Total and inorganic arsenic in dietary supplement supplies in northern Mexico.

The aim of this study was to evaluate the presence of total and inorganic arsenic in dietary supplements composed of herbal plants and seaweed, and to determine the potential toxicological risk. Total arsenic was determined by dry ashing and hydride generation atomic absorption spectrometry, and inorganic arsenic was determined by acid digestion, solvent extraction, and hydride generation atomic absorption spectrometry. Total and inorganic arsenic in the supplements ranged from 0.07 to 8.31 mg kg(-1) dry weight and from 0.14 to 0.28 mg kg(-1) dry weight, respectively. Daily intake of total arsenic ranged from 0.05 to 12.46 µg day(-1). Inorganic arsenic intake ranged from 0.21 to 0.83 µg day(-1), values that are below the Benchmark Dose Lower Confidence Limit recommended by the Word Health Organization. Therefore, there appears to be a low risk of adverse effects resulting from excess inorganic arsenic intake from these supplements. This is the first study conducted in Mexico that investigates total and inorganic arsenic in dietary supplements. Although the results do not suggest toxicological risk, it is nonetheless important considering the toxicity of inorganic arsenic and the increasing number consumer preferences for dietary supplements. Moreover, it is important to improve and ensure the safety of dietary supplements containing inorganic arsenic.

A key role for Chd1 in histone H3 dynamics at the 3' ends of long genes in yeast.

Chd proteins are ATP-dependent chromatin remodeling enzymes implicated in biological functions from transcriptional elongation to control of pluripotency. Previous studies of the Chd1 subclass of these proteins have implicated them in diverse roles in gene expression including functions during initiation, elongation, and termination. Furthermore, some evidence has suggested a role for Chd1 in replication-independent histone exchange or assembly. Here, we examine roles of Chd1 in replication-independent dynamics of histone H3 in both Drosophila and yeast. We find evidence of a role for Chd1 in H3 dynamics in both organisms. Using genome-wide ChIP-on-chip analysis, we find that Chd1 influences histone turnover at the 5' and 3' ends of genes, accelerating H3 replacement at the 5' ends of genes while protecting the 3' ends of genes from excessive H3 turnover. Although consistent with a direct role for Chd1 in exchange, these results may indicate that Chd1 stabilizes nucleosomes perturbed by transcription. Curiously, we observe a strong effect of gene length on Chd1's effects on H3 turnover. Finally, we show that Chd1 also affects histone modification patterns over genes, likely as a consequence of its effects on histone replacement. Taken together, our results emphasize a role for Chd1 in histone replacement in both budding yeast and Drosophila melanogaster, and surprisingly they show that the major effects of Chd1 on turnover occur at the 3' ends of genes.

Content of selenium, total and inorganic arsenic and bioaccessibility of arsenic in children diets of Mexico.

BACKGROUND: The aim of this study was to evaluate the intake of selenium, total and inorganic arsenic and the bioaccessibility of arsenic in diets of Mexican schoolchildren using an in vitro method. RESULTS: Total and inorganic arsenic concentrations in the diets ranged from 0.05 to 1.15 mg kg(-1) dry weight (DW) and from 0.023 to 0.088 mg kg(-1) DW respectively, while selenium levels were between 0.08 and 0.20 mg kg(-1) DW. Daily intake of total and inorganic arsenic ranged from 0.15 to 10.49 µg day(-1) kg(-1) body weight (BW) and from 0.06 to 1.11 µg day(-1) kg(-1) BW respectively, while that of selenium varied from 0.29 to 2.63 µg day(-1) kg(-1) BW. Bioaccessibility of total and inorganic arsenic ranged from 4 to 97% (mean 44 ± 21.5%) and from 33 to 97% (mean 71 ± 22.5%) respectively. CONCLUSION: Inorganic arsenic levels in the diets were low. Therefore there appears to be a low risk of adverse effects resulting from excess inorganic arsenic intake from these diets.

Dissolved and particulate metals in water from Sonora Coast: a pristine zone of Gulf of California: metals in water from Sonora Coast.

