FORMAÇÃO DE PROFESSORES(AS) E RELAÇÕES INTERPESSOAIS: UM ESTUDO EM SÃO BERNARDO DO CAMPO

Este trabalho investiga as relações interpessoais entre professores(as) e formadores(as), tendo como foco o(a) Professor(a) de Apoio Pedagógico (PAP), na Prefeitura de São Bernardo do Campo. Analisa a complexidade que envolve o trabalho formativo e verifica as relações estabelecidas entre estes pares: hierarquia, intervenções formativas, relações de poder, trabalho coletivo e veiculações de conhecimento. O(a) PAP ao final do ano é avaliado(a), num passado recente, pelo grupo, e atualmente, pelo(a) diretor(a) e referendado a assumir a função no ano seguinte, dando continuidade ao seu trabalho ou não. Se não referendado, volta para a sala de aula. Observa-se que alguns(mas) PAP s vem conseguindo ser referendados(as) e mantém-se há dez anos na função. A questão desta pesquisa é: O que leva o(a) formador(a) de professores(as) a conseguir tal legitimidade do grupo? Foram realizadas entrevistas, com vistas a uma abordagem metodológica de Histórias de Vida com análise das trajetórias formativas e profissionais de sete PAP´s (três que estão na função desde 1998, quando da sua criação, e quatro que estão na função desde 2007). Os referenciais teóricos estão ancorados em Antònio Nóvoa quando discute identidade e autoconhecimento do(a) professor(a); Paulo Freire na abordagem sobre dialogicidade como prática da liberdade; Madalena Freire quando analisa a resistência e constituição de grupo. A conclusão da pesquisa aponta que para conquistar a legitimidade do grupo, o(a) formador(a) deve estar atento para não cair na armadilha da burocracia, a qual por muitos anos tem feito parte das instituições escolares, promovendo enquadramento e controle; também não deve se aprisionar na arrogância que a posição gestora pode suscitar. Para conquistar a legitimidade do grupo, a capacidade de enfrentamento dos medos e conflitos através do diálogo como prática da liberdade é fundamental e, neste sentido, construir uma identidade formadora da qual faz parte o ouvir atento e o observar apurado dos movimentos do grupo, demanda uma postura ética em que as relações se constroem através do respeito, amorosidade, fé nos homens e criticidade.(AU)

EDUCAÇÃO MUSICAL: UM ESTUDO A PARTIR DOS PCN-ARTE E DA PERSPECTIVA DE PROFESSORES POLIVALENTES DO ENSINO FUNDAMENTAL

A fruição artística por meio da música é um modo privilegiado de conhecimento e aproximação entre indivíduos de culturas distintas. A música pode enriquecer o trabalho pedagógico, facilitando a compreensão dos fatos históricos e atuando na formação de sujeitos críticos e conscientes, agentes de seu próprio conhecimento, em um plano que vai além do discurso verbal. A área de música tem uma função importante a cumprir. A música situa o fazer artístico do homem histórico brasileiro, que conhece suas características tanto particulares, tal como se mostram na criação de uma arte brasileira, quanto universais, tal como se revelam no ponto de encontro do fazer dos artistas de todos os tempos, que sempre inauguram formas de tornar o presente explicável. Pode-se concluir da importância da música na prática escolar, que deve ter espaço garantido nas políticas educacionais. O objetivo desta pesquisa, nessa perspectiva, é verificar as recomendações dos Parâmetros Curriculares Nacionais (PCN-Arte) fazem quanto ao estudo da música e em que medida tais recomendações se expressam na prática educacional de escolas de Ensino Fundamental. Para tanto, explora-se, como referencial teórico escolhido, os estudos de Montanari (1988) e Barbosa (1983). É uma pesquisa de natureza qualitativa e se desenvolve por meio de estudos bibliográficos relacionados à temática, incluindo o PCN-Arte, e também da coleta de dados entre professores polivalentes. Os dados obtidos são objeto de análise de conteúdo, de acordo com as orientações de Szymanski, Almeida & Prandini (2004), sendo que as categorias examinadas emergiram dos depoimentos dos entrevistados. O estudo enfatiza o quanto é preciso avançar nas políticas educacionais em nosso País.

