutrition can result in both the earlier production of ethyl branched fatty acids and an extended period when ethyl branched fatty acids are produced. This suggests that nutrition can be used to manipulate pheromone levels in the buck. The period when the ethyl branched fatty acids were increased corresponded with the period when the plasma luteinizing hormone (LH) and testosterone concentrations, odour and sebaceous gland volume of the bucks were increased, which supports the assumption that ethyl branched fatty acids are involved in odour production and act as pheromones.

Die Residualzirkulation entspricht der mittleren Massenzirkulation und beschreibt die im zonalen Mittel stattfindenden meridionalen Transportprozesse. Die Variationen der Residualzirkulation bestimmen gemeinsam mit dem anthropogen verursachten Ozonabbau die jährlichen Schwankungen der Ozongesamtsäule im arktischen Frühling. In der vorliegenden Arbeit wird die Geschwindigkeit des arktischen Astes der Residualzirkulation aus atmosphärischen Daten gewonnen. Zu diesem Zweck wird das diabatische Absinken im Polarwirbel mit Hilfe von Trajektorienrechnungen bestimmt. Die vertikalen Bewegungen der Luftpakete können mit vertikalen Windfeldern oder entsprechend einem neuen Ansatz mit diabatischen Heizraten angetrieben werden. Die Eingabedaten stammen aus dem 45 Jahre langen Reanalyse-Datensatz des "European Centre for Medium Range Weather Forecast" (ECMWF). Außerdem kann für die Jahre ab 1984 die operationelle ECMWF-Analyse verwendet werden. Die Qualität und Robustheit der Heizraten- und Trajektorienrechnungen werden durch Sensitivitätsstudien und Vergleiche mit anderen Modellen untermauert. Anschließend werden umfangreiche Trajektorienensemble statistisch ausgewertet, um ein detailliertes, zeit- und höhenaufgelöstes Bild des diabatischen Absinkens zu ermitteln. In diesem Zusammenhang werden zwei Methoden entwickelt, um das Absinken gemittelt im Polarwirbel oder als Funktion der äquivalenten Breite zu bestimmen. Es wird gezeigt, dass es notwendig ist den Lagrangeschen auf Trajektorienrechnungen basierenden Ansatz zu verfolgen, da die einfachen Eulerschen Mittel Abweichungen zu den Lagrangeschen Vertikalgeschwindigkeiten aufweisen. Das wirbelgemittelte Absinken wird für einzelne Winter mit dem beobachteten Absinken langlebiger Spurengase und anderen Modellstudien verglichen. Der Vergleich zeigt, dass das Absinken basierend auf den vertikalen Windfeldern der ECMWF-Datensätze den Nettoluftmassentransport durch die Residualzirkulation sehr stark überschätzt. Der neue Ansatz basierend auf den Heizraten ergibt hingegen realistische Ergebnisse und wird aus diesem Grund für alle Rechnungen verwendet. Es wird erstmalig eine Klimatologie des diabatischen Absinkens über einen fast fünf Jahrzehnte umfassenden Zeitraum erstellt. Die Klimatologie beinhaltet das vertikal und zeitlich aufgelöste diabatische Absinken gemittelt über den gesamten Polarwirbel und Informationen über die räumliche Struktur des vertikalen Absinkens. Die natürliche Jahr-zu-Jahr Variabilität des diabatischen Absinkens ist sehr stark ausgeprägt. Es wird gezeigt, dass zwischen der ECMWF-Zeitreihe des diabatischen Absinkens und der Zeitreihe aus einem unabhängig analysierten Temperaturdatensatz hohe Korrelationen bestehen. Erstmals wird der Einfluss von Transportprozessen auf die Ozongesamtsäule im arktischen Frühling direkt quantifiziert. Es wird gezeigt, dass die Jahr-zu-Jahr Variabilität der Ozongesamtsäule im arktischen Frühling zu gleichen Anteilen durch die Variabilität der dynamischen Komponente und durch die Variabilität der chemischen Komponente beeinflusst wird. Die gefundenen Variabilitäten von diabatischem Absinken und Ozoneintrag in hohen Breiten werden mit der vertikalen Ausbreitung planetarer Wellen aus der Troposphäre in die Stratosphäre in Beziehung gesetzt. / Due to the variability of tropospheric wave activity, the strength of the residual circulation has a distinct seasonal cycle and significant year-to-year variability. The variability of the residual circulation causes interannual variations of the polar ozone layer in late winter and spring. A reverse domain filling trajectory model based on atmospheric data sets is used to calculate the strength and spatial