RESUMO
Using whole-brain structural measures coupled to analysis of salivary brain-derived neurotrophic factor (BDNF), we demonstrate sensory motor training-induced plasticity, including cerebellar gray matter volume increment and increased BDNF level. The increase of cerebellar volume was positively correlated with the increase of BDNF level.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/metabolismo , Cerebelo/anatomia & histologia , Prática Psicológica , Desempenho Psicomotor/fisiologia , Adulto , Western Blotting , Cerebelo/fisiologia , Imagem de Tensor de Difusão , Eletroforese em Gel de Poliacrilamida , Feminino , Substância Cinzenta/anatomia & histologia , Substância Cinzenta/fisiologia , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Pessoa de Meia-Idade , Plasticidade Neuronal/fisiologia , Tamanho do Órgão , Saliva/metabolismoRESUMO
The ability of cells to respond to changes in their environment is mediated by transcription factors that remodel chromatin and reprogram expression of specific subsets of genes. In Saccharomyces cerevisiae, changes in carbon source lead to gene induction by Adr1 and Cat8 that are known to require the upstream function of the Snf1 protein kinase, the central regulator of carbon metabolism, to exert their activating effect. How Snf1 facilitates transcription activation by Adr1 and Cat8 is not known. Here we show that under derepressing conditions, deletion of SNF1 abolishes the increase of histone H3 acetylation at the promoter of the glucose-repressed ADY2 gene, and as a consequence profoundly affects the chromatin structural alterations accompanying transcriptional activation. Adr1 and Cat8 are not required to regulate the acetylation switch and show only a partial influence on chromatin remodelling at this promoter, though their double deletion completely abolishes mRNA accumulation. Finally, we show that under derepressing conditions the recruitment of the histone acetyltransferase Gcn5 is abolished by SNF1 deletion, possibly explaining the lack of increased histone H3 acetylation and nucleosome remodelling. The results highlight a mechanism by which signalling to chromatin provides an essential permissive signal that is required for activation by glucose-responsive transcription factors.
Assuntos
Montagem e Desmontagem da Cromatina/genética , Proteínas de Membrana Transportadoras , Proteínas Serina-Treonina Quinases , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Ativação Transcricional , Acetilação/efeitos dos fármacos , Carbono/metabolismo , Montagem e Desmontagem da Cromatina/efeitos dos fármacos , Proteínas de Ligação a DNA/metabolismo , Glucose/metabolismo , Glucose/farmacologia , Histona Acetiltransferases/genética , Histona Acetiltransferases/metabolismo , Histonas/metabolismo , Proteínas de Membrana Transportadoras/genética , Proteínas de Membrana Transportadoras/metabolismo , Regiões Promotoras Genéticas , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Transdução de Sinais , Transativadores/metabolismo , Fatores de Transcrição/metabolismo , Ativação Transcricional/efeitos dos fármacos , Ativação Transcricional/genéticaRESUMO
Many environmental and lifestyle related factors may influence the physiology of the brain and body by acting on fundamental molecular pathways, such as the hypothalamus-pituitary-adrenal axis (HPA) and the immune system. For example, stressful conditions created by adverse early-life events, unhealthy habits and low socio-economic status may favor the onset of diseases linked to neuroendocrine dysregulation, inflammation and neuroinflammation. Beside pharmacological treatments used in clinical settings, much attention has been given to complementary treatments such as mind-body techniques involving meditation that rely on the activation of inner resources to regain health. At the molecular level, the effects of both stress and meditation are elicited epigenetically through a set of mechanisms that regulate gene expression as well as the circulating neuroendocrine and immune effectors. Epigenetic mechanisms constantly reshape genome activities in response to external stimuli, representing a molecular interface between organism and environment. In the present work, we aimed to review the current knowledge on the correlation between epigenetics, gene expression, stress and its possible antidote, meditation. After introducing the relationship between brain, physiology, and epigenetics, we will proceed to describe three basic epigenetic mechanisms: chromatin covalent modifications, DNA methylation and non-coding RNAs. Subsequently, we will give an overview of the physiological and molecular aspects related to stress. Finally, we will address the epigenetic effects of meditation on gene expression. The results of the studies reported in this review demonstrate that mindful practices modulate the epigenetic landscape, leading to increased resilience. Therefore, these practices can be considered valuable tools that complement pharmacological treatments when coping with pathologies related to stress.
