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- Kitamura, Aya, et al.
(author)
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Characterization and Structure of the Aquifex aeolicus Protein DUF752 A BACTERIAL tRNA-METHYLTRANSFERASE (MnmC2) FUNCTIONING WITHOUT THE USUALLY FUSED OXIDASE DOMAIN (MnmC1)
- 2012
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In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 287:52, s. 43950-43960
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Journal article (peer-reviewed)abstract
- Post-transcriptional modifications of the wobble uridine (U34) of tRNAs play a critical role in reading NNA/G codons belonging to split codon boxes. In a subset of Escherichia coli tRNA, this wobble uridine is modified to 5-methylaminomethyluridine (mnm5U34) through sequential enzymatic reactions. Uridine 34 is first converted to 5-carboxymethylaminomethyluridine (cmnm5U34) by the MnmE-Mnm Genzyme complex. The cmnm5U34 is further modified to mnm5U by the bifunctional MnmC protein. In the first reaction, the FAD-dependent oxidase domain (MnmC1) converts cmnm5U into 5-aminomethyluridine (nm5U34), and this reaction is immediately followed by the methylation of the free amino group into mnm5U34 by the S-adenosylmethionine-dependent domain (MnmC2). Aquifex aeolicus lacks a bifunctional MnmC protein fusion and instead encodes the Rossmann-fold protein DUF752, which is homologous to the methyltransferase MnmC2 domain of Escherichia coli MnmC (26% identity). Here, we determined the crystal structure of the A. aeolicus DUF752 protein at 2.5 Å resolution, which revealed that it catalyzes the S-adenosylmethionine-dependent methylation of nm5U in vitro, to form mnm5U34 in tRNA. We also showed that naturally occurring tRNA from A. aeolicus contains the 5-mnm group attached to the C5 atom of U34. Taken together, these results support the recent proposal of an alternative MnmC1-independent shortcut pathway for producing mnm5U34 in tRNAs.
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| 2. |
- Pastene, Luis A., et al.
(author)
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Radiation and speciation of pelagic organisms during periods of global warming : the case of the common minke whale, Balaenoptera acutorostrata
- 2007
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In: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 16:7, s. 1481-1495
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Journal article (peer-reviewed)abstract
- How do populations of highly mobile species inhabiting open environments become reproductively isolated and evolve into new species? We test the hypothesis that elevated ocean-surface temperatures can facilitate allopatry among pelagic populations and thus promote speciation. Oceanographic modelling has shown that increasing surface temperatures cause localization and reduction of upwelling, leading to fragmentation of feeding areas critical to pelagic species. We test our hypothesis by genetic analyses of populations of two closely related baleen whales, the Antarctic minke whale (Balaenoptera bonaerensis) and common minke whale (Balaenoptera acutorostrata) whose current distributions and migration patterns extent are largely determined by areas of consistent upwelling with high primary production. Phylogeographic and population genetic analyses of mitochondrial DNA control-region nucleotide sequences collected from 467 whales sampled in four different ocean basins were employed to infer the evolutionary relationship among populations of B. acutorostrata by rooting an intraspecific phylogeny with a population of B. bonaerensis. Our findings suggest that the two species diverged in the Southern Hemisphere less than 5 million years ago (Ma). This estimate places the speciation event during a period of extended global warming in the Pliocene. We propose that elevated ocean temperatures in the period facilitated allopatric speciation by disrupting the continuous belt of upwelling maintained by the Antarctic Circumpolar Current. Our analyses revealed that the current populations of B. acutorostrata likely diverged after the Pliocene some 1.5 Ma when global temperatures had decreased and presumably coinciding with the re-establishment of the polar-equatorial temperature gradient that ultimately drives upwelling. In most population samples, we detected genetic signatures of exponential population expansions, consistent with the notion of increasing carrying capacity after the Pliocene. Our hypothesis that prolonged periods of global warming facilitate speciation in pelagic marine species that depend on upwelling should be tested by comparative analyses in other pelagic species.
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