Journal
SYSTEMATIC BIOLOGY
Volume 59, Issue 2, Pages 212-225Publisher
OXFORD UNIV PRESS
DOI: 10.1093/sysbio/syp104
Keywords
Evolutionary models; lateral gene transfer; thymidylate synthase
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Funding
- Tel-Aviv University
- Killam postdoctoral fellowship
- Ministry of Science and Technology of the State of Israel
- Ministry of Foreign Affairs
- Ministry of National Education and Research of France
- Israel Science Foundation [1208/04]
- Israeli Ministry of Science
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Thymidylate synthases (Thy) are key enzymes in the synthesis of deoxythymidylate, 1 of the 4 building blocks of DNA. As such, they are essential for all DNA-based forms of life and therefore implicated in the hypothesized transition from RNA genomes to DNA genomes. Two evolutionally unrelated Thy enzymes, ThyA and ThyX, are known to catalyze the same biochemical reaction. Both enzymes are sporadically distributed within each of the 3 domains of life in a pattern that suggests multiple nonhomologous lateral gene transfer (LGT) events. We present a phylogenetic analysis of the evolution of the 2 enzymes, aimed at unraveling their entangled evolutionary history and tracing their origin back to early life. A novel probabilistic evolutionary model was developed, which allowed us to compute the posterior probabilities and the posterior expectation of the number of LGT events. Simulation studies were performed to validate the model's ability to accurately detect LGT events, which have occurred throughout a large phylogeny. Applying the model to the Thy data revealed widespread nonhomologous LGT between and within all 3 domains of life. By reconstructing the ThyA and ThyX gene trees, the most likely donor of each LGT event was inferred. The role of viruses in LGT of Thy is finally discussed.
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