Assuntos
Meditação , Humanos , Encéfalo , Epigênese Genética , Sistema Hipotálamo-Hipofisário , InflamaçãoRESUMO
Mind-body practices and meditation have been increasingly studied in recent years due to their beneficial effects on cognition, and physical and psychological health. Growing evidence suggests that these practices could be utilized as interventions to impact age-related biological processes, such as cognitive decline, inflammation, and homeostatic dysregulation. Indeed, it has been reported that mindful meditation may induce neuroplasticity in brain regions involved in control of attention, emotional regulation, and self-awareness. In the current research we studied the effects of a recently developed movement meditation, named the Quadrato Motor Training (QMT), on the proinflammatory cytokine Interleukin-1beta (IL-1ß), utilizing a pre-post design. In addition to its role in the immune system, IL-1ß is also an important mediator of neuroimmune responses related to sickness behavior, and plays a role in complex cognitive processes, such as synaptic plasticity, neurogenesis, and neuromodulation. Thirty healthy participants were divided in two groups, one performing QMT for 2 months, and one passive control group. Salivary IL-1ß expression was examined by ELISA to measure protein levels and by qRT-PCR to quantify mRNA. In addition, the methylation profile of the IL-1ß promoter was examined. All participants further conducted the Alternate Uses Task (AUT) and Hidden Figure Test (HFT), to measure their creativity and spatial cognition. The results showed that, following QMT practice, IL-1ß protein level decreased and creativity increased, compared to the control group. These data demonstrate that QMT may help reduce inflammatory states and promote cognitive improvement, highlighting the importance of non-pharmacological approaches to health and well-being.
Assuntos
Cognição , Criatividade , Condicionamento Físico Humano , Humanos , Encéfalo , Cognição/fisiologia , Interleucina-1beta/metabolismo , Condicionamento Físico Humano/métodosRESUMO
The control of non-coding repeated DNA by DNA methylation plays an important role in genomic stability, contributing to health and healthy aging. Mind-body practices can elicit psychophysical wellbeing via epigenetic mechanisms, including DNA methylation. However, in this context the effects of movement meditations have rarely been examined. Consequently, the current study investigates the effects of a specifically structured movement meditation, called the Quadrato Motor Training (QMT) on psychophysical wellbeing and on the methylation level of repeated sequences. An 8-week daily QMT program was administered to healthy women aged 40-60 years and compared with a passive control group matched for gender and age. Psychological well-being was assessed within both groups by using self-reporting scales, including the Meaning in Life Questionnaire [MLQ] and Psychological Wellbeing Scale [PWB]). DNA methylation profiles of repeated sequences (ribosomal DNA, LINE-1 and Alu) were determined in saliva samples by deep-sequencing. In contrast to controls, the QMT group exhibited increased Search for Meaning, decreased Presence of Meaning and increased Positive Relations, suggesting that QMT may lessen the automatic patterns of thinking. In the QMT group, we also found site-specific significant methylation variations in ribosomal DNA and LINE-1 repeats, consistent with increased genome stability. Finally, the correlations found between changes in methylation and psychometric indices (MLQ and PWB) suggest that the observed epigenetic and psychological changes are interrelated. Collectively, the current results indicate that QMT may improve psychophysical health trajectories by influencing the DNA methylation of specific repetitive sequences.
Assuntos
Metilação de DNA , Movimento , Humanos , Feminino , Projetos Piloto , Epigênese Genética , DNA RibossômicoRESUMO
Insight into the mechanisms by which ambient air particulate matter mediates adverse health effects is needed to provide biological plausibility to epidemiological studies demonstrating an association between PM(10) exposure and increased morbidity and mortality. In vitro studies of the effects of air pollution on human cells help to establish conditions for the analysis of cause-effect relationships. One of the major challenges is to test native atmosphere in its complexity, rather than the various components individually. We have developed an in vitro system in which human monocyte-macrophage U937 cells are directly exposed to filters containing different amounts of PM(10) collected in the city of Rome. Transcriptional profiling obtained after short exposure (1h) of cells to a filter containing 1666µg PM(10) (77.6µg/cm(2)) using a macroarray panel of 1176 genes reveals a significant change in the mRNA level (>2 fold) for 87 genes relative to cells exposed to a control filter. Overall, 9 out of 87 modulated genes were annotated as "lung cancer". qRT-PCR confirmed the induction of relevant genes involved in DNA repair and apoptosis, specifically: ERCC1, TDG, DAD1 and MCL1. In cells exposed for 10min, 1h and 3h to different amounts of PM(10), transcription of TNFα and TRAP1, which code for a key pro-inflammatory cytokine and a mitochondrial protein involved in cell protection from oxidative stress, respectively, was shown to be modulated in a time-dependent, but not a dose-dependent manner. Taken together, these data indicate that it is possible to analyze the effects of untreated particulate matter on human cells by the direct-exposure approach we have developed, possibly providing new clues to traffic-related health hazard.
