RESUMO
A molecular clone containing the complete sequence of a mitochondrial circular plasmid-like DNA (the R plasmid) isolated from the date-palm variety V3DP was used as a probe in Southern analyses of mitochondrial DNA prepared from other varieties. Another circular structure (the S plasmid) was detected in some of these varieties, and sequenced from variety V2DP. It appears that the R plasmid could have arisen from the S plasmid by an intermolecular recombination event at a set of 26-bp imperfect short direct repeats.
Assuntos
DNA Mitocondrial/genética , DNA de Plantas/genética , Plantas/genética , Recombinação Genética , Sequência de Bases , DNA Circular/genética , Dados de Sequência Molecular , Plasmídeos/genética , Sequências Repetitivas de Ácido Nucleico , Homologia de Sequência do Ácido NucleicoRESUMO
We report here the identification and characterization of two minicircular plasmid-like DNAs isolated from mitochondria of a moroccan date-palm variety. Both molecules were cloned and used as probes in Southern analyses of mitochondrial and total-cellular DNA. Evidence was obtained that these plasmid-like DNAs cross-hybridized but did not show any homology to nuclear, chloroplastic, or main mitochondrial genomes. Sequence analysis revealed that both minicircles, 1,346- and 1,160-bp long, share several stretches of homology, the most important consisting of three identical clusters of lengths 42, 47 and 38 bp. In contrast, no major homology was observed with the other higher-plant plasmid-like DNAs reported so far. Sequence analysis also revealed the presence, in the same strand of one of the minicircles, of two open reading frames potentially encoding proteins 89 and 86 amino acids in length. Interestingly, Northern analyses, using single strands of each minicircle as probes, showed the presence of two transcripts hybridizing only with the strand bearing these two open reading frames. However, computer-assisted comparison of the predicted polypeptide sequences with a protein-sequence library failed to detect any significant homology to known sequences.
Assuntos
DNA Mitocondrial/química , DNA de Plantas/química , Frutas/genética , Plasmídeos/química , Árvores/genética , Sequência de Bases , Northern Blotting , Southern Blotting , Clonagem Molecular , DNA Mitocondrial/isolamento & purificação , DNA de Plantas/biossíntese , DNA de Plantas/isolamento & purificação , Dados de Sequência Molecular , Fases de Leitura Aberta , Plasmídeos/isolamento & purificação , RNA de Plantas/análise , RNA de Plantas/biossíntese , Mapeamento por Restrição , Homologia de Sequência do Ácido Nucleico , Transcrição GênicaRESUMO
Several monomers (177 bp) of a tandemly arranged repetitive nuclear DNA sequence of Brassica oleracea have been cloned and sequenced. They share up to 95% homology between one another and up to 80% with other satellite DNA sequences of Cruciferae, suggesting a common ancestor. Both strands of these monomers show more than 50% homology with many tRNA genes; the best homologies have been obtained with Lys and His yeast mitochondrial tRNA genes (respectively 64% and 60%). These results suggest that small tandemly repeated DNA sequences of plants may have evolved from a tRNA gene ancestor. These tandem repeats have probably arisen via a process involving reverse transcription of polymerase III RNA intermediates, as is the case for interspersed DNA sequences of mammalians. A model is proposed to explain the formation of such small tandemly repeated DNA sequences.
