RESUMEN
RNA editing subsumes a number of functionally different mechanisms which have in common that they change the nucleotide sequence of RNA transcripts such that they become different from what would conventionally be predicted from their gene sequences. RNA editing has now been found in the organelles of numerous organisms as well as in a few nuclear transcripts. Most recently, it was shown to affect tRNAs in the mitochondria of several animals. The occurrence and evolutionary persistence of RNA editing is perplexing since backmutations in the genes might be assumed rapidly to eliminate the need for 'correction' of the gene sequences at the post-transcriptional level. Here, we review the recent RNA editing systems discovered in animal mitochondria and propose that they have arisen as a mechanism counteracting the accumulation of mutations that occurs in asexual genetic system.
Asunto(s)
Mitocondrias/genética , Mitocondrias/fisiología , Edición de ARN/fisiología , Reproducción Asexuada/genética , Animales , Femenino , Masculino , ARN de Transferencia/genéticaRESUMEN
During meiosis, numerous DSBs (double-strand breaks) are induced along the genome which are processed via several steps into crossovers. Crossovers ensure the faithful segregation of homologous chromosomes during meiosis I. Although required for faithful chromosome segregation, DSBs pose a severe hazard to genome integrity. Chromosome segregation in the presence of persisting DSBs can result in loss or missegregation of entire chromosome arms and in the formation of aneuploid gametes, conditions frequently associated with birth defects, still births and cancer susceptibility in offspring. Co-ordination between chromosomal exchange and meiotic cell-cycle progression is achieved via a surveillance mechanism commonly referred to as the recombination checkpoint. Both components of the mitotic DNA damage checkpoint as well as meiosis-specific functions contribute to this highly conserved surveillance system.
Asunto(s)
Cromosomas Fúngicos/genética , Intercambio Genético/genética , Meiosis/genética , Saccharomyces cerevisiae/genética , Daño del ADN/genética , Proteínas Nucleares/metabolismo , Saccharomyces cerevisiae/citologíaRESUMEN
The group II intron bl1, the first intron of the mitochondrial cytochrome b gene in yeast is self-splicing in vitro. Genetic evidence suggests that trans-acting factors are required for in vivo splicing of this intron. In accordance with these findings, we present in vitro data showing that splicing of bl1 under physiological conditions depends upon the presence of proteins of a mitochondrial lysate. ATP is an essential component in this reaction. Overexpression of the nuclear-encoded DEAD box protein pMSS116 results in a marked increase in the ATP-dependent splicing activity of the extract, suggesting that pMSS116 may play an important role in splicing of bl1.
Asunto(s)
Intrones/genética , ARN Helicasas , ARN Nucleotidiltransferasas/fisiología , Empalme del ARN , Proteínas de Unión al ARN/metabolismo , Saccharomyces cerevisiae/genética , Adenosina Trifosfato/metabolismo , Secuencia de Aminoácidos , Grupo Citocromo b/genética , ARN Helicasas DEAD-box , Regulación Fúngica de la Expresión Génica , Genes Fúngicos/genética , Datos de Secuencia Molecular , ARN , ARN Nucleotidiltransferasas/biosíntesis , ARN de Hongos/genética , ARN Mitocondrial , Proteínas de Saccharomyces cerevisiaeRESUMEN
The group II intron bI1, the first intron of the mitochondrial cytochrome b gene in yeast is self-splicing in vitro. Genetic evidence suggests that trans-acting factors are required for in vivo splicing of this intron. In accordance with these findings, we present in vitro data showing that splicing of bI1 under physiological conditions depends upon the presence of proteins of a mitochondrial lysate. ATP is an essential component is this reaction. Overexpression of the nuclear-encoded DEAD box protein pMSS-116 results in a marked increase in the ATP-dependent splicing activity of the extract, suggesting that pMSS116 may play an important role in splicing of bI1.
