Structural evidence for gene duplication in the evolution of the acid proteases.

X-ray studies of acid proteases indicate a bilobal structure with a well defined active site cleft. An intramolecular twofold symmetry axis relates two topologically similar domains and the active site residues. A possible mechanism for evolution by gene duplication, divergence and gene fusion is presented.     

Mapping Critical Loads of Acid Deposition for Soils in China

IntroductionThe critical load concept,which is the highestdeposition of acidifying compounds that will notcause long term harmful effectto the ecosystem[1] ,provides a widely used receptor- based approach toallow a more rational abatementstrategy for sulfurdioxide and nitrogen oxides.Many countries haveadopted it as a guideline to formulate thesestrategies. In June,1 994,the Second SulphurProtocol was signed by 2 8countries[2 ] . It wasdecided to reduce the excess sulphur depositionover crit…     

Two Earth-sized planets orbiting Kepler-20

Since the discovery of the first extrasolar giant planets around Sun-like stars, evolving observational capabilities have brought us closer to the detection of true Earth analogues. The size of an exoplanet can be determined when it periodically passes in front of (transits) its parent star, causing a decrease in starlight proportional to its radius. The smallest exoplanet hitherto discovered has a radius 1.42 times that of the Earth's radius (R(⊕)), and hence has 2.9 times its volume. Here we report the discovery of two planets, one Earth-sized (1.03R(⊕)) and the other smaller than the Earth (0.87R(⊕)), orbiting the star Kepler-20, which is already known to host three other, larger, transiting planets. The gravitational pull of the new planets on the parent star is too small to measure with current instrumentation. We apply a statistical method to show that the likelihood of the planetary interpretation of the transit signals is more than three orders of magnitude larger than that of the alternative hypothesis that the signals result from an eclipsing binary star. Theoretical considerations imply that these planets are rocky, with a composition of iron and silicate. The outer planet could have developed a thick water vapour atmosphere.     

Dilute (d) coat colour mutation of DBA/2J mice is associated with the site of integration of an ecotropic MuLV genome

The single endogenous DBA/2J ectropic provirus segregated concordantly with the dilute (d) coat colour mutation on chromosome 9 in 53/53 DBA/2J-derived recombinant inbred mouse strains and all seven inbred and mutant strains tested that carry the d allele. Analysis of DNA from a spontaneous DBA/2J d revertant (d+2J) showed that these mice lack ecotropic-specific MuLV DNA sequences and suggested that the dilute mutation resulted from integration of an ecotropic provirus into the mouse genome.     

Loss of alleles at loci on human chromosome 11 during genesis of Wilms' tumour

Evidence that recessive cellular alleles at specific chromosomal loci are involved in tumorigenesis has been recently shown by work on tissues from patients with retinoblastoma, a neoplasm of embryonic retina whose predisposition is inherited as an autosomal dominant trait. A comparison of germ-line and tumour genotypes at loci on human chromosome 13, defined by restriction fragment length polymorphisms, showed that loss of the chromosome bearing the wild-type allele at the Rb-1 locus occurred frequently in the development of retinoblastoma. We report here results of similar studies of another embryonal neoplasm, Wilms' tumour of the kidney. Examination of germ-line and tumour genotypes from seven patients showed that five cases were consistent with the presence on human chromosome 11 of a locus in which recessive mutational events are expressed after abnormal chromosomal segregation events during mitosis.     

Deletion of steroid 5 alpha-reductase 2 gene in male pseudohermaphroditism

The conversion of testosterone into dihydrotestosterone by steroid 5 alpha-reductase is a key reaction in androgen action, and is essential both for the formation of the male phenotype during embryogenesis and for androgen-mediated growth of tissues such as the prostate. Single gene defects that impair this conversion lead to pseudohermaphroditism in which 46X,Y males have male internal urogenital tracts, but female external genitalia. We have described the isolation of a human 5 alpha-reductase complementary DNA from prostate. Subsequent cloning and genetic studies showed that this gene (designated 5 alpha-reductase 1) was normal in patients with 5 alpha-reductase deficiency. We report here the isolation of a second 5 alpha-reductase cDNA by expression cloning and the polymerase chain reaction. The biochemical and pharmacological properties of this cDNA-encoded enzyme (designated 5 alpha-reductase 2) are consistent with it being the major isozyme in genital tissue. A deletion in this gene is present in two related individuals with male pseudohermaphroditism caused by 5 alpha-reductase deficiency. These results verify the existence of at least two 5 alpha-reductases in man and provide insight into a fundamental hormone-mediated event in male sexual differentiation.     

Simulations of the formation, evolution and clustering of galaxies and quasars

The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a simulation of the growth of dark matter structure using 2,160(3) particles, following them from redshift z = 127 to the present in a cube-shaped region 2.230 billion lightyears on a side. In postprocessing, we also follow the formation and evolution of the galaxies and quasars. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies.