Size variation in chromosomes from independent cultured isolates of Plasmodium falciparum

The complexity of the life cycle of the protozoan malaria parasite Plasmodium falciparum has hindered genetic analysis; even the number of chromosomes in P. falciparum is uncertain. The blood stages of rodent malaria parasites are haploid and hybridization with cloned complementary DNAs similarly suggests a haploid genome in P. falciparum blood stages (ref. 4 and our unpublished results). A novel approach to karyoptic and linkage analysis in P. falciparum has been provided recently by the technique of pulsed-field gradient (PFG) gel electrophoresis, which allows the fractionation of DNA molecules of 30-3,000 kilobases (kb), a range including the sizes of intact chromosomal DNA molecules from eukaryotes such as yeast and trypanosomatids. We describe here the fractionation by PFG electrophoresis of chromosomal DNA molecules from P. falciparum into at least seven discrete species which vary in size by up to 20% between different isolates. Several genes for P. faciparum antigens which contain repetitive sequences are located on different chromosomes. Surprisingly, two of the chromosomes seem to contain the same sequences.     

Astronomical pacing of methane release in the Early Jurassic period

A pronounced negative carbon-isotope (delta13C) excursion of approximately 5-7 per thousand (refs 1-7) indicates the occurrence of a significant perturbation to the global carbon cycle during the Early Jurassic period (early Toarcian age, approximately 183 million years ago). The rapid release of 12C-enriched biogenic methane as a result of continental-shelf methane hydrate dissociation has been put forward as a possible explanation for this observation. Here we report high-resolution organic carbon-isotope data from well-preserved mudrocks in Yorkshire, UK, which demonstrate that the carbon-isotope excursion occurred in three abrupt stages, each showing a shift of -2 per thousand to -3 per thousand. Spectral analysis of these carbon-isotope measurements and of high-resolution carbonate abundance data reveals a regular cyclicity. We interpret these results as providing strong evidence that methane release proceeded in three rapid pulses and that these pulses were controlled by astronomically forced changes in climate, superimposed upon longer-term global warming. We also find that the first two pulses of methane release each coincided with the extinction of a large proportion of marine species.     

Evolution of phosphofructokinase--gene duplication and creation of new effector sites

Phosphofructokinases (PFK; EC 2.7.1.11) are tetrameric enzymes that have a key role in the regulation of glycolysis; as such, they are subject to allosteric activation and inhibition by various metabolites. Eukaryotic PFKs are about twice the size of prokaryotic enzymes and are regulated by a wider repertoire of effectors: for example, the subunit molecular weights of rabbit muscle (RM) PFK and Bacillus stearothermophilus (Bs) PFK are 82,000 and 36,000, respectively. Both enzymes are activated by ADP (or AMP), but RM-PFK is also activated by fructose bisphosphates (FBP) and inhibited by ATP and citrate. This, together with other evidence, has led to speculation that mammalian PFKs have evolved by duplication of a prokaryotic gene, although previous peptide analysis failed to reveal internal homology in RM-PFK. Here we demonstrate clear homology among the N- and C-halves of RM-PFK and Bs-PFK, thus establishing an evolutionary relationship by series gene duplication and divergence. Furthermore, detailed knowledge of the Bs-PFK structure provides the basis for inferences concerning the structural organization of RM-PFK and the evolution of new effector sites in the enzyme tetramer.     

虚拟空间和吸引子

当我们能够在从三维空间表面上去观察吸引子时，我们会比较容易地理解数学的过程。尽管我们还不能真正视察到这些吸引子存在的所有维数，它们仍然会使我们一饱眼福。我们中间有些人能自如地把握住（或仅仅只能适当地把握住）数学程序被想象为空间过程的时刻，对于他们，混沌系统的图像绘制方法是作为一种令人欣慰的某些东西而出现的，它开拓了自笛卡儿时代以来对符号运算的逻辑学家已经失去的视觉颌地。混浊的代数用图像的方式在计算机屏幕背后的虚拟空间里结出了丰硕成果，共产生出为电子调色板的新艺术品鉴赏家所惊讶的混饨吸引子和分形自…     

Do taste receptors respond to perturbation of water structure?

The pmr spin-spin pulse relaxation times (T2 values) of the L-amino acids are examined in relation to their taste threshold values. There is an inverse trend between T2 value and threshold value with a good correlation for amino acids whose natural pH is close to neutrality. These results may indicate that taste receptors respond to perturbation of water structure.