Assuntos
Poluentes Atmosféricos/toxicidade , Exposição Ambiental , Monócitos/efeitos dos fármacos , Monócitos/metabolismo , Material Particulado/toxicidade , Transcrição Gênica/efeitos dos fármacos , Apoptose/efeitos dos fármacos , Apoptose/genética , Linhagem Celular , Reparo do DNA/efeitos dos fármacos , Reparo do DNA/genética , Perfilação da Expressão Gênica , Proteínas de Choque Térmico HSP90/biossíntese , Humanos , Tamanho da Partícula , Cidade de Roma , Fator de Necrose Tumoral alfa/biossínteseRESUMO
In vivo nucleosomes often occupy well-defined preferred positions on genomic DNA. An important question is to what extent these preferred positions are directly encoded by the DNA sequence itself. We derive here from in vivo positions, accurately mapped by partial micrococcal nuclease digestion, a translational positioning signal that identifies the approximate midpoint of DNA bound by a histone octamer. This midpoint is, on average, highly A/T rich ( approximately 73%) and, in particular, the dinucleotide TpA occurs preferentially at this and other outward-facing minor grooves. We conclude that in this set of sequences the sequence code for DNA bending and nucleosome positioning differs from the other described sets and we suggest that the enrichment of AT-containing dinucleotides at the centre is required for local untwisting. We show that this signature is preferentially associated with nucleosomes flanking promoter regions and suggest that it contributes to the establishment of gene-specific nucleosome arrays.
Assuntos
DNA/química , Nucleossomos/química , Biossíntese de Proteínas , Sequência Rica em At , Nuclease do Micrococo , Análise de Sequência de DNARESUMO
Many studies have consistently demonstrated an epigenetic link between environmental stimuli and physiological as well as cognitive responses. Epigenetic mechanisms represent a way to regulate gene activity in real time without modifying the DNA sequence, thus allowing the genome to adapt its functions to changing environmental contexts. Factors such as lifestyle, behavior, and the practice of sitting and moving mindful activities have been shown to be important means of environmental enrichment. Such practices, which include mindfulness meditation, Vipassana, Yoga, Tai Chi, and Quadrato Motor Training, have been reported to positively impact well-being. In fact, they can be considered emotional and attentional regulatory activities, which, by inducing a state of greater inner silence, allow the development of increased self-awareness. Inner silence can therefore be considered a powerful tool to counteract the negative effects of overabundant environmental noise, thanks to its power to relieve stress-related symptoms. Since all these positive outcomes rely on physiological and biochemical activities, the molecular and epigenetic mechanisms influenced by different mindful practices have recently started to be investigated. Here, we review some of the findings that could allow us to uncover the mechanisms by which specific practices influence well-being.
RESUMO
Previous studies demonstrated exercise-induced modulation of neurotrophins, such as Nerve Growth Factor (NGF) and Brain-Derived Neurotrophic Factor (BDNF). Yet, no study that we are aware of has examined their change as a function of different training paradigms. In addition, the understanding of the possible training-induced relationship between NGF and BDNF change is still lacking. Consequently, in the current study we examined the effect of a Walking Training (WT) and of Quadrato Motor Training (QMT) on NGF and BDNF precursors (proNGF and proBDNF). QMT is a specifically structured sensorimotor training that involves sequences of movements based on verbal commands, that was previously reported to improve spatial cognition, reflectivity, creativity as well as emotion regulation and general self-efficacy. In addition, QMT was reported to induce electrophysiological and morphological changes, suggesting stimulation of neuroplasticity processes. In two previous independent studies we reported QMT-induced changes in the salivary proNGF and proBDNF levels. Our present results demonstrate that following 12 weeks of daily QMT practice, proNGF level increases while proBDNF showed no significant change. More importantly, while no correlation between the two neurotrophins prior to training was detectable, there was a significant correlation between change in proNGF and proBDNF levels. Taken together the current results suggest that the two neurotrophins undergo a complex modulation, likely related to the different pathways by which they are produced and regulated. Since variations of these neurotrophins have been previously linked to depression, stress and anxiety, the current study may have practical implications and aid in understanding the possible physiological mechanisms that mediate improved well-being, and the dynamic change of neurotrophins as a result of training.