structure of the polar branch of the residual circulation. The atmospheric data sets (ERA-40 and ECMWF Analysis) emerge from a combined analysis of Reanalysis data and a weather forecast model and are available for a time period of 47 years starting from September 1957. Two different approaches are used in the trajectory routine to calculate the vertical movement of air. The first approach is based on the vertical velocity given by "European Centre for Medium Range Weather Forecast" (ECMWF), a quantity that is derived from the divergence of the horizontal winds and that tends to be noisy. In the second approach a radiation transfer model is used to calculate the diabatic heating rates from the divergence of the net radiation flux. The derived descent from both methods is compared with measured tracer distributions from satellite data and Arctic field campaigns. The comparison shows that the second approach results in a much more realistic vertical transport. The method based on the diabatic heating rates is used to compile a climatology of the diabatic descent, averaged within the polar vortex for the Arctic winters 1957/58-2003/04. Furthermore, the climatology contains information regarding the spatial structure of the diabatic descent. The influence of the diabatic descent in the Arctic polar vortex on the total ozone column is calculated for the recent winters since 1990. It is shown that the interannual variability of the Arctic total ozone column is in equal shares caused by dynamical transport processes and by chemical ozone depletion.

The goal of this research was to investigate further the role of air redistribution and continental water storage changes in the excitation of both the annual and Chandler wobbles for the period 1900-85. The annual and Chandler excitations from air redistribution have been studied by Wilson and Haubrich (1976), Wahr (1982), and Hinnov and Wilson (1985). Annual excitation from water storage was estimated by Van Hylckama (1970), Hinnov and Wilson (1985), and Chao and O'Connor (1988). Chandler wobble excitation from water storage changes has been addressed only by Hinnov and Wilson (1985). This study was undertaken as a refinement to their encouraging but preliminary results. / text

The definition of polar codes given by Arikan is explicit, but the construction complexity is an issue. This is due to the exponential growth in the size of the output alphabet of the bit-channels as the codeword length increases. Tal and Vardy recently presented a method for constructing polar codes which controls this growth. They approximated each bit-channel with a “better” channel and a “worse” channel while reducing the alphabet size. They constructed a polar code based on the “worse” channel and used the “better” channel to measure the distance from the optimal channel. This thesis considers the knowledge gained from the perspective of the “better” channel. A method is presented using iterative upgrading of the bit-channels which successively results in a channel closer to the original one. It is shown that this approach can be used to obtain a channel arbitrarily close to the original channel, and therefore to the optimal construction of a polar code. / Graduate / 0984 / 0544 / arash.ghayoori@gmail.com

A constante exposição dos diferentes organismos a agentes que danificam a estrutura da molécula do DNA fez com que a célula desenvolvesse mecanismos de reparo que se mostraram conservados durante a evolução. Em células de mamíferos, as vias de reparo ao dano ao DNA e a regulação dos pontos de checagem do ciclo celular atuam de forma coordenada no reparo do dano a fim de evitar uma progressão do ciclo celular antes do reparo e uma possível perpetuação do dano. Além disso, alguns dos componentes dessas vias metabólicas também atuam em outros processos, como replicação, transcrição, recombinação meiótica e silenciamento gênico. NER é um importante mecanismo no processo que reconhece e remove dímeros de ciclobutano e 6-4 pirimidina-pirimidona da estrutura do DNA. Em mamíferos foram identificados sete grupos de complementação para células deficientes de XP (XPA-G). Um desses grupos é XPE, conhecido por possuir forte afinidade ao dano ao DNA causado por luz UV, sendo formado por duas