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Survival and Dormancy of Mycobacterium avium subsp . paratuberculosis in the Environment. Richard J. Whittington, 2004.The survival of Mycobacterium avium subsp. paratuberculosis was studied by culture of fecal material sampled at intervals for up to 117 weeks from soil and grass in pasture plots and boxes . Survival for up to 55 weeks was observed in a dry fully shaded environment, with much shorter survival times in unshaded locations . Moisture and application of lime to soil did not affect survival . UV radiation was an unlikely factor, but infrared wavelengths leading to diurnal temperature flux may be the significant detrimental component that is correlated with lack of shade . The organism survived for up to 24 weeks on grass that germinated through infected fecal material applied to the soil surface in completely shaded boxes and for up to 9 weeks on grass in 70% shade . The observed patterns of recovery in three of four experiments and changes in viable counts were indicative of dormancy, a hitherto unreported property of this taxon . A dps-like genetic element and relA, which are involved in dormancy responses in other mycobacteria, are present in the M . avium subsp . paratuberculosis genome sequence, providing indirect evidence for the existence of physiological mechanisms enabling dormancy . However, survival of M . avium subsp . paratuberculosis in the environment is finite, consistent with its taxonomic description as an obligate parasite of animals . Architecture of a Fur Binding Site: a Comparative Analysis. Jennifer L. Lavrrar, 2003.Fur is an iron-binding transcriptional repressor that recognizes a 19-bp consensus site of the sequence 5'-GATAATGATAATCATTATC-3' . This site can be defined as three adjacent hexamers of the sequence 5'-GATAAT-3', with the third being slightly imperfect (an F-F-F configuration), or as two hexamers in the forward orientation separated by one base pair from a third hexamer in the reverse orientation (an F-F-x-R configuration) . Although Fur can bind synthetic DNA sequences containing the F-F-F arrangement, most natural binding sites are variations of the F-F-x-R arrangement . The studies presented here compared the ability of Fur to recognize synthetic DNA sequences containing two to four adjacent hexamers with binding to sequences containing variations of the F-F-x-R arrangement (including natural operator sequences from the entS and fepB promoter regions of Escherichia coli) . Gel retardation assays showed that the F-F-x-R architecture was necessary for high-affinity Fur-DNA interactions and that contiguous hexamers were not recognized as effectively . In addition, the stoichiometry of Fur at each binding site was determined, showing that Fur interacted with its minimal 19-bp binding site as two overlapping dimers . These data confirm the proposed overlapping-dimer binding model, where the unit of interaction with a single Fur dimer is two inverted hexamers separated by a C:G base pair, with two overlapping units comprising the 19-bp consensus binding site required for the high-affinity interaction with two Fur dimers .
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