RESUMO
Poly(ADP-ribosyl)ation (PARylation) is a posttranslational protein modification catalyzed by members of the poly(ADP-ribose) polymerase (PARP) enzyme family. PARylation regulates a wide variety of biological processes in most eukaryotic cells including energy metabolism and cell death, maintenance of genomic stability, chromatin structure and transcription. Inside the nucleus, cross-talk between PARylation and other epigenetic modifications, such as DNA and histone methylation, was already described. In the present work, using PJ34 or ABT888 to inhibit PARP activity or over-expressing poly(ADP-ribose) glycohydrolase (PARG), we show decrease of global histone H3 and H4 acetylation. This effect is accompanied by a reduction of the steady state mRNA level of p300, Pcaf, and Tnfα, but not of Dnmt1. Chromatin immunoprecipitation (ChIP) analyses, performed at the level of the Transcription Start Site (TSS) of these four genes, reveal that changes in histone acetylation are specific for each promoter. Finally, we demonstrate an increase of global deacetylase activity in nuclear extracts from cells treated with PJ34, whereas global acetyltransferase activity is not affected, suggesting a role for PARP in the inhibition of histone deacetylases. Taken together, these results show an important link between PARylation and histone acetylation regulated transcription.
Assuntos
Histonas/metabolismo , Poli Adenosina Difosfato Ribose/metabolismo , Poli(ADP-Ribose) Polimerases/metabolismo , Transcrição Gênica , Acetilação , Animais , Benzimidazóis/farmacologia , DNA (Citosina-5-)-Metiltransferase 1 , DNA (Citosina-5-)-Metiltransferases/biossíntese , Proteína p300 Associada a E1A/biossíntese , Instabilidade Genômica , Camundongos , Células NIH 3T3 , Fenantrenos/farmacologia , Fator de Necrose Tumoral alfa/biossíntese , Fatores de Transcrição de p300-CBP/biossínteseRESUMO
Mind-body practices (MBP) are known to induce electrophysiological and morphological changes, whereas reports related to changes of neurotrophins are surprisingly scarce. Consequently, in the current paper, we focused on the Quadrato motor training (QMT), a newly developed whole-body movement-based MBP, which has been reported to enhance creativity. Here we report the effects of 4 weeks of daily QMT on creativity and proNGF level in two interrelated studies. In Study A, we examined the effects of QMT compared with a walking training (WT) in healthy adults, utilizing the alternate uses task. In contrast with the WT, QMT resulted in increased creativity. In addition, the change in creativity negatively correlated with the change in proNGF levels. In Study B, we examined QMT effects on creativity and additional metacognitive functions in children, using a nonintervention group as control. Similar to Study A, following QMT, we found a negative correlation of proNGF with creativity, as well as working memory updating and planning ability. Together, the current results point to the relationship between increased creativity and decreased proNGF following MBP. Thus, the current research emphasizes the importance of widening the scope of examination of "MBP in motion" in relation to metacognition and well-being.
Assuntos
Cognição/fisiologia , Criatividade , Memória de Curto Prazo/fisiologia , Psicofisiologia , Adulto , Feminino , HumanosRESUMO
The contribution of histone-DNA interactions to nucleosome positioning in vivo is currently a matter of debate. We argue here that certain nucleosome positions, often in promoter regions, in yeast may be, at least in part, specified by the DNA sequence. In contrast other positions may be poorly specified. Positioning thus has both statistical and DNA-determined components. We further argue that the relative affinity of the octamer for different DNA sequences can vary and therefore the interaction of histones with the DNA is a 'tunable' property.
Assuntos
Montagem e Desmontagem da Cromatina/genética , Nucleossomos/genética , Nucleossomos/metabolismo , Animais , Sequência de Bases , Histonas/metabolismo , HumanosRESUMO
The positioning of nucleosomes on the DNA of eukaryotic genomes is a major determinant of gene expression. In particular nucleosomes in close proximity to regulatory regions are often more precisely positioned in vivo than nucleosomes located elsewhere. In this article we compare data obtained from the most recent studies by a variety of techniques. We argue that the disparate conclusions in the literature could be a consequence of procedural differences sampling alternative arrays of nucleosomes on the same DNA sequence. Importantly, the ostensibly least invasive techniques identify differences between nucleosomes in the vicinity of transcription start sites in budding yeast and those positioned distally within the transcribed region.
