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1.
Biophys Chem ; 124(1): 43-51, 2006 Oct 20.
Artículo en Inglés | MEDLINE | ID: mdl-16831506

RESUMEN

Knowledge of both the packaging of the linear, double-stranded (ds)DNA in bacteriophages and its subsequent release into the bacterial host is vital to our understanding of phage infection. There is now strong evidence that packaging requires a powerful rotary motor fuelled by ATP. From thermodynamic studies, however, it has been proposed that, at least for those viruses with a contractile tail, the dsDNA ejection from the phage head is a relatively simple physical process that does not require cellular energy and is facilitated by the difference in the conditions of the medium in the environments inside and outside the head. In this case, there should be no enthalpic effects associated with the dehiscence of the capsid and no destruction of it or the other structural elements of the phage. For the present study of temperature-induced phage dehiscence, we used a newly discovered phage with a contractile tail, named the Un (unknown) bacteriophage. Evidence is given of its characteristics in terms of ultrastructural morphology, serological parameters, host range and interaction with host cell. These show that, although it has similarities with the T-even phages and, in particular, the DDVI phage, it appears to be a new type. Earlier viscometric studies with it had shown that the temperature-induced release of the capsid dsDNA was completed at 70 degrees C. In the present investigation, a concentrated suspension of purified phage was subjected to pycnometric analysis through the temperature range of 30 to 70 degrees C. This showed that a significant and abrupt increase in the phage partial volume takes place, which remarkably is in the order of threefold. Viscometric measurements over time at 72 degrees C gave a kinetic curve from which evidence it was suggested that the temperature-induced DNA release is similar to a second order phase transition. At the same time, data from differential scanning calorimetry over the same temperature range showed no enthalpic effect. Our results indicate that the ejection of DNA from the capsid tail is driven by an entropy change.


Asunto(s)
Bacteriófagos/genética , ADN Viral/química , ADN/química , Bacteriófagos/ultraestructura , Rastreo Diferencial de Calorimetría , Microscopía Electrónica , Viscosidad
2.
Chem Phys Lipids ; 94(1): 139-43, 1998 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-9721633

RESUMEN

The authors applied differential scanning calorimetry (DSC) for studying the thermodynamic characteristics of DNA-liposome interactions. At the first stage, the melting curves of the 'order-disorder' thermal transition for lipid component and of the 'helix-coil' transition for DNA were obtained. At the second stage, the phase behavior of the DNA-lipid mixture as a function of both components (lipid/DNA ratio) was obtained. The liposome-DNA interaction was investigated comparing the melting curves of the pure components and the mixture.


Asunto(s)
ADN/química , Dimiristoilfosfatidilcolina/química , Liposomas/química , Rastreo Diferencial de Calorimetría , Conformación de Ácido Nucleico , Termodinámica
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