Luz e vida: uma proposta de formação continuada de professores

The Course “Light and Life”, which is a product of the present research, is a mediator in helping Science Teachers on how to deal with the Physics classes in secondary school. The aim of the present study was to propose a course which can help Science Teachers with their difficulties in the teaching of Physics in the later years of secondary school, mainly about topics related to the theme Light. The elaboration of the product of this research involved structuring and applying a course of continued formation through the “Fun with Science and Art Museum-DICA, under the theme Light, to Science Teachers of the later years of secondary school, in order to promote an environment of dialogue and problem raising as means of disseminating and discussing the teaching of topics related to Light in the teaching of Sciences. The formation course presented a flexible structure in order to widen the relation between the researcher and the teachers participating in the course, aiming to give an answer to the formative needs of the teachers in relation to the theme proposed. In order to know and discuss the problems and challenges of the teaching of Physics in the Science classes, an approach of insertion and integration of concepts related to the theme Light was conducted, mainly on topics relating to the contents of Physics, Chemistry and Biology, according to the curriculum and the abilities of Sciences worked on in class, through the approach of concepts and practice which approximate the practical and theoretical reality of the formative needs of the teachers involved in this study. This work aimed to understand the relation of Science Teachers with the theme Light and comprehend the relation of the teachers with the present proposal of continued formation promoted by the Museum DICA. The methodological option of this research remained in the domains of qualitative research whose analysis was based on the content analysis. The data collection was carried out through questionnaires and group discussions recorded in audio, besides the participative observation of the researcher. As the research product, the structuring and application of a course of continued formation of Science Teachers of secondary school was proposed, under the thematic Light, and a later restructuring of the course under the same thematic based on the data collected after the application of the referred course, which will be later promoted by the Museum DICA.

Rifting process and formation mechanisms of syn-rift stage prolongation in the deepwater basin, northern South China Sea

Based on the latest seismic and geological data, tectonic subsidence of three seismic lines in the deepwater area of Pearl River Mouth Basin (PRMB), the northern South China Sea (SCS), is calculated. The result shows that the rifting process of study area is different from the typical passive continental margin basin. Although the seafloor spreading of SCS initiated at 32 Ma, the tectonic subsidence rate does not decrease but increases instead, and then decreases at about 23 Ma, which indicates that the rifting continued after the onset of seafloor spreading until about 23 Ma. The formation thickness exhibits the same phenomenon, that is the syn-rift stage prolonged and the post-rift thermal subsidence delayed. The formation mechanisms are supposed to be three: (1) the lithospheric rigidity of the northern SCS is weak and its ductility is relatively strong, which delayed the strain relaxation resulting from the seafloor spreading; (2) the differential layered independent extension of the lithosphere may be one reason for the delay of post-rift stage; and (3) the southward transition of SCS spreading ridge during 24 to 21 Ma and the corresponding acceleration of seafloor spreading rate then triggered the initiation of large-scale thermal subsidence in the study area at about 23 Ma.

A new approach for multi-agent coalition formation and management in the scope of electricity markets

This paper presents a new methodology for the creation and management of coalitions in Electricity Markets. This approach is tested using the multi-agent market simulator MASCEM, taking advantage of its ability to provide the means to model and simulate VPP (Virtual Power Producers). VPPs are represented as coalitions of agents, with the capability of negotiating both in the market, and internally, with their members, in order to combine and manage their individual specific characteristics and goals, with the strategy and objectives of the VPP itself. The new features include the development of particular individual facilitators to manage the communications amongst the members of each coalition independently from the rest of the simulation, and also the mechanisms for the classification of the agents that are candidates to join the coalition. In addition, a global study on the results of the Iberian Electricity Market is performed, to compare and analyze different approaches for defining consistent and adequate strategies to integrate into the agents of MASCEM. This, combined with the application of learning and prediction techniques provide the agents with the ability to learn and adapt themselves, by adjusting their actions to the continued evolving states of the world they are playing in.

Sedimentology and stratigraphy of the Lower Silurian Grimsby formation, in subsurface, Lake Erie and Southwestern Ontario

