RESUMO
The L5 ribosomal protein gene (rpl5) and a S14 ribosomal protein pseudogene were identified by sequence analysis in the potato mitochondrial genome. The two genes are separated by one nucleotide and are found upstream of the apocytochrome b gene (cob), an arrangement conserved also in Arabidopsis and Brassica. The rpl5 gene has an intact open reading frame while the rps14 locus is disrupted by a five nucleotide duplication that introduces a frameshift in the reading frame. Editing of rpl5 and pseudorps14 cotranscripts has been studied by cDNA sequence analysis. Eight C residues are edited into U in the rpl5 coding region, resulting in eight amino acid changes that increase the homology between potato and other RPL5 polypeptides. Interestingly, the rps14 pseudogene sequence is not edited at any nucleotide position.
Assuntos
Genes de Plantas/genética , Pseudogenes/genética , Proteínas Ribossômicas/genética , Solanum tuberosum/genética , Sequência de Aminoácidos , Apoproteínas/genética , Sequência de Bases , Grupo dos Citocromos b/genética , Citocromos b , DNA Mitocondrial/genética , DNA de Plantas/genética , Mitocôndrias , Dados de Sequência Molecular , Fases de Leitura Aberta/genética , RNA/análise , Edição de RNA/fisiologia , RNA Mitocondrial , RNA de Plantas/análise , Mapeamento por Restrição , Análise de Sequência de DNARESUMO
The structure and expression of the potato mitochondrial gene rps10, encoding ribosomal protein S10, has been characterized. The RPS10 polypeptide of 129 amino acids is encoded by two exons of 307 bp and 80 bp respectively, which are separated by a 774-bp class-II intron. Editing of the complete rps10 coding region was studied by sequence analysis of spliced cDNAs. Four C residues are edited into U, resulting in the creation of a putative translational initiation codon, a new stop codon which eliminated ten carboxy-terminal residues, and two additional amino-acid alterations. All these changes increase the similarity between the potato and liverwort polypeptides. One additional C-to-U RNA editing event, observed in the intron sequence of unspliced cDNAs, improves the stability of the secondary structure in stem I (i) of domain I and may thus be required for the splicing reaction. All spliced cDNAs, and most unspliced cDNAs, were completely edited, suggesting that editing is an early step of rps10 mRNA processing and precedes splicing. Earlier work on potato rps10 (Zanlungo et al. 1994) is now known to comprise only a partial analysis of the gene, since the short downstream exon was not identified.
Assuntos
Proteínas de Plantas/genética , Edição de RNA/genética , Splicing de RNA/genética , Proteínas Ribossômicas/genética , Solanum tuberosum/genética , Solanum tuberosum/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Códon/genética , Primers do DNA/genética , DNA Complementar/genética , DNA Mitocondrial/genética , DNA de Plantas/genética , Éxons , Genes de Plantas , Íntrons , Dados de Sequência Molecular , Conformação de Ácido Nucleico , RNA de Plantas/química , RNA de Plantas/genética , RNA de Plantas/metabolismo , Homologia de Sequência de Aminoácidos , Transcrição GênicaRESUMO
The S10 ribosomal protein gene (rps10), which has not been previously reported in any angiosperm mitochondrial genome, was identified by sequence analysis in the potato mitochondrial DNA. This gene is found downstream of a truncated non-functional apocytochrome b (cob) pseudogene, and is expressed as multiple transcripts ranging in size from 0.8 to 5.0 kb. Southern hybridization analysis indicates that rps10-homologous sequences are not present in the wheat mitochondrial genome. Sequence analysis of a single-copy region of the pea mitochondrial genome located upstream of cox1 [11] shows that a non-functional rps10 pseudogene is present in this species. These results suggest that the functional genes coding for wheat and pea mitochondrial RPS10 polypeptides have been translocated to the nucleus.