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Genome Biology and Evolution (1)
Molecular Biology and Evolution (1)
Koonin, Eugene V. (2)
Novichkov, Pavel S. (1)
Ogurtsov, Aleksey Y. (1)
Shabalina, Svetlana A. (1)
Spiridonov, Alexey N. (1)
Spiridonov, Nikolay A. (1)
Wolf, Yuri I. (1)
Year of Publication
A Tight Link between Orthologs and Bidirectional Best Hits in Bacterial and Archaeal Genomes
Wolf, Yuri I.
Genome Biology and Evolution
Orthologous relationships between genes are routinely inferred from bidirectional best hits (BBH) in pairwise genome comparisons. However, to our knowledge, it has never been quantitatively demonstrated that orthologs form BBH. To test this “BBH-orthology conjecture,” we take advantage of the operon organization of bacterial and archaeal genomes and assume that, when two genes in compared genomes are flanked by two BBH show statistically significant sequence similarity to one another, these genes are bona fide orthologs. Under this assumption, we tested whether middle genes in “syntenic orthologous gene triplets” form BBH. We found that this was the case in more than 95% of the syntenic gene triplets in all genome comparisons. A detailed examination of the exceptions to this pattern, including maximum likelihood phylogenetic tree analysis, showed that some of these deviations involved artifacts of genome annotation, whereas very small fractions represented random assignment of the best hit to one of closely related in-paralogs, paralogous displacement in situ, or even less frequent genuine violations of the BBH–orthology conjecture caused by acceleration of evolution in one of the orthologs. We conclude that, at least in prokaryotes, genes for which independent evidence of orthology is available typically form BBH and, conversely, BBH can serve as a strong indication of gene orthology.
orthology; bidirectional best hit; genome comparison; synteny
Distinct Patterns of Expression and Evolution of Intronless and Intron-Containing Mammalian Genes
Shabalina, Svetlana A.
Ogurtsov, Aleksey Y.
Spiridonov, Alexey N.
Novichkov, Pavel S.
Spiridonov, Nikolay A.
Molecular Biology and Evolution
Comparison of expression levels and breadth and evolutionary rates of intronless and intron-containing mammalian genes shows that intronless genes are expressed at lower levels, tend to be tissue specific, and evolve significantly faster than spliced genes. By contrast, monomorphic spliced genes that are not subject to detectable alternative splicing and polymorphic alternatively spliced genes show similar statistically indistinguishable patterns of expression and evolution. Alternative splicing is most common in ancient genes, whereas intronless genes appear to have relatively recent origins. These results imply tight coupling between different stages of gene expression, in particular, transcription, splicing, and nucleocytosolic transport of transcripts, and suggest that formation of intronless genes is an important route of evolution of novel tissue-specific functions in animals.
alternative splicing; intronless genes; monomorphic genes; polymorphic genes; mammalian gene evolution
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