Since the first offshore Lake Erie well was drilled in 1941, the Grimsby and Thorold formations of the Cataract Group have been economically important to the oil and gas industry of Ontario. The Cataract Group provides a significant amount of Ontario's gas production primarily from wells located on Lake Erie. The Grimsby - Thorold formations are the result of nearshore estuarine processes influenced by tides on a prograding shelf and are composed of subtidal channel complexes, discrete tidal channels, mud flats and non-marine deposits. Deposition was related to a regressive - transgressive cycle associated with eustatic sea level changes caused by the melting and resurgence of continental glaciation centred in Africa in the Late Ordovician/Early Silurian. Grimsby deposition began during a regression with the deposition of subtidal channel complexes incised into the marine deposits of the Cabot Head Formation. The presence of mud drapes and mud couplets suggest that these deposits were influenced by tides. These deposits dominate the lower half of the Grimsby. Deposition continued with a change from these subtidal channel complexes to laterally migrating, discrete, shallow tidal channels and mud flats. These were in turn overlain by the non-marine deposits of the Thorold Formation. Grimsby - Thorold deposition ended with a major transgression replacing siliciclastic deposition with primarily carbonate deposition. Sediment was sourced from the east and southeast and associated with a continuation of the Taconic Orogeny into the Early Silurian. The fluvial head of the estuary prograded from a shoreline that was located in western New York and western Pennsylvania running NNE-SSW and then turning NW-SE and paralleling the present day Lake Erie shoreline. iii The facies attributed to the Grimsby - Thorold formations can be ascribed to the three zones within the tripartite zonation suggested by Dalrymple et ale (1992) for estuaries, that is, a marine-dominated facies, a mixed energy facies, and a facies that is dominated by fluvial processes. Also, sediments within the Grimsby - Thorold are commonly fining upwards sequences which are common in estuarine settings whereas deltaic deposits are normally composed of coarsening upwards sequences in a vertical wedge shape with coarser material near the head. The only coarsening observed was in the Thorold Formation and attributed to non-marine deposition by palynological evidence. The presence of a lag deposit at the base of the sediments of the Grimsby Thorold formations suggests that they were incised into the Cabot Head Formation. Further, the thickness of Early Silurian sediments located between the top of the Queenston Formation, where Early Silurian sedimentation began, to the top of the Reynales - Irondequoit formation are constant whether the Grimsby - Thorold formations are present or not. Also, cross-sections using a sand body located in the Cabot Head Formation for correlation further imply that the Grimsby Formation has been incised into the previous deposits of the Cabot Head.

Fondements épistémologiques et représentations sociales d’enseignants d’histoire du secondaire à l’égard de l’enseignement de l’histoire et de la formation citoyenne

Cette thèse s’intéresse aux fondements épistémologiques et à la vision que des enseignants d’histoire au secondaire entretiennent à l’égard de l’enseignement de l’histoire et de la formation citoyenne. La réflexion s’inscrit dans le contexte de la refonte des programmes d’enseignement de l’histoire qui engage dorénavant les maîtres d’histoire à éduquer à la citoyenneté démocratique. Ce projet éducationnel repose sur le postulat suivant : l’apprentissage de l’histoire, de sa pensée et de sa méthode permet de former des individus capables de réflexion critique autonome et informée. Cette vision de l’enseignement de l’histoire implique que les élèves s’exercent à la pensée historienne, à l’analyse des sources et à la construction d’interprétations historiques. Ce faisant, ils développeraient une compréhension du monde fondée sur la maîtrise de concepts et une pensée complexe, ce qui servirait de ce fait la citoyenneté. La recherche a par ailleurs démontré que les maîtres avaient recours à des méthodes pédagogiques plus traditionnelles (Charland, 2003; Martineau, 1997). C’est donc à des changements de pratiques qu’appelle le ministère de l’Éducation. Or un tel changement ne se déclare pas « d’en haut ». Les convictions des maîtres sont lentes à se transformer et ce sont elles qui déterminent la formation historienne et citoyenne que recevront les élèves. Nous en avons fait notre objet d’étude pour cette recherche en recourant à la théorie des représentations sociales. Nous avons adopté le modèle du noyau central (Abric, 1994) et celui des principes organisateurs qui permet d’identifier les relations existantes entre plusieurs représentations. Nous avons effectué une recherche exploratoire de type qualitative. Des entretiens individuels semi-dirigés d’une durée moyenne de 120 minutes ont été réalisés avec un échantillon comptant 18 enseignants d’histoire au secondaire de Montréal, de Québec et de communautés amérindiennes du Québec. L’outil de cueillette et d’analyse des données s’inspire grandement des développements méthodologiques réalisés par la recherche sur les représentations sociales (évocation hiérarchisée continuée ou limitée, schémas conceptuels) (Abric, 1994; 1997). Les résultats permettent d’identifier les fondements épistémologiques et didactiques, le contenu et la structure, de même que les relations existant entre les représentations de l’enseignement de l’histoire et de la formation à la citoyenneté. Ils ont également mis en lumière les convictions idéologiques et pédagogiques des maîtres d’histoire.