Assuntos
Sequência de Bases , Modelos Genéticos , Nucleossomos/fisiologia , Animais , Simulação por Computador , Nucleossomos/genética , Saccharomycetales/fisiologiaRESUMO
Histone acetylation regulates gene expression. Whether this is caused by a general increase in nucleosome fluidity due to charge neutralization or by a more specific code is still matter of debate. By using a set of glucose-repressed Adr1-dependent genes of Saccharomyces cerevisiae, whose transcription was previously shown to require both Gcn5 and Esa1, we asked how changes of histone acetylation patterns at the promoter nucleosomes regulate chromatin remodelling and activation. When the signal of glucose reduction reaches the cells, H4 acetylation is kept constant while an increase of H3 acetylation occurs, in an Adr1- and Gcn5-dependent manner. In cells lacking Gcn5 activity, the H3 acetylation increase does not occur and an unexpected increase of histone H4 acetylation is observed. Nevertheless, chromatin remodelling and transcription activation are impaired, suggesting that acetylation of H3 and H4 histones plays different roles.
Assuntos
Cromatina/metabolismo , Proteínas de Ligação a DNA/metabolismo , Proteínas Fúngicas/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/genética , Fatores de Transcrição/metabolismo , Transcrição Gênica , Acetilação , Proteínas Fúngicas/química , Histonas/metabolismo , Transativadores/genéticaRESUMO
Genetic information is packaged in the highly dynamic nucleoprotein structure called chromatin. Many biological processes are regulated via post-translational modifications of key proteins. Acetylation of lysine residues at the N-terminal histone tails is one of the most studied covalent modifications influencing gene regulation in eukaryotic cells. This review focuses on the role of enzymes involved in controlling both histone and non-histone proteins acetylation levels in the cell, with particular emphasis on their effects on cancer.
Assuntos
Regulação da Expressão Gênica , Histonas/metabolismo , Processamento de Proteína Pós-Traducional , Acetilação , Animais , Cromatina/metabolismo , Epigênese Genética , Histona Acetiltransferases/genética , Histona Acetiltransferases/metabolismo , Inibidores de Histona Desacetilases , Histona Desacetilases/metabolismo , Humanos , Modelos Biológicos , Neoplasias/genética , Neoplasias/metabolismoRESUMO
Nucleosome remodelling complexes play a key role in gene activation in response to environmental changes by driving promoter chromatin to reach an accessible configuration. They also mediate genome-wide chromatin organization, although their role in processes other than activation-related chromatin remodelling are poorly understood. The Saccharomyces cerevisiae ADH2 gene represents an excellent model for understanding the role of chromatin structure and remodelling in gene regulation. Following glucose depletion, highly positioned promoter nucleosomes are destabilized leading to strictly regulated kinetics of transcriptional activation. Nevertheless, no chromatin remodelling activities responsible for establishing or remodelling ADH2 chromatin structure have been identified to date. Here we show that the absence of the Isw1 and Chd1 ATP-dependent chromatin remodelling activities delays the maximal expression of ADH2 without impairing the chromatin remodelling that occurs upon activation. Instead, a destabilized chromatin structure on the ADH2 coding and termination region is observed in the absence of Isw1 or Chd1 in repressing conditions. The specific Isw1 complex involved in this nucleosome repositioning is Isw1b because the deletion of Ioc2 and Ioc4, but not of Ioc3, causes the same phenotype as the deletion of Isw1. Moreover, the lack of Chd1 combined with the absence of Isw1 and Isw2 impairs nucleosome spacing along the ADH2 gene, and genome-wide in S. cerevisiae. Thus, the ISWI and Chd1 remodelling factors are not only involved in transcription-related chromatin remodelling, but also are required to maintain a specific chromatin configuration across the yeast genome.
Assuntos
Adenosina Trifosfatases/metabolismo , Álcool Desidrogenase/genética , Montagem e Desmontagem da Cromatina , Cromatina/química , Proteínas de Ligação a DNA/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Fatores de Transcrição/metabolismo , Adenosina Trifosfatases/genética , Álcool Desidrogenase/metabolismo , Proteínas de Ligação a DNA/genética , Deleção de Genes , Regulação Fúngica da Expressão Gênica , Genoma Fúngico , Cinética , Mutação , Nucleossomos/metabolismo , Regiões Promotoras Genéticas , Saccharomyces cerevisiae/fisiologia , Fatores de Transcrição/genética , Ativação TranscricionalRESUMO
Histone proteins play structural and functional roles in all nuclear processes. They undergo different types of covalent modifications, defined in their ensemble as epigenetic because changes in DNA sequences are not involved. Histone acetylation emerges as a central switch that allows interconversion between permissive and repressive chromatin domains in terms of transcriptional competence. The mechanisms underlying the histone acetylation-dependent control of gene expression include a direct effect on the stability of nucleosomal arrays and the creation of docking sites for the binding of regulatory proteins. Histone acetyltransferases and deacetylases are, respectively, the enzymes devoted to the addition and removal of acetyl groups from lysine residues on the histone N-terminal tails. The enzymes exert fundamental roles in developmental processes and their deregulation has been linked to the progression of diverse human disorders, including cancer.
