RESUMEN
A new type of maize mitochondrial genome has been identified in the male fertile (normal) inbred line A188. It has been named NA (N in the A188 nuclear background). In comparison to previously described maize mitochondrial genomes, it is classified as a new type since the genome contains unique DNA sequences and unique sets of repeated sequences, and has a unique organization. This brings the number of the maize mitochondrial genome types to five of which three are the cytoplasmic male steriles cmsT, cmsC and cmsS and of which two are the male fertile types NA (in this report) and NB (the previously characterized normal genome in the B37 nuclear background).
Asunto(s)
ADN Mitocondrial/genética , Genes de Plantas , Zea mays/genética , Evolución Biológica , Endogamia , Plásmidos , Secuencias Repetitivas de Ácidos Nucleicos , Mapeo RestrictivoRESUMEN
The mitochondrial genome (mtDNA) organization from a fertile revertant line (V3) derived from the maize cytoplasmic male sterile type T (cmsT) callus tissue culture has been determined. We report that the sequence complexity can be mapped on to a circular "master chromosome" of 705 kb which includes a duplication of 165 kb of DNA when compared to its male sterile progenitor. Associated with this event is also a 0.423-kb deletion, which removed the cmsT-associated urf13 gene. As found for the maize normal type (N) and cmsT mitochondrial genomes, the V3 master chromosome also exists as a multipartite structure generated by recombination through repeated sequences.
Asunto(s)
ADN Mitocondrial/genética , Recombinación Genética , Zea mays/genética , Modelos Genéticos , Hibridación de Ácido Nucleico , Secuencias Repetitivas de Ácidos Nucleicos , Mapeo Restrictivo , Zea mays/fisiologíaRESUMEN
The change of phenotype from sterility to fertility for some cmsT callus tissue culture regenerated plants and their progenies has been correlated with changes in their mitochondrial genome. Those changes that have been analyzed here are the result of recombination events. Two different sets of repeated sequences have been found to be involved in those recombination events. The most common one is a recombination through a 127-bp repeat between various independently isolated revertants. The second one is a recombination through a 58-bp repeat. In every case the products of recombination containing the urf13 gene have been deleted.
Asunto(s)
ADN Mitocondrial/genética , Genes , Plantas/genética , Mapeo Restrictivo , Zea mays/genéticaRESUMEN
Reversion of T type cytoplasmic male sterility (cmsT) to fertility is correlated with sequence changes in a 1.5 kb AvaI fragment. This 1.5 kb AvaI fragment is composed of 5' flanking sequences of ATPase subunit 6, one complete open reading frame (ORF 13) and part of the another (ORF 25). The sequence of the 1.5 kb AvaI fragment was compared to the sequences of homologous regions in the N (male fertile) and T revertant V3 mitochondrial DNA. Sequences were found to diverge between ORF 13 and ORF 25 coding regions. To further characterize the transcription of these rearranged sequences, specific probes for ORF 13, ORF 25 and 5' flanking sequences of ATPase 6 were hybridized to Northern blots of N, cmsT and the T revertant V3 and V18 mtRNAs. Each revertant has a single ORF 25 homologous transcript in contrast to the multitranscript pattern in cmsT. ORF 13 homologous transcripts were not detected in either revertant cytoplasm. The loss of ORF 13 and/or altered ORF 25 transcription in the fertile revertants may be responsible for the male fertility and/or toxin resistance in these plants.
Asunto(s)
Plantas/genética , Transcripción Genética , Secuencia de Bases , ADN Mitocondrial/análisis , Fertilidad , Hibridación de Ácido Nucleico , Homología de Secuencia de Ácido NucleicoRESUMEN
H. maydis toxin resistance, and cytoplasmic reversion from sterility to fertility in Zea mays T type cytoplasm are correlated with sequence changes in a 6.6 kb XhoI fragment of T mitochondrial DNA. Comparative Northern blot analysis of N (normal male fertile), and cmsT (cytoplasmic male sterile) mitochondrial RNAs using subclones of the 6.6 kb Xho I region of cmsT as probes, reveals different sized transcripts. In cmsT these RNA coding sequences have been mapped onto a 1.5 kb AvaI fragment completely internal to the 6.6 kb XhoI region. Comparative Southern analysis of AvaI digested mitochondrial DNA from cmsT, N and a T-type cytoplasm which has reverted to fertility (designated V3) (Brettel et al. 1979), positions the RNA coding sequences on a 1.5 kb, 2.1 kb and 2.1 kb fragment respectively. These sequence rearrangements in the fertile T revertants create a novel mtRNA transcript. Southern hybridization experiments of other higher plant mitochondrial DNAs using the 1.5 kb Ava I fragment from cmsT mtDNA as a probe, indicate the presence of homologous sequences.