Retroviral transfer of the p16INK4a cDNA inhibits C6 glioma formation in Wistar rats

Abstract Background The p16INK4A gene product halts cell proliferation by preventing phosphorylation of the Rb protein. The p16INK4a gene is often deleted in human glioblastoma multiforme, contributing to unchecked Rb phosphorylation and rapid cell division. We show here that transduction of the human p16INK4a cDNA using the pCL retroviral system is an efficient means of stopping the proliferation of the rat-derrived glioma cell line, C6, both in tissue culture and in an animal model. C6 cells were transduced with pCL retrovirus encoding the p16INK4a, p53, or Rb genes. These cells were analyzed by a colony formation assay. Expression of p16INK4a was confirmed by immunohistochemistry and Western blot analysis. The altered morphology of the p16-expressing cells was further characterized by the senescence-associated β-galactosidase assay. C6 cells infected ex vivo were implanted by stereotaxic injection in order to assess tumor formation. Results The p16INK4a gene arrested C6 cells more efficiently than either p53 or Rb. Continued studies with the p16INK4a gene revealed that a large portion of infected cells expressed the p16INK4a protein and the morphology of these cells was altered. The enlarged, flat, and bi-polar shape indicated a senescence-like state, confirmed by the senescence-associated β-galactosidase assay. The animal model revealed that cells infected with the pCLp16 virus did not form tumors. Conclusion Our results show that retrovirus mediated transfer of p16INK4a halts glioma formation in a rat model. These results corroborate the idea that retrovirus-mediated transfer of the p16INK4a gene may be an effective means to arrest human glioma and glioblastoma.

Rat lungs show a biphasic formation of new alveoli during postnatal development

Roughly 90% of the gas-exchange surface is formed by alveolarization of the lungs. To the best of our knowledge, the formation of new alveoli has been followed in rats only by means of morphological description or interpretation of semiquantitative data until now. Therefore, we estimated the number of alveoli in rat lungs between postnatal days 4 and 60 by unambiguously counting the alveolar openings. We observed a bulk formation of new alveoli between days 4 and 21 (17.4 times increase from 0.8 to 14.3 millions) and a second phase of continued alveolarization between days 21 and 60 (1.3 times increase to 19.3 million). The (number weighted) mean volume of the alveoli decreases during the phase of bulk alveolarization from ∼593,000 μm(3) at day 4 to ∼141,000 μm(3) at day 21, but increases again to ∼298,000 μm(3) at day 60. We conclude that the "bulk alveolarization" correlates with the mechanism of classical alveolarization (alveolarization before the microvascular maturation is completed) and that the "continued alveolarization" follows three proposed mechanisms of late alveolarization (alveolarization after microvascular maturation). The biphasic pattern is more evident for the increase in alveolar number than for the formation of new alveolar septa (estimated as the length of the free septal edge). Furthermore, a striking negative correlation between the estimated alveolar size and published data on retention of nanoparticles was detected.

Bioresorbable vascular scaffold treatment induces the formation of neointimal cap that seals the underlying plaque without compromising the luminal dimensions: a concept based on serial optical coherence tomography data.

Aims: To evaluate the implications of an Absorb bioresorbable vascular scaffold (Absorb BVS) on the morphology of the superficial plaques. Methods and results: Forty-six patients who underwent Absorb BVS implantation and 20 patients implanted with bare metal stents (BMS) who had serial optical coherence tomographic examination at baseline and follow-up were included in this analysis. The thin-capped fibroatheromas (TCFA) were identified in the device implantation regions and in the adjacent native coronary segments. Within all regions, circumferential locations of TCFA and calcific tissues were identified, and the neointimal thickness was measured at follow-up. At six to 12-month follow-up, only 8% of the TCFA detected at baseline were still present in the Absorb BVS and 27% in the BMS implantation segment (p=0.231). Sixty percent of the TCFA in native segments did not change their phenotype at follow-up. At short-term follow-up, significant reduction in the lumen area of the BMS was noted, which was higher compared to that reported in the Absorb BVS group (-2.11±1.97 mm2 vs. -1.34±0.99 mm2, p=0.026). In Absorb BVS, neointima tissue continued to develop at midterm follow-up (2.17±0.48 mm2 vs. 1.38±0.52 mm2, p<0.0001) and covered the underlying tissues without compromising the luminal dimensions (5.93±1.49 mm2 vs. 6.14±1.49 mm2, p=0.571) as it was accommodated by the expanded scaffold (8.28±1.74 mm2 vs. 7.67±1.28 mm2, p<0.0001). Conclusions: Neointimal tissue develops following either Absorb BVS or BMS implantation and shields lipid tissues. The neointimal response in the BMS causes a higher reduction of luminal dimensions compared to the Absorb BVS. Thus, Absorb BVS may have a value in the invasive re-capping of high-risk plaques.

