Is the siesta an adaptation to disease?

Why does the practice of the siesta vary across human cultures? One explanation is that it is a form of energy conservation in environments with high temperatures and/or agricultural labor. Disease palliation and prevention represents another area where the siesta might be beneficial. A preliminary study used the Human Relations Area Files (HRAF) to examine the characteristics associated with siesta occurrence. Siestas were not statistically associated with high temperatures or agricultural labor (p>.05). They were, however, statistically associated with the occurrence of malaria (p<.05) and marginally associated with parasitic and chronic infectious disease. Preliminary results suggest that siestas could be adaptive in environments with chronic infectious disease.     

A calorimetric approach to the study of the interactions of cytidine-3'-phosphate with bovine seminal ribonuclease

A calorimetric study at 25 degrees C is reported on the interaction between allosteric bovine seminal ribonuclease and cytidine-3'-phosphate. The results are compared with those obtained under identical experimental conditions for the interaction of pancreatic ribonuclease A and the same nucleotide. The analysis of the data provides evidence that the binding sites of seminal ribonuclease for cytidine-3'-phosphate are not equivalent, in agreement with previous equilibrium dialysis studies. A model with two sites with different affinities toward the nucleotide, the site with higher affinity resembling the binding site of pancreatic ribonuclease, is proposed. The values calculated for the thermodynamic parameters provide an insight of the forces involved in the interaction of the two enzymes with the nucleotide.     

Structural and dynamical properties of two DNA oligomers with the same base composition and different sequence.

We compared the structural and dynamical properties of two DNA fragments, 27 bp long, having the same base composition but a different sequence. This work aims to understand how the base sequence on a purine rich strand in a double helix, which is important for many biological functions, is related to structural features and to measurable physical quantities. Structural characterization of the two samples was performed both by conventional spectroscopic methods (circular dichroism and UV denaturation experiments) and by means of a gamma-ray footprinting technique which gives information on fine conformational differences. Dynamical features of the samples were studied by fluorescence polarization anisotropy (FPA) measurements which allow the evaluation of some hydrodynamic parameters, such as the hydrodynamic radius and the elastic torsion constant of DNA. Using a gamma-ray footprinting technique, we observed that the interruption of the long homopurine-homopyrimidine run in the control sample, due to the 'scrambling' operation, alters the DNA three-dimensional structure, also at nucleotide level. Besides, an increase in thermal stability and in the torsional rigidity of the 'scrambled' sample was observed. A possible association between base-stacking interaction and torsional rigidity was inferred from the comparison of the two samples.     

DNA methylation in vegetative and conjugating cells of a protozoan ciliate: Blepharisma japonicum

We report here the presence of N⁶-methyladenine (MeAde) in the macronuclear DNA (maDNA) of Blepharisma japonicum vegetative cells. We have further investigated the relationship between DNA methylation and cell union in cells activated for conjugation. Such activation was induced by treating cells of mating type I with complementary gamone 2. We found a reduction of about 24% of MeAde content in gamone-treated cells ready for cell union. First indications of the presence and reduction of MeAde content came from electrophoresis of maDNA digested by appropriate restriction endonucleases. Chromatographic determination of the amount of methylated base by HPLC substantiated these observations. In vegetative cells, 1.576 ± 0.02% of total adenine was found to be methylated as opposed to 1.193 ± 0.04% in activated cells. The HPLC analysis of maDNA also revealed a peak with a retention time corresponding to that of 5-hydroxymethyluracil, already found in some species of dinoflagellates. In that gamone treatment is correlated with a differential gene expression (indicated by a differential RNA and protein synthesis), our results suggest that there is a relationship between macronuclear genome activation and demethylation of maDNA. This is the first report of a correlation between gene activation and adenine demethylation in a eukaryotic organism.     

Partial purification of a high molecular weight hepatocyte growth stimulating factor from normal calf serum.

A heparin-binding protein, acting as a potent hepatocyte growth stimulating factor (HGSF) was extracted and partially purified from normal calf serum. HGSF stimulated DNA synthesis and proliferation in primary cultures of adult Balb/c mouse hepatocytes and in two liver-derived epithelial cell lines (C6 and C2.8) plated at low cell density in serum-free medium in the absence of epidermal growth factor. HGSF was non-dialyzable in M(r) 50,000 cutoff membranes, and was purified after chromatofocusing on PBE94 resin, (NH4)2SO4 precipitation (80% salt concentration) of the active fractions eluted at pH 5.7, flow chromatography and elution through Sephacryl S300 HR and HA-Ultrogel columns. The hepatotrophic activity was eluted with a protein fraction that was concentrated approximately 40,000 fold over the starting material. The effect was half maximal at approximately 50 ng/ml on adult hepatocytes in primary culture, HGSF had a molecular weight of 90,000-110,000 by gel filtration, was unstable on heat-treatment and was completely inhibited after trypsin digestion and after reduction with dithiothreitol. HGSF did not stimulate growth in Balb/c 3T3 fibroblasts. When injected into partially (40%) hepatectomized Balb/c mice, HGSF increased hepatic DNA synthesis 2 to 4-fold over the background stimulation, at 20 hours after the hepatectomy.     

Nonlinear methods in spectral analysis of NMR signals from living systems

Two autoregressive procedures, namely Burg's maximum entropy method and Prony's method, have been applied to the processing of 31P NMR signals (free induction decays) of human cells. A comparison of the main advantages obtained by using these methods in the field of the NMR spectral analysis of signals from living samples is here illustrated. Improvements in sensitivity and resolution are obtained with respect to Fourier transform method by using only very few data points.