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The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes

Many cases of nonstandard genetic codes are known in mitochondrial genomes. We carry out analysis of phylogeny and codon usage of organisms for which the complete mitochondrial genome is available, and we determine the most likely mechanism for codon reassignment in each case. Reassignment events ca...

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Autores principales: Sengupta, Supratim, Yang, Xiaoguang, Higgs, Paul G.
Formato: Texto
Lenguaje:English
Publicado: Springer-Verlag 2007
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1894752/
https://www.ncbi.nlm.nih.gov/pubmed/17541678
http://dx.doi.org/10.1007/s00239-006-0284-7
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author Sengupta, Supratim
Yang, Xiaoguang
Higgs, Paul G.
author_facet Sengupta, Supratim
Yang, Xiaoguang
Higgs, Paul G.
author_sort Sengupta, Supratim
collection PubMed
description Many cases of nonstandard genetic codes are known in mitochondrial genomes. We carry out analysis of phylogeny and codon usage of organisms for which the complete mitochondrial genome is available, and we determine the most likely mechanism for codon reassignment in each case. Reassignment events can be classified according to the gain-loss framework. The “gain” represents the appearance of a new tRNA for the reassigned codon or the change of an existing tRNA such that it gains the ability to pair with the codon. The “loss” represents the deletion of a tRNA or the change in a tRNA so that it no longer translates the codon. One possible mechanism is codon disappearance (CD), where the codon disappears from the genome prior to the gain and loss events. In the alternative mechanisms the codon does not disappear. In the unassigned codon mechanism, the loss occurs first, whereas in the ambiguous intermediate mechanism, the gain occurs first. Codon usage analysis gives clear evidence of cases where the codon disappeared at the point of the reassignment and also cases where it did not disappear. CD is the probable explanation for stop to sense reassignments and a small number of reassignments of sense codons. However, the majority of sense-to-sense reassignments cannot be explained by CD. In the latter cases, by analysis of the presence or absence of tRNAs in the genome and of the changes in tRNA sequences, it is sometimes possible to distinguish between the unassigned codon and the ambiguous intermediate mechanisms. We emphasize that not all reassignments follow the same scenario and that it is necessary to consider the details of each case carefully. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00239-006-0284-7) contains supplementary material, which is available to authorized users.
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spelling pubmed-18947522007-06-20 The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes Sengupta, Supratim Yang, Xiaoguang Higgs, Paul G. J Mol Evol Article Many cases of nonstandard genetic codes are known in mitochondrial genomes. We carry out analysis of phylogeny and codon usage of organisms for which the complete mitochondrial genome is available, and we determine the most likely mechanism for codon reassignment in each case. Reassignment events can be classified according to the gain-loss framework. The “gain” represents the appearance of a new tRNA for the reassigned codon or the change of an existing tRNA such that it gains the ability to pair with the codon. The “loss” represents the deletion of a tRNA or the change in a tRNA so that it no longer translates the codon. One possible mechanism is codon disappearance (CD), where the codon disappears from the genome prior to the gain and loss events. In the alternative mechanisms the codon does not disappear. In the unassigned codon mechanism, the loss occurs first, whereas in the ambiguous intermediate mechanism, the gain occurs first. Codon usage analysis gives clear evidence of cases where the codon disappeared at the point of the reassignment and also cases where it did not disappear. CD is the probable explanation for stop to sense reassignments and a small number of reassignments of sense codons. However, the majority of sense-to-sense reassignments cannot be explained by CD. In the latter cases, by analysis of the presence or absence of tRNAs in the genome and of the changes in tRNA sequences, it is sometimes possible to distinguish between the unassigned codon and the ambiguous intermediate mechanisms. We emphasize that not all reassignments follow the same scenario and that it is necessary to consider the details of each case carefully. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00239-006-0284-7) contains supplementary material, which is available to authorized users. Springer-Verlag 2007-05-29 2007-06 /pmc/articles/PMC1894752/ /pubmed/17541678 http://dx.doi.org/10.1007/s00239-006-0284-7 Text en © Springer Science+Business Media, LLC 2007
spellingShingle Article
Sengupta, Supratim
Yang, Xiaoguang
Higgs, Paul G.
The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes
title The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes
title_full The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes
title_fullStr The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes
title_full_unstemmed The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes
title_short The Mechanisms of Codon Reassignments in Mitochondrial Genetic Codes
title_sort mechanisms of codon reassignments in mitochondrial genetic codes
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1894752/
https://www.ncbi.nlm.nih.gov/pubmed/17541678
http://dx.doi.org/10.1007/s00239-006-0284-7
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