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Bacterial toxin-antitoxin (TA) systems serve a variety of physiological functions including regulation of cell growth and maintenance of foreign genetic elements. Sequence analyses suggest that TA families are linked by complex evolutionary relationships reflecting likely swapping of functional domains between different TA families. Our crystal structures of Phd-Doc from bacteriophage P1, the HigA antitoxin from Escherichia coli CFT073, and YeeU of the YeeUWV systems from E. coli K12 and Shigella flexneri confirm this inference and reveal additional, unanticipated structural relationships. The growth-regulating Doc toxin exhibits structural similarity to secreted virulence factors that are toxic for eukaryotic target cells. The Phd antitoxin possesses the same fold as both the YefM and NE2111 antitoxins that inhibit structurally unrelated toxins. YeeU, which has an antitoxin-like activity that represses toxin expression, is structurally similar to the ribosome-interacting toxins YoeB and RelE. These observations suggest extensive functional exchanges have occurred between TA systems during bacterial evolution.
Pubmed ID: 20696400
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Software integrated tool for conducting automatic and manual sequence alignment, inferring phylogenetic trees, mining web based databases, estimating rates of molecular evolution, and testing evolutionary hypotheses. Used for comparative analysis of DNA and protein sequences to infer molecular evolutionary patterns of genes, genomes, and species over time. MEGA version 4 expands on existing facilities for editing DNA sequence data from autosequencers, mining Web-databases, performing automatic and manual sequence alignment, analyzing sequence alignments to estimate evolutionary distances, inferring phylogenetic trees, and testing evolutionary hypotheses. MEGA version 6 enables inference of timetrees, as it implements RelTime method for estimating divergence times for all branching points in phylogeny.
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