The DNA sequence and biology of human chromosome 19

Chromosome 19 has the highest gene density of all human chromosomes, more than double the genome-wide average. The large clustered gene families, corresponding high G + C content, CpG islands and density of repetitive DNA indicate a chromosome rich in biological and evolutionary significance. Here we describe 55.8 million base pairs of highly accurate finished sequence representing 99.9% of the euchromatin portion of the chromosome. Manual curation of gene loci reveals 1,461 protein-coding genes and 321 pseudogenes. Among these are genes directly implicated in mendelian disorders, including familial hypercholesterolaemia and insulin-resistant diabetes. Nearly one-quarter of these genes belong to tandemly arranged families, encompassing more than 25% of the chromosome. Comparative analyses show a fascinating picture of conservation and divergence, revealing large blocks of gene orthology with rodents, scattered regions with more recent gene family expansions and deletions, and segments of coding and non-coding conservation with the distant fish species Takifugu.     

Community structure and metabolism through reconstruction of microbial genomes from the environment

Microbial communities are vital in the functioning of all ecosystems; however, most microorganisms are uncultivated, and their roles in natural systems are unclear. Here, using random shotgun sequencing of DNA from a natural acidophilic biofilm, we report reconstruction of near-complete genomes of Leptospirillum group II and Ferroplasma type II, and partial recovery of three other genomes. This was possible because the biofilm was dominated by a small number of species populations and the frequency of genomic rearrangements and gene insertions or deletions was relatively low. Because each sequence read came from a different individual, we could determine that single-nucleotide polymorphisms are the predominant form of heterogeneity at the strain level. The Leptospirillum group II genome had remarkably few nucleotide polymorphisms, despite the existence of low-abundance variants. The Ferroplasma type II genome seems to be a composite from three ancestral strains that have undergone homologous recombination to form a large population of mosaic genomes. Analysis of the gene complement for each organism revealed the pathways for carbon and nitrogen fixation and energy generation, and provided insights into survival strategies in an extreme environment.     

Mutations in VKORC1 cause warfarin resistance and multiple coagulation factor deficiency type 2

Coumarin derivatives such as warfarin represent the therapy of choice for the long-term treatment and prevention of thromboembolic events. Coumarins target blood coagulation by inhibiting the vitamin K epoxide reductase multiprotein complex (VKOR). This complex recycles vitamin K 2,3-epoxide to vitamin K hydroquinone, a cofactor that is essential for the post-translational gamma-carboxylation of several blood coagulation factors. Despite extensive efforts, the components of the VKOR complex have not been identified. The complex has been proposed to be involved in two heritable human diseases: combined deficiency of vitamin-K-dependent clotting factors type 2 (VKCFD2; Online Mendelian Inheritance in Man (OMIM) 607473), and resistance to coumarin-type anticoagulant drugs (warfarin resistance, WR; OMIM 122700). Here we identify, by using linkage information from three species, the gene vitamin K epoxide reductase complex subunit 1 (VKORC1), which encodes a small transmembrane protein of the endoplasmic reticulum. VKORC1 contains missense mutations in both human disorders and in a warfarin-resistant rat strain. Overexpression of wild-type VKORC1, but not VKORC1 carrying the VKCFD2 mutation, leads to a marked increase in VKOR activity, which is sensitive to warfarin inhibition.     

Stage-structured cycles promote genetic diversity in a predator-prey system of Daphnia and algae

Competition theory predicts that population fluctuations can promote genetic diversity when combined with density-dependent selection. However, this stabilizing mechanism has rarely been tested, and was recently rejected as an explanation for maintaining diversity in natural populations of the freshwater herbivore Daphnia pulex. The primary limitation of competition theory is its failure to account for the alternative types of population cycles that are caused by size- or stage-dependent population vital rates--even though such structure both explains the fluctuating dynamics of many species and may alter the outcome of competition. Here we provide the first experimental test of whether alternative types of cycles affect natural selection in predator-prey systems. Using competing Daphnia genotypes, we show that internally generated, stage-structured cycles substantially reduce the magnitude of selection (thereby contributing to the maintenance of genetic diversity), whereas externally forced cycles show rapid competitive exclusion. The change in selection is ecologically significant, spanning the observed range in natural populations. We argue that structured cycles reduce selection through a combination of stalled juvenile development and stage-specific mortality. This potentially general fitness-equalizing mechanism may reduce the need for strong stabilizing mechanisms to explain the maintenance of genetic diversity in natural systems.     

Atomic model of a myosin filament in the relaxed state

Contraction of muscle involves the cyclic interaction of myosin heads on the thick filaments with actin subunits in the thin filaments. Muscles relax when this interaction is blocked by molecular switches on either or both filaments. Insight into the relaxed (switched OFF) structure of myosin has come from electron microscopic studies of smooth muscle myosin molecules, which are regulated by phosphorylation. These studies suggest that the OFF state is achieved by an asymmetric, intramolecular interaction between the actin-binding region of one head and the converter region of the other, switching both heads off. Although this is a plausible model for relaxation based on isolated myosin molecules, it does not reveal whether this structure is present in native myosin filaments. Here we analyse the structure of a phosphorylation-regulated striated muscle thick filament using cryo-electron microscopy. Three-dimensional reconstruction and atomic fitting studies suggest that the 'interacting-head' structure is also present in the filament, and that it may underlie the relaxed state of thick filaments in both smooth and myosin-regulated striated muscles over a wide range of species.     

Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1)

Congenital fibrosis of the extraocular muscles type 1 (CFEOM1; OMIM #135700) is an autosomal dominant strabismus disorder associated with defects of the oculomotor nerve. We show that individuals with CFEOM1 harbor heterozygous missense mutations in a kinesin motor protein encoded by KIF21A. We identified six different mutations in 44 of 45 probands. The primary mutational hotspots are in the stalk domain, highlighting an important new role for KIF21A and its stalk in the formation of the oculomotor axis.     

A very energetic supernova associated with the gamma-ray burst of 29 March 2003

Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.     

二烯丙基双酚S醚的合成与表征

以相转移催化法合成了单体二烯丙基双酚Ｓ醚（ＤＡＢＳＥ），采用ＦＴＩＲ，１Ｈ－ＮＭＲ对单体结构进行了验证。ＤＳＣ结果表明：ＤＡＢＳＥ的熔点为１３３℃，热聚合温度高达２８０℃，并具有较宽的聚合峰。