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Differential DNA Binding of Transcriptional Regulator PcaU from Acinetobacter sp . Strain ADP1. Roland Popp, 2002.Transcriptional regulator PcaU from Acinetobacter sp . strain ADP1 governs expression of genes for protocatechuate degradation (pca genes) as a repressor or an activator depending on the levels of the inducer protocatechuate and of its own gene . PcaU is a member of the IclR protein family . Here the DNA binding properties of the purified protein are described in terms of the location of the binding sites and the affinity to these sites . Native PcaU was purified after overexpression of the pcaU gene in Escherichia coli . It is a dimer in solution . The binding site in the pcaU-pcaI intergenic region is located between the two divergent promoters covering 45 bp, which includes three perfect 10-bp repetitions . A PcaU binding site downstream of pcaU is covered by PcaU across two palindromic sequence repetitions . The affinity of PcaU for the intergenic binding sites is 50-fold higher (dissociation constant [Kd], 0.16 nM) than the affinity for the site downstream of pcaU (Kd, 8 nM) . The binding of PcaU was tested after modifications of the intergenic binding site . Removal of any external sequence repetition still allowed for specific binding of PcaU, but the affinity was significantly reduced, suggesting an important role for all three sequence repetitions in gene expression . The involvement of DNA bending in the regulatory process is suggested by the observed strong intrinsic curvature displayed by the pcaU-pcaI intergenic DNA . An Improved Enrichment Broth for Isolation of Escherichia coli O157, with Specific Reference to Starved Cells, from Radish Sprouts. Shin Sata, 2003.An enrichment broth was developed for the efficient isolation of Escherichia coli O157 from radish sprouts . The broth was buffered peptone water containing 0.5% sodium thioglycolate (STG-BPW), which was designed to allow growth of E . coli O157 in starved and unstarved states . However, this medium suppressed the growth of non-carbohydrate-fermenting obligate aerobes whose colonial appearance on sorbitol MacConkey agar containing cefixime and tellurite (CT-SMAC) resembled that of E . coli O157 . Both starved and unstarved cells of E . coli O157 experimentally inoculated into radish sprouts were successfully recovered with STG-BPW enrichment in all cases, most of which showed marked disappearance of E . coli O157-like colonies on CT-SMAC .
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