Asunto(s)
Adenosina Trifosfato/metabolismo , Intrones/genética , ARN Helicasas , ARN Nucleotidiltransferasas/fisiología , Empalme del ARN , Proteínas de Unión al ARN/metabolismo , Saccharomyces cerevisiae/genética , Secuencia de Aminoácidos , Grupo Citocromo b/genética , ARN Helicasas DEAD-box , Regulación Fúngica de la Expresión Génica , Genes Fúngicos/genética , Datos de Secuencia Molecular , ARN Nucleotidiltransferasas/biosíntesis , ARN de Hongos/genética , ARN Mensajero , Proteínas de Saccharomyces cerevisiaeRESUMEN
In the mitochondrial genome of marsupials, the tRNA gene located at the position where in other mammals an aspartyl-tRNA is encoded carries the glycine anticodon GCC. Post-transcriptionally, an RNA editing mechanism affects the second position of the anticodon such that the aspartate anticodon GUC is created in approximately 50% of the mature tRNA pool. We show that the unedited version of this tRNA'Asp' (GCC) can be specifically aminoacylated with glycine in vitro, while the edited version becomes aminoacylated with aspartic acid. Furthermore, we show that both forms are aminoacylated to a substantial extent in vivo. By replacing an amino group with a keto group, RNA editing thus changes the identity of this tRNA allowing a single gene to encode two tRNAs.
Asunto(s)
Zarigüeyas/metabolismo , Edición de ARN , ARN de Transferencia de Aspártico/metabolismo , ARN/metabolismo , Animales , Secuencia de Bases , Glicina/metabolismo , Técnicas In Vitro , Mitocondrias Hepáticas/metabolismo , Datos de Secuencia Molecular , Conformación de Ácido Nucleico , Zarigüeyas/genética , ARN/química , ARN/genética , ARN Mitocondrial , Aminoacil-ARN de Transferencia/genética , Aminoacil-ARN de Transferencia/metabolismo , ARN de Transferencia de Aspártico/química , ARN de Transferencia de Aspártico/genética , ARN de Transferencia de Glicerina/genética , ARN de Transferencia de Glicerina/metabolismoRESUMEN
The trans-splicing group II intron c/d in the Oenothera mitochondrial nad1 gene is modified by RNA editing in domain 6. This C-to-U conversion generates the typical domain 6 structure, which prompted us to speculate that this RNA editing event might be essential for splicing. To test this hypothesis, we investigated the influence of unedited and edited sequences of the Oenothera intron on splicing in vitro. The stem of domain 6 of intron nad1-c/d was transplanted into the autocatalytic yeast intron aI5c, yielding chimeras with the genomic C and the edited U, respectively, 5' of the branchpoint A. When incubated under self-splicing conditions, only the edited chimera was released as a lariat, while the precursor with the genomically coded C remained inactive. Our results support the hypothesis that Oenothera group II intron nad1-c/d cannot be spliced from the primary transcript without previous editing in domain 6.
Asunto(s)
Intrones/genética , Plantas/genética , Edición de ARN , Empalme del ARN , ARN de Planta/genética , Secuencia de Bases , Mitocondrias/genética , Datos de Secuencia Molecular , Conformación de Ácido Nucleico , ARN Catalítico , Saccharomyces cerevisiae/genéticaRESUMEN
Mutations in human mitochondrial tRNA genes are associated with a number of multisystemic disorders. Using an assay that combines tRNA oxidation and circularization we have determined the relative amounts and states of aminoacylation of mutant and wild-type tRNAs in tissue samples from patients with MELAS syndrome (mito- chondrial myopathy, encephalopathy, lactic acidosis, stroke-like episodes) and MERRF syndrome (myoclonus epilepsy with ragged red fibers), respectively. In most, but not all, biopsies from MELAS patients carrying the A3243G substitution in the mitochondrial tRNA(Leu(UUR))gene, the mutant tRNA is under-represented among processed and/or aminoacylated tRNAs. In contrast, in biopsies from MERRF patients harboring the A8344G substitution in the tRNA(Lys)gene neither the relative abundance nor the aminoacylation of the mutated tRNA is affected. Thus, whereas the A3243G mutation may contribute to the pathogenesis of MELAS by reducing the amount of aminoacylated tRNA(Leu), the A8344G mutation does not affect tRNA(Lys)function in the same way.