Assuntos
Regulação da Expressão Gênica , Histonas/química , Acetilação , Acetiltransferases/metabolismo , Animais , DNA/metabolismo , Proteínas Fúngicas/química , Genoma , Histona Acetiltransferases , Humanos , Camundongos , Modelos Biológicos , Nucleossomos/metabolismo , Estrutura Terciária de Proteína , Transcrição GênicaRESUMO
The involvement of chromatin structure and organization in transcriptional regulatory pathways has become evident. One unsolved question concerns the molecular mechanisms of chromatin remodeling during in vivo promoter activation. By using a high resolution in vivo analysis we show that when yeast cells are exposed to a regulatory signal the positions of specific nucleosomes change. The system analyzed consists of the basic elements of the Saccharomyces cerevisiae ADH2 promoter, two nucleosomes of which are shown to change the distribution of their positions by few nucleotides in the direction of transcription when the glucose content of the medium is lowered. Such repositioning does not occur in the absence of the ADH2 transcriptional activator Adr1 or in the presence of its DNA-binding domain alone. A construct consisting of the DNA-binding domain plus a 43-amino acid peptide containing the Adr1 activation domain is sufficient to induce the same effect of the full-length protein. Nucleosome repositioning occurs even when the catalytic activity of the RNA polymerase II is impaired, suggesting that the Adr1 activation domain mediates the recruitment of some factor to correctly preset the relevant sequences for the subsequent transcription steps.
Assuntos
Nucleossomos/química , Nucleossomos/fisiologia , Regiões Promotoras Genéticas , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Transcrição Gênica , Northern Blotting , Catálise , Cromatina/metabolismo , Proteínas de Ligação a DNA/química , Modelos Genéticos , Nucleossomos/metabolismo , Peptídeos/química , Plasmídeos/metabolismo , Estrutura Terciária de Proteína , RNA/metabolismo , RNA Mensageiro/metabolismo , Temperatura , Fatores de Transcrição/químicaRESUMO
Nucleosomes have been considered until recently to be stable and uniquely localized particles. We focus here on two properties of nucleosomes that are emerging as central attributes of their functions: mobility and multiplicity of localization. The biological relevance of these phenomena is based on the fact that chromatin functions depend on the relative stability of nucleosomes, on their covalent or conformational modifications, their dynamics, their localization, and the density of their distribution. In order to understand these complex behaviors both the structure of the nucleosome core particles and the informational rules governing their interaction with defined DNA sequences are here taken into consideration. The fact that nucleosomes solve the problem of how to locate a specific interaction site on a potentially infinite combination of sequences, with interactions recurring to a controlled level of informational ambiguity and stochasticity, is discussed. Nucleosomes have been shown to slide along DNA. This novel facet of their behavior and its implications in chromatin remodeling are reviewed.
Assuntos
Nucleossomos/química , Nucleossomos/metabolismo , DNA/metabolismo , Movimento , Nucleossomos/ultraestrutura , Regiões Promotoras Genéticas , Transcrição GênicaRESUMO
The chromatin structure of several Saccharomyces cerevisiae ADR1-dependent genes was comparatively analyzed in vivo in order to evaluate the role of promoter architecture in transcriptional control. In repressing conditions (high glucose) a nucleosome particle always obstructs the TATA box, immediately adjacent to an upstream-located nucleosome-free region containing a cluster of Adr1 binding sites. Upon derepression the TATA box-containing nucleosome is destabilized according to a mechanism shared by all of the genes studied. The transcription factor Adr1 is always required for the observed chromatin remodeling. mRNA accumulation of all of the genes analyzed is strongly delayed in the absence of the acetyltransferase Gcn5 and is decreased in the presence of a temperature-sensitive Esa1 mutant. The results suggest that a defined promoter chromatin structure, controlled by DNA conformational features, is relevant for the activation of coregulated genes.