subunidades, DDB1 e DDB2. Uma busca no banco de dados de Aspergillus nidulans utilizando uma seqüência DDB1 de Homo sapiens, revelou uma única seqüência com similaridade relevante denominada como DdbA que não possui nenhuma similaridade com a proteína DDB2. Em Aspergillus nidulans, a proteína DdbA também está envolvida no reparo do dano ao DNA causado por luz UV e 4-NQO, no entanto, vimos aqui, que DdbA está interagindo com as proteínas UvsBATR, H2AX e CshBCSB no reparo ao dano ao DNA causado por MMS, Bleomicina, 4-NQO e luz UV. Além disso, uma análise na expressão do gene ddbA mostrou que ele é induzido por estas drogas, no estresse oxidativo e nos processos de desenvolvimento assexual e sexual de A. nidulans. Nós também vimos que a localização celular de DdbA não foi afetada durante a resposta ao dano ao DNA causado por luz UV e 4-NQO indicando que a proteína DdbA está presente no núcleo independentemente do dano. Em S. pombe, as proteínas serina-treonina quinases CHK1 e CHK2 foram identificadas como essenciais para o bloqueio do ciclo celular na fase S em resposta ao dano ao DNA ou em resposta ao estresse replicacional. Essas quinases são fosforiladas pelas quinases ATM e ATR e tem sido extensivamente caracterizadas em A. nidulans. Neste fungo, as proteínas ChkACHK1 e ChkBCHK2 estão envolvidas na reposta ao dano ao DNA e estão interagindo de forma epistática e sinergística com as proteínas quinases AtmAATM e UvsBATR. Nossos resultados também sugerem que as proteínas ChkA e ChkB podem estar envolvidas em meiose, e atuam em vias complementares durante o bloqueio da fase S do ciclo celular. Além disso, as proteínas AtmA, ChkA, ChkB e UvsB são redundantemente complementares na manutenção do crescimento polar das hifas em Aspergillus nidulans. / The constant exposure of different organisms to agents that damage the DNA structure, has provided the cells with repair mechanisms that are conserved during evolution. In mammal cells, the DNA damage repair pathways and the cell cycle checkpoint regulation act together to prevent cell cycle progression before the repair is performed avoiding mutation fixaxion. However these responses are complex and demand overlapping functions and the intersection of many metabolic pathways. NER is an important mechanism in the process that recognize and remove cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidone photoproduct from the DNA structure. In mammals seven complementation groups for XP deficient cells were identified. One of these groups is XPE, known for having strong affinity to the DNA damage caused by UV light and is formed by two subunits DDB1 and DDB2. A search on the Aspergilus nidulans database using a Homo sapiens DDB1 sequence, revealed a single ORF with relevant similarity. The A. nidulans homologue was deleted and named DdbA. ddbA does not have significant similarity to DDB2 protein. In A. nidulans the protein DdbA is involved on the DNA damage repair caused by UV light and 4NQO. Additionaly ddbA is genetically interacting with uvsBATR, histone H2AX and cshBCSB the damage repair caused by MMS , BLEO, 4NQO and UV light. Also, an analysis of the gene ddbA expression indicated that it is induced by MMS, BLEO, 4-NQO, oxidative stressing agents and by the assexual and sexual development processes of A. nidulans. We also verified that the sub-cellular localization of DdbA was not affected by the presence of UV light or 4-NQO indicating that the protein DdbA is constitutively present in the nucleus. In S. pombe, the serine treonine kinases CHK1 and CHK2 proteins were identified as essential to the Sphase blockage in response to the DNA damage or replicational stress. These kinases are phosphorilated by ATR and ATM kinases, respectively and have been extensively characterized in A. nidulans. In this fungus, the proteins ChkACHK1 and ChkBCHK2 are involved on the DNA damage response and are genetically interacting in an epistatic and/or synergistic manner with the AtmAATM and UvsBATR kinases. Our results also sugest that the proteins ChkA and ChkB may also be involved in meiosis and act in a complementary way during the S-phase block. Furthermore the AtmA, ChkA, ChkB e UvsB proteins are complementary redundant for the maintenance of the polar growth in A. nidulans.