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The Escherichia coli GTPase CgtAE Cofractionates with the 50S Ribosomal Subunit and Interacts with SpoT, a ppGpp Synthetase/Hydrolase. P. Wout, 2004.CgtAE/ObgE/YhbZ is an Escherichia coli guanine nucleotide binding protein of the Obg/GTP1 subfamily whose members have been implicated in a number of cellular functions including GTP-GDP sensing, sporulation initiation, and translation . Here we describe a kinetic analysis of CgtAE with guanine nucleotides and show that its properties are similar to those of the Caulobacter crescentus homolog CgtAC . CgtAE binds both GTP and GDP with moderate affinity, shows high guanine nucleotide exchange rate constants for both nucleotides, and has a relatively low GTP hydrolysis rate . We show that CgtAE is associated predominantly with the 50S ribosomal subunit . Interestingly, CgtAE copurifies with SpoT, a ribosome-associated ppGpp hydrolase/synthetase involved in the stress response . The interaction between CgtAE and SpoT was confirmed by reciprocal coprecipitation experiments and by two-hybrid assays . These studies raise the possibility that the ribosome-associated CgtAE is involved in the SpoT-mediated stress response . Selection of Single-Chain Antibodies against the VP8* Subunit of Rotavirus VP4 Outer Capsid Protein and Their Expression in Lactobacillus casei. Vicente Monedero, 2004. Comparison of Atomic Force Microscopy Interaction Forces between Bacteria and Silicon Nitride Substrata for Three Commonly Used Immobilization Methods. Virginia Vadillo-Rodríguez, 2004.Atomic force microscopy (AFM) has emerged as a powerful technique for mapping the surface morphology of biological specimens, including bacterial cells . Besides creating topographic images, AFM enables us to probe both physicochemical and mechanical properties of bacterial cell surfaces on a nanometer scale . For AFM, bacterial cells need to be firmly anchored to a substratum surface in order to withstand the friction forces from the silicon nitride tip . Different strategies for the immobilization of bacteria have been described in the literature . This paper compares AFM interaction forces obtained between Klebsiella terrigena and silicon nitride for three commonly used immobilization methods, i.e., mechanical trapping of bacteria in membrane filters, physical adsorption of negatively charged bacteria to a positively charged surface, and glutaraldehyde fixation of bacteria to the tip of the microscope . We have shown that different sample preparation techniques give rise to dissimilar interaction forces . Indeed, the physical adsorption of bacterial cells on modified substrata may promote structural rearrangements in bacterial cell surface structures, while glutaraldehyde treatment was shown to induce physicochemical and mechanical changes on bacterial cell surface properties . In general, mechanical trapping of single bacterial cells in filters appears to be the most reliable method for immobilization .
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