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991.
992.
993.
The synthesis of methyl 3-azido- and 3-amino-2,3-dideoxyhexopyranosiduronic acids and their methyl esters with the -alpha,beta-D-arabino-, -alpha,beta-D-ribo, and -alpha,beta-L-lyxo configurations is presented. The conformations of the synthesized sugar amino acids and their precursors are discussed on the basis of 1H NMR data. The influence of the 5-carboxyl group on the pyranose ring conformation is assessed, and the bonding of the monosugar amino acids into dimeric glycotides, using conventional solution-phase peptide syntheses, is reported. 相似文献
994.
Parthenogenesis and, in particular, polyploidy are rare in animals. A number of cases, known among weevils, represent apomictic parthenogenesis-a reproductive mode in which eggs undergo one maturation division, the chromosomes divide equationally, and no reduction takes place. Among parthenogenetic weevils there are two diploids, 48 triploids, 18 tetraploids, six pentaploids, three hexaploids and one decaploid. Eight examined parthenogenetic species are triploids with 33 chromosomes of different morphology, confirming that triploidy is the most common level of ploidy in weevils. The karyotypes are heterogeneous with the presence of meta-, submeta-, subtelo- and acrocentric chromosomes. The C-banding method showed that only two species possess a large amount of heterochromatin visible as a band around the centromere during mitotic metaphase. This agrees with observations that weevils are characterized by a small amount of heterochromatin, undetectable in metaphase plates after C-banding. In three species an atypical course of apomictic oogenesis occurs with stages similar to meiosis, in which chromosomes form bivalents and multivalent clusters. This association of chromosomes probably represents the remnants of meiosis, although these events have nothing to do with recombination. The results support the hypothesis that the evolution of apomictic parthenogenesis in weevils has proceeded through a stage of automixis. 相似文献
995.
Interactions between stressful environment and gene deletions alleviate the expected average loss of fitness in yeast 下载免费PDF全文
The conjecture that the deleterious effects of mutations are amplified by stress or interaction with one another remains unsatisfactorily tested. It is now possible to reapproach this problem systematically by using genomic collections of mutants and applying stress-inducing conditions with a well-recognized impact on metabolism. We measured the maximum growth rate of single- and double-gene deletion strains of yeast in several stress-inducing treatments, including poor nutrients, elevated temperature, high salinity, and the addition of caffeine. The negative impact of deletions on the maximum growth rate was relatively smaller in stressful than in favorable conditions. In both benign and harsh environments, double-deletion strains grew on average slightly faster than expected from a multiplicative model of interaction between single growth effects, indicating positive epistasis for the rate of growth. This translates to even higher positive epistasis for fitness defined as the number of progeny. We conclude that the negative impact of metabolic disturbances, regardless of whether they are of environmental or genetic origin, is absolutely and relatively highest when growth is fastest. The effect of further damages tends to be weaker. This results in an average alleviating effect of interactions between stressful environment and gene deletions and among gene deletions. 相似文献
996.
Analysis of the grass Zingeria trichopoda (2n = 8, 2C = 5.3 pg) revealed a dynamic evolution with the following characteristics. (i) Genomic in situ hybridization (GISH) demonstrates that Z. trichopoda evolved from an interspecific hybrid involving a species like contemporary Zingeria biebersteiniana (2n = 4) and a second species with a similar low number of chromosomes. The nucleus of Z. trichopoda is spatially organized at the genome level and the two parental genomes occupy distinct and separate domains of lateral arrangements. (ii) The copy number of the Z. biebersteiniana specific pericentromeric tandem repeat family Zbcen1 is drastically reduced in Z. trichopoda. (iii) GISH in combination with labeled rDNA sequences simultaneously discriminated the two parental genomes and the corresponding 5S and 45S rDNA sites. Hence, following allopolyploidization of Z. trichopoda the Z. biebersteiniana like parental chromosomes probably underwent drastic loss of 45S rDNA. This could have arisen either through the loss of Z. biebersteiniana derived 45S rDNA or through Z. trichopoda genome-wide homogenization of Z. biebersteiniana type 45S rDNA and subsequent elimination of 45S rDNA loci from Z. biebersteiniana derived chromosomes. Finally, 5S rDNA loci are present in both subgenomes of Z. trichopoda and the chromosomal position of these loci is similar for both Z. biebersteiniana and the Z. biebersteiniana like parental genome of Z. trichopoda. 相似文献
997.
Piotr Przybylski Krystian Pyta Dorota Remlein-Starosta Grzegorz Schroeder Bogumil Brzezinski Franz Bartl 《Bioorganic & medicinal chemistry letters》2009,19(7):1996-2000
Eight alkyl and six heterocyclic aza-derivatives of gossypol (2–15) have been synthesized using gossypol (1) extracted from Gossypium Herbaceum cottonseeds. The ability of gossypol aza-derivatives to form complexes with NaClO4 has been investigated by electrospray ionisation (ESI) mass spectra recorded in the positive and negative ion detection modes. The gossypol aza-derivatives have been characterized by FT-IR, 1H and 13C NMR spectroscopic methods and subsequently tested for their antifungal properties against Fusarium oxysporum. Four alkyl aza-derivatives (2–5), present in the enamine–enamine tautomeric form, have shown activity comparable or higher than that of gossypol against this fungus. To improve the antifungal activity the complexes of the most active compounds 2–5 with NaClO4 were prepared. Complexes of 2 and 5 with NaClO4 have shown antifungal activity higher than that of the uncomplexed compounds. 相似文献
998.
999.
Dorota Latek 《BMC structural biology》2017,17(1):8