3 resultados para Negative Freedom

em University of Connecticut - USA


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This study explores Franco-American relations by examining Franco-American stereotypes. When American participants made ratings of what they think the French think of Americans, the results showed that Americans think the French see Americans in a very negative light. Yet, when the French participants rated what they think Americans think of the French, the result was fairly neutral. Both the French and Americans were found to be over-estimating how negatively they are actually viewed by the other group. If Americans think the French view them negatively and vice versa, these beliefs can permeate interpersonal interactions and can have a potentially negative effect. The results suggest that stereotypes play an important role in intergroup interactions and these findings have important implications for Franco-American relations.

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Classical quorum-sensing (autoinduction) regulation, as exemplified by the lux system of Vibrio fischeri, requires N-acyl homoserine lactone (AHL) signals to stimulate cognate transcriptional activators for the cell density-dependent expression of specific target gene systems. For Pantoea stewartii subsp. stewartii, a bacterial pathogen of sweet corn and maize, the extracellular polysaccharide (EPS) stewartan is a major virulence factor, and its production is controlled by quorum sensing in a population density-dependent manner. Two genes, esaI and esaR, encode essential regulatory proteins for quorum sensing. EsaI is the AHL signal synthase, and EsaR is the cognate gene regulator. esaI, DeltaesaR, and DeltaesaI-esaR mutations were constructed to establish the regulatory role of EsaR. We report here that strains containing an esaR mutation produce high levels of EPS independently of cell density and in the absence of the AHL signal. Our data indicate that quorum-sensing regulation in P. s. subsp. stewartii, in contrast to most other described systems, uses EsaR to repress EPS synthesis at low cell density, and that derepression requires micromolar amounts of AHL. In addition, derepressed esaR strains, which synthesize EPS constitutively at low cell densities, were significantly less virulent than the wild-type parent. This finding suggests that quorum sensing in P. s. subsp. stewartii may be a mechanism to delay the expression of EPS during the early stages of infection so that it does not interfere with other mechanisms of pathogenesis.