Asunto(s)
ADN Mitocondrial/genética , Plantas/genética , Citoplasma/metabolismo , Fertilidad , ARN/genética , Homología de Secuencia de Ácido Nucleico , Transcripción Genética , Zea mays/genéticaRESUMEN
The size of the mitochondrial genome from the fertile cytoplasm of maize has been determined by restriction mapping to be 570 kb. The entire sequence complexity of the genome can be represented on a single circular DNA species (the 'master circle'). The presence of reiterated sequences, active in recombination, results in a complex multipartite organisation.
Asunto(s)
ADN Mitocondrial/genética , Zea mays/genética , Secuencia de Bases , Mapeo Cromosómico , Clonación Molecular , Enzimas de Restricción del ADN , ADN Circular/genética , Peso MolecularRESUMEN
The nucleotide sequence of a segment of mtDNA from Rattus norvegicus (rat) which contains the genes for tRNAile, tRNAgln and tRNAf-met has been determined. A detailed comparison has been made between this sequence and the corresponding sequences of mouse, human and bovine mtDNAs with regard to the primary and secondary structure of the tRNA genes, the regions connecting the tRNA genes, and the regions flanking the tRNA genes which code for the carboxyl terminus of URF-1 and the amino terminus of URF-2. No differences were found in the nucleotide sequences of the genes for tRNAile, tRNAgln and tRNAf-met in mtDNAs from three different female lines of rats (SASCO-1, SASCO-2 and Wild-UT) that differ by substitutions of 0.8% to 1.8% of their total nucleotides.
Asunto(s)
ADN Mitocondrial/genética , Aminoacil-ARN de Transferencia/genética , ARN de Transferencia de Metionina , Ratas/genética , Animales , Secuencia de Bases , Bovinos , Femenino , Genes , Humanos , Ratones , Conformación de Ácido Nucleico , Especificidad de la EspecieRESUMEN
Part of the replication origin-containing A+T-rich region of the Drosophila yakuba mtDNA molecule and segments on either side of this region have been sequenced, and the genes within them identified. The data confirm that the small and large rRNA genes lie in tandem adjacent to that side of the A+T-rich region which is replicated first, and establish that a tRNAval gene lies between the two rRNA genes and that URF1 follows the large rRNA gene. The data further establish that the genes for tRNAile, tRNAgln, tRNAf-met and URF2 lie in the order given, on the opposite side of the A+T-rich region to the rRNA genes and, except for tRNAgln, are contained in the opposite strand to the rRNA, tRNAval and URF1 genes. This is in contrast to mammalian mtDNAs where all of these genes are located on the side of the replication origin which is replicated last, within the order tRNAphe, small (12S) rRNA, tRNAval, large (16S) rRNA, tRNAleu, URF1, tRNAile, tRNAgln, tRNAf-met and URF2, and, except tRNAgln, are all contained in the same (H) strand. In D. yakuba URF1 and URF2, the triplet AGA appears to specify an amino acid, which is again different from the situation found in mammalian mtDNAs, where AGA is used only as a rare termination codon.
Asunto(s)
ADN Mitocondrial/genética , Drosophila/genética , Genes , ARN de Transferencia/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Replicación del ADN , Enzimas de Restricción del ADN , Drosophila melanogaster/genética , Ratones , Conformación de Ácido Nucleico , ARN Ribosómico/genética , Especificidad de la EspecieRESUMEN
Mitochondrial DNA (mtDNA) molecules from Drosophila mauritiana, D. melanogaster, and D. simulans contain a single adenine + thymine (A+T)-rich region, which is similarly located in all molecules, but varies in size among these species. Using agarose gel electrophoresis and electron microscopy, a difference in occurrence of one EcoRI site, and a difference in size (approximately 0.7 kb) of the A+T-rich regions was found between mtDNA molecules of flies of two female lines of D. mauritiana. In heteroduplexes constructed between these two kinds of mtDNA molecules, two or three regions of strand separation, each comprising single strands of unequal length, were apparent near the center of the A+T-rich region. Using the structural differences between D. mauritiana mtDNA molecules it was demonstrated the mtDNA of this species is maternally inherited. Differences in length of A+T-rich regions were also found between mtDNA molecules of two geographically separated strains of D. melanogaster, and between mtDNA molecules of two geographically separated strains of D. simulans. However, in both cases, in heteroduplexes constructed between mtDNA molecules of different strains of one species, the A+T-rich regions appeared completely paired.
