RESUMO
The synthesis of a relatively homogeneous RNA fraction was observed in germinating wheat embryo. The fraction synthesised within the first 3 h of germination had a high molecular weight (approx. 2.10(6)) and a specific nucleotide composition. In particular, the UMP content was unusually high (47 mol%). The high UMP content resulted probably from the presence of UMP-rich regions within the newly-synthesised polynucleotide chain. Neither ribosomal nor transfer DNA sequences were transcribed at the same time. It is suggested that the newly-synthesised RNA fraction represents an mRNA precursor and is transcribed in the immediate response of wheat embryo to the environmental stimuli to germinate.
Assuntos
Plantas/metabolismo , RNA/biossíntese , Transcrição Gênica , Sequência de Bases , Peso Molecular , Hibridização de Ácido Nucleico , RNA/isolamento & purificação , Triticum/metabolismo , Nucleotídeos de Uracila/análiseRESUMO
A UMP-rich RNA fraction was separated from the bulk cellular RNA by affinity chromatography of wheat embryo total RNA. The obtained preparation was heterogeneous and contained polyribonucleotide chain segments which were resistant to RNAase T1 and consisted mainly of UMP residues (87 mol%). The UMP-rich segments were of various sizes, including large oligonucleotides and polynucleotides (up to approx. 150 nucleotides in length). The oligo(U)- and poly(U)-containing RNA fraction occurred in a low amount (approx. 1% of total RNA) both in dry and germinating wheat embryos. However, at the onset of germination, labelled precursors were preferentially incorporated into the UMP-rich RNA species. The early-synthesized RNA appeared and underwent a considerable degradation within the cell nuclei. It is assumed that both delayed maturation of structural gene transcripts and rapid transcription of regulatory gene units during initial germination stages contribute to the transient abundance of newly made UMP-rich RNA in the early wheat embryos.
Assuntos
Precursores de Ácido Nucleico/metabolismo , Oligonucleotídeos , Oligorribonucleotídeos , Poli U , RNA/metabolismo , Triticum/metabolismo , Nucleotídeos de Uracila , Sequência de Bases , Núcleo Celular/metabolismo , Citoplasma/metabolismoRESUMO
Recent reports indicate that minichromosomes and other small genetic entities may occur in the nuclei of uninfected higher plants. They become especially abundant under some special growth conditions and, sometimes, resemble extrachromosomal genes of ciliated protozoa. An example of such gene-sized DNA species was isolated from resting wheat embryos. The presence of telomeric sequences at its termini and the ability to replicate autonomously in wheat nuclei made it possible to distinguish this nuclear minichromosome from chromosomal DNA fragmentation products. The biological significance of plant minichromosomes remains to be elucidated.
Assuntos
DNA de Plantas/genética , Plantas/genética , Núcleo Celular/genética , Dados de Sequência MolecularRESUMO
A fragment of wheat nuclear DNA was shown to be able to replicate autonomously in wheat nuclei. The fragment was 637-bp long and contained telomeric repeats at both termini. Its replication was manifested by the appearance of a radioactive reaction product of the same approximate size. Further analyses showed that the linear, double-stranded reaction product was labelled along its entire length and contained the same number of similarly located HaeIII sites as did the fragment tested. Prokaryotic DNA remained unlabelled under the same assay conditions.
Assuntos
Sequência de Bases/genética , Replicação do DNA , DNA de Plantas/genética , Triticum/genética , Núcleo Celular/genética , Dados de Sequência MolecularRESUMO
A hypothesis underlying the significance of cytoplasmic events in the process of DNA transposition is proposed. To appear at a new chromosomal site, the transposon sequence is assumed to be first transcribed and then, in a form of the RNA copy, transported to the cytoplasm. A translation-dependent selection of RNA transcripts for reverse transcription is then made and the resulting single-stranded DNA copies return to the nucleus. The free copy may integrate within a new, transcriptionally inactive region of the chromosomal DNA. As a net result, cell differentiation advances in a manner coupled to the message utilization. The hypothesis finds support in many observations, particularly those made for plant cells.
Assuntos
Diferenciação Celular , Elementos de DNA Transponíveis , DNA/genética , Regulação da Expressão Gênica , DNA Polimerase Dirigida por RNA/genética , Recombinação GenéticaRESUMO
One of the large subunits (220 000 daltons) of the wheat embryo RNA polymerase II was demonstrated to undergo phosphorylation with [gamma-32P]ATP in a reaction catalysed by a homologous protein kinase preparation. The same subunit was also observed to be phosphorylated in vivo, at the onset of germination. The phosphorylation resulted in a moderate increase of the RNA polymerase activity.
