RESUMO
Long DNA molecules remain difficult to image by atomic force microscopy (AFM) because of their tendency to entanglement and spontaneous formation of networks. We present a comparison of two different DNA deposition methods operating at room temperature and humidity conditions, aimed at reproducible imaging of isolated and relaxed λ DNA conformations by AFM in air. We first demonstrate that a standard deposition procedure, consisting in adsorption of DNA in the presence of divalent cations followed by washing and air-drying steps, yields a coexistence of different types of λ DNA networks with a only a few isolated DNA chains. In contrast, deposition using a spin-coating-based technique results in reproducible coverage of a significant fraction of the substrate area by isolated and relaxed λ DNA molecules, with the added benefit of a reduction in the effect of a residual layer that normally embeds DNA strands and leads to an apparent DNA height closer to the expected value. Furthermore, we show that deposition by spin-coating is also well-suited to visualize DNA-protein complexes. These results indicate that spin-coating is a simple, powerful alternative for reproducible sample preparation for AFM imaging.
Assuntos
Silicatos de Alumínio/química , Bacteriófago lambda/genética , Bacteriófago lambda/ultraestrutura , DNA Viral/química , DNA Viral/ultraestrutura , Microscopia de Força Atômica/métodos , AdsorçãoRESUMO
Human cytomegalovirus (HCMV) is a double-stranded DNA virus with the largest genome (~235 kb) of the known human herpes viruses. The coding potential and transcript structures of most HCMV predicted genes have not been identified. New or unknown genes could exist in clinical strains. The SMART (switching mechanism at 5' end of RNA template of reverse transcriptase) technique was used to construct a full-length cDNA library of an HCMV clinical strain in the late expression phase. Randomly selected clones were sequenced. The sequenced expressed sequence tags were used to identify the expression and transcript structures of some predicted and unpredicted genes of HCMV. The transcripts of the UL99, TRL5/IRL5, UL73 to UL75, UL4, and UL115 genes, which were previously detected, were obtained with full-length structures from this library. Some novel transcripts, including several transcripts of UL/b' genes and three antisense transcripts of UL83, UL87 and UL31 were found. The novel transcripts that were found, particularly the antisense transcripts of UL83, UL87 and UL31, showed that the transcription of HCMV genes is more complex than previously predicted. Our study highlights the usefulness of the full-length cDNA library for discovering new genes and transcripts of HCMV.
Assuntos
Citomegalovirus/genética , DNA Complementar/genética , Biblioteca Gênica , Análise de Sequência de DNA , Sequência de Bases , Mapeamento Cromossômico , DNA Viral/genética , DNA Viral/ultraestrutura , Etiquetas de Sequências Expressas , Expressão Gênica , Humanos , Dados de Sequência Molecular , Fases de Leitura Aberta/genética , Reação em Cadeia da Polimerase , RNA Viral/genéticaRESUMO
OBJECTIVE: Recent studies in peripheral blood mononuclear cells (PBMCs) have indicated that exacerbations of multiple sclerosis (MS) could be associated with the reactivation of latent varicella-zoster virus (VZV). METHODS: Ultrastructural observations for viral particles were made by electron microscopy in cerebrospinal fluid (CSF) from 15 MS patients during relapse, 19 MS patients during remission, and 28 control subjects. Initial findings were reproduced in a confirmation cohort. In addition, DNA from VZV was quantified by real-time polymerase chain reaction in PBMCs and CSF from a large number of MS patients (n = 78). RESULTS: We found by electron microscopy the presence of abundant viral particles identical to VZV in CSF obtained from MS patients within the first few days of an acute relapse. In contrast, viral particles were not seen in CSF samples from MS patients in remission or from neurological control subjects. Also, DNA from VZV was present in CSF and in PBMCs during relapse, disappearing in most patients during remission. The mean viral load was 542 times greater in CSF at relapse than in CSF at remission and 328 times greater in CSF at relapse than in PBMCs at relapse. INTERPRETATION: The ultrastructural finding of viral particles identical to VZV, together with the simultaneous presence of large quantities of DNA from VZV in the subarachnoid space, almost restricted to the periods of exacerbation, as well as its steady diminution and eventual disappearance from clinical relapse to clinical remission are surprising and constitute the strongest evidence to support the participation of VZV in the pathogenesis of MS.
Assuntos
Herpesvirus Humano 3/ultraestrutura , Esclerose Múltipla Recidivante-Remitente/líquido cefalorraquidiano , Esclerose Múltipla Recidivante-Remitente/virologia , Adolescente , Adulto , Idoso , Estudos de Coortes , DNA Viral/líquido cefalorraquidiano , DNA Viral/ultraestrutura , Feminino , Herpesvirus Humano 3/genética , Humanos , Masculino , Pessoa de Meia-Idade , Esclerose Múltipla Recidivante-Remitente/genética , Carga Viral/métodosRESUMO
Little is known about the in vivo assembly pathway or structure of the hepatitis C virus nucleocapsid. In this work the intermediates of HCcAg multimerization in Pichia pastoris cells and the nucleic acid binding properties of structured nucleocapsid-like particles (NLPs) were studied. Extensive cross-linking was observed for HCcAg after glutaraldehyde treatment. Data suggest that HCcAg exists in dimeric forms probably representing P21-P21, P21-P23, and P23-P23 dimers. In addition, the presence of HCcAg species that might represent trimers and multimers was observed. After sucrose equilibrium density gradient purification and nuclease digestion, NLPs were shown to contain both RNA and DNA molecules. Finally, the analysis by electron microscopy indicated that native NLPs were resistant to nuclease treatment. These results indicated that HCcAg assembles through dimers, trimers, and multimers' intermediates into capsids in P. pastoris cells. Assembly of NLPs in its natural environment might confer stability to these particles by adopting a compact structure.
Assuntos
DNA Viral/química , DNA Viral/ultraestrutura , Pichia/metabolismo , RNA Viral/química , RNA Viral/ultraestrutura , Proteínas do Core Viral/química , Proteínas do Core Viral/ultraestrutura , Sítios de Ligação , Proteínas de Ligação a DNA/química , Dimerização , Peso Molecular , Proteínas do Nucleocapsídeo/química , Proteínas do Nucleocapsídeo/genética , Proteínas do Nucleocapsídeo/ultraestrutura , Pichia/genética , Ligação Proteica , Proteínas de Ligação a RNA/química , Proteínas do Core Viral/genéticaRESUMO
El cáncer es un proceso multifactorial y con múltiples etapas. Los protooncogenes, antioncogenes y virus oncogénicos están involucrados en el desarrollo de diversas neoplasias. La expresión alterada de los protooncogenes (por mutaciones, rearreglos o amplificaciones), así como la cooperación entre ellos puede llevar a la célula a una estado transformado. Los genes p53 y RB codifican para dos proteínas antioncogénicas que regulan las decisiones celulares de proliferación o diferenciación. La ausencia de RB (pérdida de ambos alelos) lleva a la liberación de factores de transcripción. p53 en su forma mutada, favorece el crecimiento celular. El cáncer cervicouterino ejemplifica claramente la intervención de este tipo de factores en su desarrollo. Los papilomavirus humanos genitales (PVH) estan implicados en su etiología como iniciadores de la proliferación celular. La inactivación de las proteínas antioncogénicas p53 y p105 RB porparte de los oncogenes virales E6 y E7, respectivamente, mantiene el estado de divición celular continua. Adicionalmente, la participación de ooncogenes expresados en forma alterada (c-myc) y otros cofactores contribuyen a modificar los periodos de latencia y la gravedad de la enfermedad