The purpose of this study was to investigate the distribution of metals (Cd, Pb, Hg, Cu, Fe, Mn, and Zn) in dissolved and particulate fractions in seawater from Bacochibampo Bay, Northern part of Mexico. Water samples were collected from November 2004 to October 2005. Metal analysis was done by graphite furnace atomic absorption spectroscopy. Results indicated highest concentrations of dissolved Cd and Zn in the sites localized at the mouth and center of the bay. During summer and spring, the highest levels of Cd, Mn, and Fe were detected, Zn in fall, and Pb and Cu in winter and spring. Mercury was the only metal that was not found in this fraction. In particulate fraction, Fe, Hg, and Mn were the most abundant elements in all the sampling sites, followed by Zn, Cu, Pb, and Cd. The highest levels of the majority of the metals were observed in the coastline, suggesting a continental and/or urban source for these chemicals. The highest level of Cd was detected during the summer and the rest of the metals in the fall. Statistically significant correlations were observed between dissolved and particulate forms of Pb:Mn, Cu:Fe, and Cu:Mn. The mean partition coefficient values were as follows: Fe>Mn>Cu>Pb>Cd>Zn. All dissolved metal concentrations found, except Pb, were lower than EPA-recommended water quality values. The levels of dissolved metals in this study reveal low bioavailability and toxic potential. However, further toxicological and sediment chemistry studies in this area are needed for a full risk assessment.

Transcription independent insulation at TFIIIC-dependent insulators.

Chromatin insulators separate active from repressed chromatin domains. In yeast the RNA pol III transcription machinery bound to tRNA genes function with histone acetylases and chromatin remodelers to restrict the spread of heterochromatin. Our results collectively demonstrate that binding of TFIIIC is necessary for insulation but binding of TFIIIB along with TFIIIC likely improves the probability of complex formation at an insulator. Insulation by this transcription factor occurs in the absence of RNA polymerase III or polymerase II but requires specific histone acetylases and chromatin remodelers. This analysis identifies a minimal set of factors required for insulation.

Long-range communication between the silencers of HMR.

Gene regulation involves long-range communication between silencers, enhancers, and promoters. In Saccharomyces cerevisiae, silencers flank transcriptionally repressed genes to mediate regional silencing. Silencers recruit the Sir proteins, which then spread along chromatin to encompass the entire silenced domain. In this report we have employed a boundary trap assay, an enhancer activity assay, chromatin immunoprecipitations, and chromosome conformation capture analyses to demonstrate that the two HMR silencer elements are in close proximity and functionally communicate with one another in vivo. We further show that silencing is necessary for these long-range interactions, and we present models for Sir-mediated silencing based upon these results.

Chromatin insulators.

Active and silenced chromatin domains are often in close juxtaposition to one another, and enhancer and silencer elements operate over large distances to regulate the genes in these domains. The lack of promiscuity in the function of these elements suggests that active mechanisms exist to restrict their activity. Insulators are DNA elements that restrict the effects of long-range regulatory elements. Studies on different insulators from different organisms have identified common themes in their mode of action. Numerous insulators map to promoters of genes or have binding sites for transcription factors and like active chromatin hubs and silenced loci, insulators also cluster in the nucleus. These results bring into focus potential conserved mechanisms by which these elements might function in the nucleus.

Gcn5p contributes to the bidirectional character of the UGA3-GLT1 yeast promoter.

Analysis of the UGA3-GLT1 bidirectional promoter has indicated that its transcriptional activation is determined by the combined action of Gcn4p and Gln3p, and that its bidirectional character is influenced by chromatin organization, through the action of an Abf1p binding site and a polydAdTtract. Results presented in this paper show that lack of Gcn5p impairs histone acetylation and nucleosomal organization of the UGA3-GLT1 promoter, resulting in an asymmetrical transcriptional activation response of UGA3 and GLT1. The phenotype displayed by a double mutant impaired in GCN5 and in the Abf1p binding site indicates that the combined action of these two elements determines the bidirectional capacity of the UGA3-GLT1 intergenic region.

The UGA3-GLT1 intergenic region constitutes a promoter whose bidirectional nature is determined by chromatin organization in Saccharomyces cerevisiae.

