Thermal melting and circular dichroism of DNA complexes with (Lys-Ala-Ala)10 and (Lys-Ala-Ala)n: effect of polypeptide chain length

DNA complexes with polypeptides (Lys-Ala-Ala)₁)] and (Lys-Ala-Ala)₃₄ have been studied using the methods of thermal melting and circular dichroism. Derivative melting curves of (Lys-Ala-Ala)₁₀ DNA differed substantially from those of (Lys-Ala-Ala)₃₄ prepared either by salt gradient dialysis or by direct mixing. Melting curves of the former complex were unimodal or bimodal with T_m increasing continuously withn input lysin-to-DNA phosphate ratio (r); those of the latter complex consisted of three separate transitions with T_m values almost independent of r. Complete reversibility of binding in the (Lys-Ala-Ala)₁₀-DNA system but a slow redistribution of (Lys-Ala-Ala)₃₄ on DNA at low temperature were found in the redistribution experiments Much faster redistribution from denatured to native DNA occurs at the temperature of melting, contributing to the unusual trimodal melting pattern. Circular dichroism curves are very similar for both complexes and indicate little change of DNA conformation upon polypeptide binding.     

Is ageing the result of dominant and co-dominant mutations?

A number of unexplained features of ageing can be accounted for if cellular ageing is due to dominant or co-dominant mutations. The experimental evidence both for and against this hypothesis is weak, but experiments involving direct testing are possible.     

Atomic Force Microscopy in Imaging of Viruses and Virus-Infected Cells

Summary: Atomic force microscopy (AFM) can visualize almost everything pertinent to structural virology and at resolutions that approach those for electron microscopy (EM). Membranes have been identified, RNA and DNA have been visualized, and large protein assemblies have been resolved into component substructures. Capsids of icosahedral viruses and the icosahedral capsids of enveloped viruses have been seen at high resolution, in some cases sufficiently high to deduce the arrangement of proteins in the capsomeres as well as the triangulation number (T). Viruses have been recorded budding from infected cells and suffering the consequences of a variety of stresses. Mutant viruses have been examined and phenotypes described. Unusual structural features have appeared, and the unexpectedly great amount of structural nonconformity within populations of particles has been documented. Samples may be imaged in air or in fluids (including culture medium or buffer), in situ on cell surfaces, or after histological procedures. AFM is nonintrusive and nondestructive, and it can be applied to soft biological samples, particularly when the tapping mode is employed. In principle, only a single cell or virion need be imaged to learn of its structure, though normally images of as many as is practical are collected. While lateral resolution, limited by the width of the cantilever tip, is a few nanometers, height resolution is exceptional, at approximately 0.5 nm. AFM produces three-dimensional, topological images that accurately depict the surface features of the virus or cell under study. The images resemble common light photographic images and require little interpretation. The structures of viruses observed by AFM are consistent with models derived by X-ray crystallography and cryo-EM.     

Transforming growth factor-beta alters differentiation in cultures of avian neural crest-derived cells: effects on cell morphology, proliferation, fibronectin expression, and melanogenesis.

Neural crest cell differentiation is responsive to a variety of extrinsic signals that include extracellular matrix (ECM) molecules and growth factors. Transforming growth factor-beta (TGF-beta) has diverse, cell type-specific effects, many of which involve regulation of synthesis of ECM molecules and their cell surface receptors. We are studying both separate and potentially interrelated influences of ECM and growth factors on crest differentiation and report here that TGF-beta alters several aspects of crest cell behavior in vitro. Clusters of quail neural crest cells were cultured in the presence and absence of 400 pM TGF-beta 1 and examined at 1, 3, and 5 days. When examined at 5 days, there was a dramatic decrease in the number of melanocytes in treated cultures, regardless of the onset or duration of TGF-beta treatment. With continuous TGF-beta treatment, or with treatment only during crest cluster formation on explanted neural tubes, many cells increased in area, becoming extremely flat. These changes were evident beginning on Day 3. While quantitative analyses of video images documented the size increase, several aspects of motility were relatively unchanged. Synthesis of fibronectin (FN) by approximately 11% of cells on Day 3 and 31% of cells on Day 5 was demonstrated by immunocytochemistry and was associated with a sixfold increase in FN mRNA by Day 5. Experiments which correlated FN immunoreactivity with incorporation of bromodeoxyuridine suggested that the population of large, flat, FN-positive cells did not proliferate selectively and that there was a slower rate of proliferation in TGF-beta-treated cultures than in untreated cultures. The large FN-immunoreactive cells resemble cells derived from cephalic neural crest and raise interesting questions concerning potential roles for TGF-beta in regulating crest differentiation in vivo.     

Some meteorological conditions associated with forest fires in Galicia (Spain)

The present paper offers data on the effect of certain meteorological parameters on the outbreak of forest fires in Galicia (Spain). In a day-to-day analysis, the values of the stability of the air column and the saturation deficit at the lower levels are related to the number of fires occurring in the following 24 h.     

Continuous-flow solid-phase synthesis of potential antigenic peptides of hepatitis B virus

The synthesis of three hepatitis B surface antigens derived from S and pre-S proteins (adw S(140-147), [Tyr148] adw S(139-148), and adw pre-S(120-145)) has been accomplished by the continuous flow Fmoc-polyamide solid phase method. The use of different scavengers and trimethylsilyl bromide (TMSBr) in trifluoroacetic acid as deprotecting procedures is discussed.