Collection of Data on Pesticides in Maize and Tomato in Africa: Protocol for Africa Pesticide Residue Survey Study.

Pesticide use has grown rapidly in West Africa over the past decades. Regulatory capacity has not kept pace with the rapid proliferation of pesticide products and on-farm use. As a result, health and environmental impacts from the growing use of pesticides, despite their potential importance to food safety, remain largely unmonitored, underreported, and poorly understood by key stakeholders. This study protocol was the document for conducting a pesticide survey study to identify the most critically emerging pesticides across the Continent of Africa. Multiple countries were selected in this study to represent the north, east, south, and west regions of Africa. Two food commodities, maize and tomato, were chosen to monitor the pesticide level for food safety. This study protocol describes the fieldwork and laboratory work per the standards of Good Laboratory Practices (GLP) and ISO-17025 and US EPA 860 Residue Chemistry Guidelines but the survey study performed was not considered as a GLP or ISO 17025 study. This is because many steps were not able to be closely monitored per the GLP requirements. This protocol describes the requirements for a pesticide residue study in food collected from local markets. This protocol describes the test commodities, sampling methods, sample transfer/shipping, storage stability, sample analysis, sample disposal, and documentation and record keeping.

Nature of the accessible chromatin at a glucocorticoid-responsive enhancer.

To gain a better understanding of the nature of active chromatin in mammals, we have characterized in living cells the various chromatin modification events triggered by the glucocorticoid receptor (GR) at the rat tyrosine aminotransferase gene. GR promotes a local remodeling at a glucocorticoid-responsive unit (GRU) located 2.5 kb upstream of the transcription start site, creating nuclease hypersensitivity that encompasses 450 bp of DNA. Nucleosomes at the GRU occupy multiple frames that are remodeled without nucleosome repositioning, showing that nucleosome positioning is not the key determinant of chromatin accessibility at this locus. Remodeling affects nucleosomes and adjacent linker sequences, enhancing accessibility at both regions. This is associated with decreased interaction of both the linker histone H1 and the core histone H3 with DNA. Thus, our results indicate that nucleosome and linker histone removal rather than nucleosome repositioning is associated with GR-triggered accessibility. Interestingly, GR induces hyperacetylation of histones H3 and H4, but this is not sufficient either for remodeling or for transcriptional activation. Finally, our data favor the coexistence of several chromatin states within the population, which may account for the previously encountered difficulties in characterizing unambiguously the active chromatin structure in living cells.