Assuntos
RNA Polimerases Dirigidas por DNA/metabolismo , RNA Polimerase II/metabolismo , Triticum/enzimologia , Autorradiografia , Técnicas de Cultura , Eletroforese em Gel de Poliacrilamida , Radioisótopos de Fósforo , Fosforilação , Proteínas Quinases/isolamento & purificação , RNA , RNA Polimerase II/isolamento & purificaçãoAssuntos
Etanol , Nucleotídeos de Uracila , Fenômenos Químicos , Química , Plantas/enzimologia , Triticum/enzimologiaAssuntos
DNA , Nucleotídeos , Purinas , Timo , Fosfatase Alcalina , Animais , Bovinos , Fenômenos Químicos , Química , Cromatografia DEAE-Celulose , DNA/análise , Escherichia coli/enzimologia , Hidrazinas , Concentração de Íons de Hidrogênio , Nucleotídeos/análise , Fosfatos , Monoéster Fosfórico Hidrolases , Purinas/análise , Pirimidinas , Serpentes , Espectrofotometria , Raios Ultravioleta , PeçonhasAssuntos
Amidoidrolases , Plantas/enzimologia , Amidoidrolases/isolamento & purificação , Aminoácidos , Carbamatos , Fenômenos Químicos , Precipitação Química , Química , Cromatografia em Gel , Cromatografia por Troca Iônica , Estabilidade de Medicamentos , Concentração de Íons de Hidrogênio , Cinética , Métodos , Peso Molecular , Ácido Orótico , Pirimidinas , TemperaturaAssuntos
Amidoidrolases , Plantas/enzimologia , Amidoidrolases/isolamento & purificação , Aminoácidos , Carbamatos , Fenômenos Químicos , Precipitação Química , Química , Cromatografia em Gel , Cromatografia por Troca Iônica , Estabilidade de Medicamentos , Concentração de Íons de Hidrogênio , Cinética , Métodos , Peso Molecular , Pirimidinas , TemperaturaRESUMO
A procedure developed originally for selective extraction of viral (extrachromosomal) DNA from virus-infected mammalian cells was applied to cell nuclei isolated from uninfected wheat embryos. The resulting nuclear extrachromosomal DNA (exDNA) was enriched for telomere-type sequences by isopycnic centrifugation and inserted into the Sma I site of pUC119. A cloned DNA fragment (241 bp) was found to consist primarily of tandemly repeated heptamere units of the same sequence (5'-CCCTAAA-3') that is known to predominate in telomeric DNA of Arabidopsis thaliana. Hybridization experiments indicate that extrachromosomal telomeric repeats are abundant in resting embryos and disappear rapidly during germination.
Assuntos
DNA de Plantas/genética , Sequências Repetitivas de Ácido Nucleico/genética , Telômero/genética , Triticum/genética , Arabidopsis/genética , Sequência de Bases , Clonagem Molecular , DNA de Plantas/análise , DNA de Plantas/isolamento & purificação , Dados de Sequência Molecular , Sementes/químicaRESUMO
Newly-synthesized cytoplasmic non-mitochondrial DNA was isolated from wheat embryos which had been germinated in the presence of [14C]-thymidine for a time period not long enough to trigger the first post-dormant round of the nuclear DNA replication. This extrachromosomal DNA fraction consisted of linear single-stranded polydeoxyribonucleotide chains, corresponding in size to approximately 1.1 X 10(6) daltons, and amounted to about 0.5% of the total cellular DNA content. It is suggested that the appearance of the newly-synthesized polydeoxyribonucleotide chains in the cytoplasm may be a physiological signal for the initiation of the nuclear DNA replication in germinating wheat embryo cells.
Assuntos
DNA de Cadeia Simples/isolamento & purificação , Triticum/genética , Centrifugação com Gradiente de Concentração , Cromatografia , Citoplasma/análise , Herança Extracromossômica , Hidroxiapatitas , Diester Fosfórico Hidrolases/metabolismo , Sementes/análiseRESUMO
The effect of ethanol on the activity of acid phosphatase from wheat germ was studied, by using ribonucleoside monophosphates as the enzyme substrates. The nucleotides were effectively degraded to the corresponding nucleosides in the presence of ethanol at all concentrations tested, including a 96% (v/v) solution. However, the nucleotide dephosphorylation was accompanied by the liberation of orthophosphate only when the concentration of ethanol in the assay mixture did not exceed 15%. No inorganic phosphate was liberated when ethanol was present at higher concentrations. Instead, monoethyl phosphate was formed in quantities expected for orthophosphate. The results are explained in terms of phosphatase-catalysed alcoholysis.