The Role of EphA4 in Glial Scar Formation Following Injury

Although many areas of the brain lose their regenerative capacity with age, stem cell niches have been identified in both the subventricular zone (SVZ) along the lateral walls of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus (Gage, 2000; Alvarez-Buylla et al., 2001; Alvarez-Buylla and Lim, 2004). The SVZ niche utilizes many mechanisms to determine the migration patterns of neuroblasts along the RMS into the olfactory bulb, one being Eph/ephrin signaling (Conover et al., 2000; Holmberg et al., 2005). EphA4-mediated signaling is necessary for axon guidance during development, and its continued expression in the SVZ niche suggests a regulatory role throughout adulthood. Previous studies have suggested that EphA4 plays a role in the regulation of astrocytic gliosis and glial scar formation, which inhibits axonal regeneration in these areas following spinal cord injury (Goldshmit et al., 2004). Blood vessels may also play an important role in SVZ cell proliferation and neuroblast migration following injury (Tavazoie et al., 2008; Yamashita et al., 2006). The goal of this project is to examine glial scar formation as well as the relationship between SVZ vasculature, neuroblasts, and neural stem cells in EphA4 +/+, EphA4 +/-, and EphA4 -/- mice following a needle stick injury in the cortex or striatum. The outcome of these experiments will determine whether invasive procedures such as injections will affect neuroblast migration and/or the organization of the SVZ.

Electrical resistivity, formation factors, and sound velocity at DSDP Holes 75-530A and 75-530B

From 0 to 277 m at Site 530 are found Holocene to Miocene diatom ooze, nannofossil ooze, marl, clay, and debrisflow deposits; from 277 to 467 m are Miocene to Oligocene mud; from 467 to 1103 m are Eocene to late Albian Cenomanian interbedded mudstone, marlstone, chalk, clastic limestone, sandstone, and black shale in the lower portion; from 1103 to 1121 m are basalts. In the interval from 0 to 467 m, in Holocene to Oligocene pelagic oozes, marl, clay, debris flows, and mud, velocities are 1.5 to 1.8 km/s; below 200 m velocities increase irregularly with increasing depth. From 0 to 100 m, in Holocene to Pleistocene diatom and nannofossil oozes (excluding debris flows), velocities are approximately equivalent to that of the interstitial seawater, and thus acoustic reflections in the upper 100 m are primarily caused by variations in density and porosity. Below 100 or 200 m, acoustic reflections are caused by variations in both velocity and density. From 100 to 467 m, in Miocene-Oligocene nannofossil ooze, clay, marl, debris flows, and mud, acoustic anisotropy irregularly increases to 10%, with 2 to 5% being typical. From 467 to 1103 m in Paleocene to late Albian Cenomanian interbedded mudstone, marlstone, chalk, clastic limestone, and black shale in the lower portion of the hole, velocities range from 1.6 to 5.48 km/s, and acoustic anisotropies are as great as 47% (1.0 km/s) faster horizontally. Mudstone and uncemented sandstone have anisotropies which irregularly increase with increasing depth from 5 to 10% (0.2 km/s). Calcareous mudstones have the greatest anisotropies, typically 35% (0.6 km/s). Below 1103 m, basalt velocities ranged from 4.68 to 4.98 km/s. A typical value is about 4.8 km/s. In situ velocities are calculated from velocity data obtained in the laboratory. These are corrected for in situ temperature, hydrostatic pressure, and porosity rebound (expansion when the overburden pressure is released). These corrections do not include rigidity variations caused by overburden pressures. These corrections affect semiconsolidated sedimentary rocks the most (up to 0.25 km/s faster). These laboratory velocities appear to be greater than the velocities from the sonic log. Reflection coefficients derived from the laboratory data, in general, agree with the major features on the seismic profiles. These indicate more potential reflectors than indicated from the reflection coefficients derived using the Gearhart-Owen Sonic Log from 625 to 940 m, because the Sonic Log data average thin beds. Porosity-density data versus depth for mud, mudstone, and pelagic oozes agree with data for similar sediments as summarized in Hamilton (1976). At depths of about 400 m and about 850 m are zones of relatively higher porosity mudstones, which may suggest anomalously high pore pressure; however, they are more probably caused by variations in grain-size distribution and lithology. Electrical resistivity (horizontal) from 625 to 950 m ranged from about 1.0 to 4.0 ohm-m, in Maestrichtian to Santonian- Coniacian mudstone, marlstone, chalk, clastic limestone, and sandstone. An interstitial-water resistivity curve did not indicate any unexpected lithology or unusual fluid or gas in the pores of the rock. These logs were above the black shale beds. From 0 to 100 m at Sites 530 and 532, the vane shear strength on undisturbed samples of Holocene-Pleistocene diatom and nannofossil ooze uniformly increases from about 80 g/cm**2 to about 800 g/cm**2. From 100 to 300 m, vane shear strength of Pleistocene-Miocene nannofossil ooze, clay, and marl are irregular versus depth with a range of 500 to 2300 g/cm**2; and at Site 532 the vane shear strength appears to decrease irregularly and slightly with increasing depth (gassy zone). Vane shear strength values of gassy samples may not be valid, for the samples may be disturbed as gas evolves, and the sediments may not be gassy at in situ depths.