Transcription of an important number of divergent genes of Saccharomyces cerevisiae is controlled by intergenic regions, which constitute factual bidirectional promoters. However, few of such promoters have been characterized in detail. The analysis of the UGA3-GLT1 intergenic region has provided an interesting model to study the joint action of two global transcriptional activators that had been considered to act independently. Our results show that Gln3p and Gcn4p exert their effect upon cis-acting elements, which are shared in a bidirectional promoter. Accordingly, when yeast is grown on a low-quality nitrogen source, or under amino acid deprivation, the expression of both UGA3 and GLT1 is induced through the action of both these global transcriptional modulators that bind to a region of the bidirectional promoter. In addition, we demonstrate that chromatin organization plays a major role in the bidirectional properties of the UGA3-GLT1 promoter, through the action of an upstream Abf1p-binding consensus sequence and a polydAdT(tract). Mutations in these cis-elements differentially affect transcription of UGA3 and GLT1, and thus alter the overall relative expression. This is the first example of an intergenic region constituting a promoter whose bidirectional character is determined by chromatin organization.

Analyses of SUM1-1-mediated long-range repression.

In Saccharomyces cerevisiae, local repression is promoter specific and localized to a small region on the DNA, while silencing is promoter nonspecific, encompasses large domains of chromatin, and is stably inherited for multiple generations. Sum1p is a local repressor protein that mediates repression of meiosis-specific genes in mitotic cells while the Sir proteins are long-range repressors that stably silence genes at HML, HMR, and telomeres. The SUM1-1 mutation is a dominant neomorphic mutation that enables the mutant protein to be recruited to the HMR locus and repress genes, even in the absence of the Sir proteins. In this study we show that the mutation in Sum1-1p enabled it to spread, and the native HMR barrier blocked it from spreading. Thus, like the Sir proteins, Sum1-1p was a long-range repressor, but unlike the Sir proteins, Sum1-1p-mediated repression was more promoter specific, repressing certain genes better than others. Furthermore, repression mediated by Sum1-1p was not stably maintained or inherited and we therefore propose that Sum1-1p-mediated long-range repression is related but distinct from silencing.

Swi/SNF-GCN5-dependent chromatin remodelling determines induced expression of GDH3, one of the paralogous genes responsible for ammonium assimilation and glutamate biosynthesis in Saccharomyces cerevisiae.

It is accepted that Saccharomyces cerevisiae genome arose from complete duplication of eight ancestral chromosomes; functionally normal ploidy was recovered because of the massive loss of 90% of duplicated genes. There is evidence that indicates that part of this selective conservation of gene pairs is compelling to yeast facultative metabolism. As an example, the duplicated NADP-glutamate dehydrogenase pathway has been maintained because of the differential expression of the paralogous GDH1 and GDH3 genes, and the biochemical specialization of the enzymes they encode. The present work has been aimed to the understanding of the regulatory mechanisms that modulate GDH3 transcriptional activation. Our results show that GDH3 expression is repressed in glucose-grown cultures, as opposed to what has been observed for GDH1, and induced under respiratory conditions, or under stationary phase. Although GDH3 pertains to the nitrogen metabolic network, and its expression is Gln3p-regulated, complete derepression is ultimately determined by the carbon source through the action of the SAGA and SWI/SNF chromatin remodelling complexes. GDH3 carbon-mediated regulation is over-imposed to that exerted by the nitrogen source, highlighting the fact that operation of facultative metabolism requires strict control of enzymes, like Gdh3p, involved in biosynthetic pathways that use tricarboxylic acid cycle intermediates.

Barrier proteins remodel and modify chromatin to restrict silenced domains.

Transcriptionally active and inactive domains are frequently found adjacent to one another in the eukaryotic nucleus. To better understand the underlying mechanisms by which domains maintain opposing transcription patterns, we performed a systematic genomewide screen for proteins that may block the spread of silencing in yeast. This analysis identified numerous proteins with efficient silencing blocking activities, and some of these have previously been shown to be involved in chromatin dynamics. We isolated subunits of Swi/Snf, mediator, and TFIID, as well as subunits of the Sas-I, SAGA, NuA3, NuA4, Spt10p, Rad6p, and Dot1p complexes, as barrier proteins. We demonstrate that histone acetylation and chromatin remodeling occurred at the barrier and correlated with a block to the spread of silencing. Our data suggest that multiple overlapping mechanisms were involved in delimiting silenced and active domains in vivo.