Asunto(s)
ADN Mitocondrial , Drosophila melanogaster/análisis , Drosophila/análisis , Adenina/análisis , Animales , Secuencia de Bases , Enzimas de Restricción del ADN , Microscopía Electrónica , Especificidad de la Especie , Timina/análisisRESUMEN
Mitochondrial DNA (mtDNA) molecules from species of the genus Drosophila contain a region exceptionally rich in adenine + thymine (A+T). Using agarose gel electrophoresis and electron microscopy, we determined that in the mtDNA molecules of D. melanogaster, D. simulans, D. mauritiana, D. yakuba, D. takahashii, and D. virilis, the A+T-rich regions, which are 5.1, 4.8, 4.6, 1.1, 2.2, and 1.0 kilobase pairs in size, respectively, are at homologous locations relative to various common EcoRI and HindIII cleavage sites. Under conditions highly permissive for base pairing (35% formamide), heteroduplexes were constructed between EcoRI fragments and whole circular molecules of mtDNAs of the above mentioned six species in a variety of combinations. Complete pairing of molecules outside the A+T-rich region was found in all heteroduplexes examined. However, in contrast, A+T-rich regions of the different species failed to pair in all but those combinations of mtDNAs involving the three most closely related species. In heteroduplexes between D. melanogaster and D. simulans, and between D. melanogaster and D. mauritiana mtDNAs, up to 35% of the A+T-rich regions appeared double-stranded. These data indicate that much more extensive divergence of sequences has occurred in A+T-rich regions than in other regions of Drosophila mtDNA molecules.
Asunto(s)
Adenina , ADN Mitocondrial , Drosophila , Timina , Animales , Secuencia de Bases , Enzimas de Restricción del ADN , ADN Circular , Desoxirribonucleasa HindIII , Drosophila melanogaster , Microscopía Electrónica , Ácidos Nucleicos HeterodúplexRESUMEN
The mitochondrial genome of Drosophila melanogaster is a circular DNA molecule of mol wt 12.35 X 10(6) daltons. A single region accounting for approx. 25% of this molecule can be reproducibly differentially denatured presumably because it is rich in adenine and thymine. We have mapped on the circular mitochondrial genome of D. melanogaster the relative positions of this adenine-thymine (A-T) rich region and the sites sensitive to cleavage by the restriction endonuclease EcoRI, using agarose gel electrophoresis and electron microscopy. Digestion of mitochondrial DNA (mtDNA) molecules to completion with EcoRI resulted in the production of four fragments, A, B, C, and D which represent (+/- SD) 58.9 +/- 1.1%, 27.5 +/- 0.8%, 8.9 +/- 0.5%, and 4.5 +/- 0.3%, of the circular genome length, respectively. Fragments produced by EcoRI digestion and circularized by incubation at 2 degrees C also fell into four distinct length groups with means (+/- SD) of 59.1 +/- 0.5%, 27.5 +/- 0.5%, 9.2 +/- 0.3%, and 4.6 +/- 0.2% of the circular genome length. From a consideration of the lengths of fragments resulting from incomplete EcoRI digestion, it was determined that the arrangement of the fragments in the circular genome was A-C-B-D. By electron microscope examination of partially denatured EcoRI fragments, the A-T-rich region was shown to be located in the A fragment closer to one end than to the other. By similar partial-denaturation studies of fragments resulting from incomplete EcoRI digestion, it was determined that, in the circular genome, of the two EcoRI sites which define the limits of the A fragment, the site between the A and D fragment lies nearest to the A-T-rich region.
Asunto(s)
Adenina/análisis , ADN Circular/análisis , ADN Mitocondrial/análisis , Drosophila melanogaster/química , Timina/análisis , Animales , Enzimas de Restricción del ADN , Conformación de Ácido NucleicoRESUMEN
We have determined by electron microscopy the molecular weight of circular mitochondrial DNA (mtDNA) molecules from 39 species representing 13 groups of five subgenera of the genus Drosophila. mtDNA molecules of all species examined, other than members of the melanogaster group, had, with one exception, molecular weights in the rather narrow range 9.90 X 10(6). The one exception was D. robusta, which had a molecular weight of 10.61 X 10(6). In contrast, mtDNA molecules from species within the melanogaster group had molecular weights covering the considerably greater range 9.92 X 10(6) to 12.35 X 10(6). Applying the electron microscope denaturation mapping technique of Inman to mtDNA molecules of eight species of the melanogaster group, we found each of them to contain a region [presumably rich in adenine and thymine (A+T)] which denatured at a specific temperature (40 degrees) at which most of the remainder of the molecule remained undenatured. The size of the A+T-rich region was constant for mtDNA molecules of a species, but varied from 0.62 X 10(6) to 3.41 X 10(6) for mtDNA molecules of different species. It was demonstrated that the differences in molecular weights of the A+T-rich regions can almost completely account for the differences in total molecular weights of the mtDNA molecules from species of the melanogaster group.