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At least 127 records · Page 7Linked to original sources
PubMed1985

Conservation of major nuclease S1-sensitive sites in the non-conserved spacer region of ribosomal DNA in Drosophila species.

We have analysed nuclease S1-sensitive sites in cloned ribosomal DNA repeats from Drosophila melanogaster, D. hydei and D. virilis. All species contain major S1-sensitive sites in the spacer near the region of transcription termination, albeit with somewhat different positions and sensitivities. The same sites are also sensitive to the single-strand specificity of Bal31 nuclease at neutral pH. Additional major sites exist at each end of the intervening sequence within the 28 S gene of non-transcribed intervening-sequence-positive ribosomal DNA units of D. hydei. Only minor sites, however, were detected in the Pol I promoter regions. This is in contrast to Pol II transcribed genes, where S1 hypersensitivity becomes apparent at the 5' ends during gene expression. We have sequenced and mapped the S1 sites in the D. hydei spacer. They consist mainly of alternating A and T nucleotides that could form small cruciform structures. Cross-hybridization at low stringencies between the relevant S1-sensitive spacer regions of the three species indicates that the sites lie within very divergent sequences. We discuss the potential functional significance of S1 sites in rDNA spacers and intervening sequences, and the manner in which they might be maintained during rDNA sequence divergence.

Animals↗
PubMed1996

The hypercube structure of the genetic code explains conservative and non-conservative aminoacid substitutions in vivo and in vitro.

A representation of the genetic code as a six-dimensional Boolean hypercube is described. This structure is the result of the hierarchical order of the interaction energies of the bases in codon-anticodon recognition. In this paper it is applied to study molecular evolution in vivo and in vitro. In the first case we compared aligned positions in homologous protein sequences and found two different behaviors: (a) There are sites in which the different amino acids may be explained by one or two 'attractor nodes' (coding for the dominating amino acid(s)) and their one-bit neighbors in the codon hypercube; and (b) There are sites in which the amino acids correspond to codons located in closed paths in the hypercube. In the second case we studied the 'Sexual PCR'1 experiment described by Stemmer [Stemmer (1994)] and found that the success of this combination of usual PCR and recombination is in part due to the Gray code structure of the genetic code.

Amino Acids↗
PubMed1987

[Nutrient dependence of energy conservation requirements in rats. 4. The influence of protein levels of food on energy conservation requirements of rats during growth and after conclusion of the intensive growth phase].

Albino rats bred in the institute (Wistar line) divided into 3 groups of 9 animals each received, beginning at the age of 4 weeks, feed mixtures with 10, 40 and 70% protein in the rations over a period of 24 weeks divided into 14 subperiods of study. The feed mixture changed cyclically for the groups of animals after each sub-period. Every period was divided into a growth period (8 days) with the rats kept in metabolism cages and a period of feeding on maintenance level (4 days) with the rats kept in respiration chambers. In both periods the temperature was kept constant at 30 degrees C. On 3 days of feeding on the maintenance level the metabolism parameters of energy, C and N metabolism were measured and energy maintenance requirement was ascertained. Both the energy maintenance requirement of the growing rats (up to 200 g live weight) and that of the nearly fully grown and fully grown rats resp. (greater than 200 g live weight) significantly depended on the nutrient composition of the feed mixtures supplied. It increased with the increasing protein and simultaneously decreasing carbohydrate quotas in the feed. On an average of the studies the rats had, in the sequence of 10, 40 and 70% protein content, an energy maintenance requirement of 383 +/- 31 (n = 105), 415 +/- 31 (n = 106) and 459 +/- 36 kJ metabolizable energy/kg LW0.75.d (n = 102). Energy maintenance requirement behaved relatively like 100:108:120. Based on the fact that energy maintenance requirement may be considered the requirement of ATP, relative expectancy values for energy maintenance requirement can be calculated with the energetic efficiency of the ATP synthesis (kJ metabolizable energy/Mol ATP gain) in nutrient catabolism from the relation of the experimentally ascertained nutrient metabolism at a variant supply of protein of 100:110:118. The hypothesis that the efficiency of ATP synthesis in the catabolism of the main nutrients supplying energy can be considered a relative measure of the dependence of the energy maintenance requirement on nutrient composition has been confirmed in this experiment. Different findings in earlier experiments raise the question if those findings were influenced by adaptation effects. An experimental solution of this question is considered important.

Adenosine Triphosphate↗