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Several GntR/FadR transcriptional regulators govern sugar acid metabolism in bacteria. Although effectors have been identified for a few sugar acid regulators, the mode of effector binding is unknown. Even in the overall FadR subfamily, there are limited details on effector-regulator interactions. Here, we identified the effector-binding cavity in Escherichia coli DgoR, a FadR subfamily transcriptional repressor of D-galactonate metabolism that employs D-galactonate as its effector. Using a genetic screen, we isolated several dgoR superrepressor alleles. Blind docking suggested eight amino acids corresponding to these alleles to form a part of the effector-binding cavity. In vivo and in vitro assays showed that these mutations compromise the inducibility of DgoR without affecting its oligomeric status or affinity for target DNA. Taking Bacillus subtilis GntR as a representative, we demonstrated that the effector-binding cavity is similar among FadR subfamily sugar acid regulators. Finally, a comparison of sugar acid regulators with other FadR members suggested conserved features of effector-regulator recognition within the FadR subfamily. Sugar acid metabolism is widely implicated in bacterial colonization and virulence. The present study sets the basis to investigate the influence of natural genetic variations in FadR subfamily regulators on their sensitivity to sugar acids and ultimately on host-bacterial interactions.
Fundamentals of Mechanics is the culmination of our years of experience in research and teaching the subject. It takes into account our close observations of student responses. Furthermore, it is a sincere attempt to make the study of mechanics enjoyable and arouse interest in the subject. Mechanics, as a subject of physics, is taught at BSc and BTech level. Professor Suresh Chandra conceptualized the book to fulfill requirements of science and engineering students of this level. The other two authors put in their extensive effort to give it a shape of a comprehensive textbook. There are chapters on vectors, laws of motion, conservation laws, inverse-square-law forces, harmonic oscillator, theory of relativity and non-inertial reference frames to match the title with the syllabuses of mechanics at different universities. The chapters are supplemented by ample number of exercises and diagrams which would help in better understanding of the subject. Multiple-choice questions and problems are provided at the end of each chapter to test progress after a lesson is taught.
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Chronic constipation can lead to fecal impaction. It can also rarely lead to catastrophic complications like perforation, colonic obstruction, and fecal peritonitis. We report a rare case of stercoral sigmoid colonic perforation with fecal peritonitis and pneumoperitoneum, which was diagnosed on preoperative CT scan.
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