Gcn4 negatively regulates expression of genes subjected to nitrogen catabolite repression.

It has been considered that three key elements participate in nitrogen catabolite repression (NCR) of Saccharomyces cerevisiae: the GLN3 and GAT1/NIL1-encoded transcriptional activators and their negative regulator Ure2. The fact that expression of various NCR-sensitive genes is not derepressed in the absence of Ure2 has led to the proposition that there must exist a protein with a similar function to that of Ure2. The results presented in this paper show that various NCR-sensitive genes are derepressed through GLN3-mediated transcriptional activation in a gcn4Delta mutant. This effect is additive to that exerted by the lack of Ure2 and to that evoked in rapamycin-treated cultures. Our results uncover the fact that NCR is not solely achieved through the action of Gln3, Gat1, and Ure2. Since Gcn4 regulates the expression of a broad spectrum of genes, the lack of this transcriptional activator could prevent the expression of a potential Gln3 antagonist. Alternatively, Gcn4 could directly hinder Gln3 functioning.

Influencia de la alimentación en la prevalencia de desnutrición en preescolares de escuelas públicas y privadas del distrito IV de la ciudad de La Paz, gestión 2002 / Influence of the feeding on the frecuency of malnutrition in preschool children of the public and private schools of the district IV of the city of La Paz, management 2002

El objetivo principal de esta investigación es el conocer el grado de relación entre calidad de aliemntación y desnutrición en niños preescolares en las escuelas públicas y privadas del Distrito IV de la Ciudad de La Paz-Bolivia en la gestión 2002. Tambien es el de determinar si existe alguna diferencia en el tipo de alimentación en los niños. Obtener frecuencias de sexo, edad, peso, talla, tipo de escuela, Kilocalirias y proteínas ingeridas en un día en ambos tipos de escuelas. Determinar los porcentajes de niños desnutridos (y el tipo de desnutrición)en cada tipo de escuela. Determinar los porcentajes de baja ingesta de calorias y proteínas en cada tipo de escuela. Relacionar mediante porcentajes la baja ingesta de los dos nutrientes con la presencia de desnitrición en cada tipo de escuela. Clasificación de los niños segun estado nutricional...

Influencia de la alimentación en la frecuencia de desnutrición en preescolares de las escuelas públicas y privadas del distrito III de la ciudad de La Paz, gestión 2002 / Influence of the feeding in the frecuency of pre-scholastic undernoursishment of the school you public and private of district III of the city of La Paz, managemente 2002

El obletivo principal de esta investigación es el conocer el grado de relación entre calidad de aliemntación y desnutrición en niños prresescolares en las escuelas públicas y privadas del Distrito III de la Ciudad de La Paz-Bolivia en la gestión 2002.Tambien es el de determinar siexiate alguna diferencia en el tipo de alimentación en los niños. Optener frecuencias de sexo, edad, peso, talla, tipo de escuela, Kilocalirias y proteínas ingeridas en un día en ambos tipos de escuelas. Determinar los porcentajes de niños desnutridos (y el tipo de desnutrición)en cad tipo de escuela. Determinar los porcentajes de baja ingesta de calorias y proteínas en cada tipo de escuela. Relacionar mediante porcentajes la baja ingesta de los dos nutrientes con la presencia de desnitrición en cada tipo de escuela. Clasificación de los niños segun estado nutricional.

Pathways for glutamate biosynthesis in the yeast Kluyveromyces lactis.

Purified glutamate synthase (GOGAT) from Kluyveromyces lactis was characterized as a high-molecular-mass polypeptide, a distinction shared with previously described GOGATs from other eukaryotic micro-organisms. Using degenerate deoxyoligonucleotides, designed from conserved regions of the alfalfa, maize and Escherichia coli GOGAT genes, a 300 bp PCR fragment from the K. lactis GOGAT gene KIGLT1 was obtained. This fragment was used to construct null GOGAT mutants of K. lactis by gene replacement. These mutants showed no growth defect phenotype and were able to grow on ammonium as sole nitrogen source. Double mutants obtained from a cross between a previously described KIGDH1 mutant and the K. lactis null GOGAT strain were full glutamate auxotrophs. These results indicate that glutamate biosynthesis in K. lactis is afforded through the combined action of KIGDH1 and KIGLT1 products.