Dissociation between bone resorption and bone formation in osteopenic transgenic mice

Bone mass is maintained constant in vertebrates through bone remodeling (BR). BR is characterized by osteoclastic resorption of preexisting bone followed by de novo bone formation by osteoblasts. This sequence of events and the fact that bone mass remains constant in physiological situation lead to the assumption that resorption and formation are regulated by each other during BR. Recent evidence shows that cells of the osteoblastic lineage are involved in osteoclast differentiation. However, the existence of a functional link between the two activities, formation and resorption, has never been shown in vivo. To define the role of bone formation in the control of bone resorption, we generated an inducible osteoblast ablation mouse model. These mice developed a reversible osteopenia. Functional analyses showed that in the absence of bone formation, bone resorption continued to occur normally, leading to an osteoporosis of controllable severity, whose appearance could be prevented by an antiresorptive agent. This study establishes that bone formation and/or bone mass do not control the extent of bone resorption in vivo.

Extraction of Cholesterol with Methyl-β-Cyclodextrin Perturbs Formation of Clathrin-coated Endocytic Vesicles

The importance of cholesterol for endocytosis has been investigated in HEp-2 and other cell lines by using methyl-β-cyclodextrin (MβCD) to selectively extract cholesterol from the plasma membrane. MβCD treatment strongly inhibited endocytosis of transferrin and EGF, whereas endocytosis of ricin was less affected. The inhibition of transferrin endocytosis was completely reversible. On removal of MβCD it was restored by continued incubation of the cells even in serum-free medium. The recovery in serum-free medium was inhibited by addition of lovastatin, which prevents cholesterol synthesis, but endocytosis recovered when a water-soluble form of cholesterol was added together with lovastatin. Electron microscopical studies of MβCD-treated HEp-2 cells revealed that typical invaginated caveolae were no longer present. Moreover, the invagination of clathrin-coated pits was strongly inhibited, resulting in accumulation of shallow coated pits. Quantitative immunogold labeling showed that transferrin receptors were concentrated in coated pits to the same degree (approximately sevenfold) after MβCD treatment as in control cells. Our results therefore indicate that although clathrin-independent (and caveolae-independent) endocytosis still operates after removal of cholesterol, cholesterol is essential for the formation of clathrin-coated endocytic vesicles.

Rescue of stalled replication forks by RecG: Simultaneous translocation on the leading and lagging strand templates supports an active DNA unwinding model of fork reversal and Holliday junction formation

Modification of damaged replication forks is emerging as a crucial factor for efficient chromosomal duplication and the avoidance of genetic instability. The RecG helicase of Escherichia coli, which is involved in recombination and DNA repair, has been postulated to act on stalled replication forks to promote replication restart via the formation of a four-stranded (Holliday) junction. Here we show that RecG can actively unwind the leading and lagging strand arms of model replication fork structures in vitro. Unwinding is achieved in each case by simultaneous interaction with and translocation along both the leading and lagging strand templates at a fork. Disruption of either of these interactions dramatically inhibits unwinding of the opposing duplex arm. Thus, RecG translocates simultaneously along two DNA strands, one with 5′-3′ and the other with 3′-5′ polarity. The unwinding of both nascent strands at a damaged fork, and their subsequent annealing to form a Holliday junction, may explain the ability of RecG to promote replication restart. Moreover, the preferential binding of partial forks lacking a leading strand suggests that RecG may have the ability to target stalled replication intermediates in vivo in which lagging strand synthesis has continued beyond the leading strand.