Cyclic AMP stabilizes a class of developmentally regulated Dictyostelium discoideum mRNAs

The stability of mRNA is an important facet of the regulation of protein synthesis. In mammalian cells most mRNAs have long half-lives (5-15 hours) but a substantial fraction are much less stable. There are few examples where the stability of a particular mRNA or class of mRNAs is specifically affected by environmental or developmental stimuli. Certain hormones cause specific stabilization of mRNAs species and preferential mRNA stability is important in the accumulation of globin and myosin mRNAs during the terminal stages of erythropoesis or myogenesis, respectively. Disaggregation of Dictyostelium discoideum aggregates induces the specific destabilization of a large class of developmentally regulated mRNAs; thus, this system is an excellent one in which to determine how such controls are effected. Here we show that addition of cyclic AMP to disaggregated cells specifically prevents the destabilization of these mRNAs.     

Primary structure and functional expression of a developmentally regulated skeletal muscle chloride channel.

Skeletal muscle is unusual in that 70-85% of resting membrane conductance is carried by chloride ions. This conductance is essential for membrane-potential stability, as its block by 9-anthracene-carboxylic acid and other drugs causes myotonia. Fish electric organs are developmentally derived from skeletal muscle, suggesting that mammalian muscle may express a homologue of the Torpedo mamorata electroplax chloride channel. We have now cloned the complementary DNA encoding a rat skeletal muscle chloride channel by homology screening to the Cl- channel from Torpedo. It encodes a 994-amino-acid protein which is about 54% identical to the Torpedo channel and is predominantly expressed in skeletal muscle. Messenger RNA amounts in that tissue increase steeply in the first 3-4 weeks after birth, in parallel with the increase in muscle Cl- conductance. Expression from cRNA in Xenopus oocytes leads to 9-anthracene-carboxylic acid-sensitive currents with time and voltage dependence typical for macroscopic muscle Cl- conductance. This and the functional destruction of this channel in mouse myotonia suggests that we have cloned the major skeletal muscle chloride channel.     

Functional replacement of a protein-induced bend in a DNA recombination site

In recent years the capacity of proteins to bend DNA by binding to specific sites has become a widely appreciated phenomenon. In many cases, the protein-DNA interaction is known to be functionally significant because destruction of the DNA site or the protein itself results in an altered phenotype. An important question to be answered in these cases is whether bending of DNA is important per se or is merely a consequence of the way a particular protein binds to DNA. Here we report direct evidence from the bacteriophage lambda integration system that a bend introduced by a protein is intrinsically important. We find that a binding site for a specific recombination protein known to bend DNA can be successfully replaced by two other modules that also bend DNA; related modules that fail to bend DNA are ineffective.     

Detecting putative recombination events of hepatitis B virus: An updated comparative genome analysis

An updated collection of 791 human hepatitis B virus (HBV) genomes and 38 non-human primate HBV genomes was analyzed for identifying putative recombination events and their recombinants by using two bioinformatics software tools: Simplot and RDP3 with five algorithms (RDP, GENECONV, MaxChi, Chimaera, and SiScan). A total of 61 recombinants from nine putative recombination events were detected with RDP3, especially the breakpoints of six events which have both two parental sequences that can be determined precisely with Simplot. To our knowledge, 53 recombinants were found for the first time. Our study also suggests that a relatively high recombination frequency occurs in the PreC/C gene region and the position near gene boundaries.     

Mammalian chiasma frequencies as a test of two theories of recombination

A broad survey of asexuality in the animal kingdom is sufficient to reject all theories of sex and recombination except two: the Red Queen and the Tangled Bank. The Red Queen theory states that an organism's biotic environment tends to be 'contrary', consistently evolving to the detriment of the organism; sex and recombination result in progeny genetically distinct from their parents and grandparents and thus less susceptible to the antagonistic advances made during the previous generations, particularly by their parasites. The alternative theory, the Tangled Bank, states that sex and recombination function to diversify the progeny from each other, thus reducing competition between them. An extensive survey of mammalian recombination shows that the total number of chiasmata in excess of one per bivalent is strongly correlated with generation time but uncorrelated with fecundity. We conclude that crossing-over may function to combat antagonists with short generation times but does not function to reduce sib competition. Chromosome number is selectively neutral with respect to these factors.     

Computational comparison of two draft sequences of the human genome

We are in the enviable position of having two distinct drafts of the human genome sequence. Although gaps, errors, redundancy and incomplete annotation mean that individually each falls short of the ideal, many of these problems can be assessed by comparison. Here we present some comparative analyses of these drafts. We look at a number of features of the sequences, including sequence gaps, continuity, consistency between the two sequences and patterns of DNA-binding protein motifs.     

Complete mitochondrial genome sequences of two extinct moas clarify ratite evolution

The origin of the ratites, large flightless birds from the Southern Hemisphere, along with their flighted sister taxa, the South American tinamous, is central to understanding the role of plate tectonics in the distributions of modern birds and mammals. Defining the dates of ratite divergences is also critical for determining the age of modern avian orders. To resolve the ratite phylogeny and provide biogeographical data to examine these issues, we have here determined the first complete mitochondrial genome sequences of any extinct taxa--two New Zealand moa genera--along with a 1,000-base-pair sequence from an extinct Madagascan elephant-bird. For comparative data, we also generated 12 kilobases of contiguous sequence from the kiwi, cassowary, emu and two tinamou genera. This large dataset allows statistically precise estimates of molecular divergence dates and these support a Late Cretaceous vicariant speciation of ratite taxa, followed by the subsequent dispersal of the kiwi to New Zealand. This first molecular view of the break-up of Gondwana provides a new temporal framework for speciation events within other Gondwanan biota and can be used to evaluate competing biogeographical hypotheses.     

基于流式细胞技术的两种槭属植物基因组大小测定

【目的】槭属植物具有重要的园林观赏价值和药用价值,开发应用前景广阔,但该属植物分子生物学及基因组学研究还相对匮乏,此次研究利用流式细胞仪技术对该属中鸡爪槭和元宝枫基因组大小进行测定,为后期槭属植物的细胞遗传学和基因组学研究奠定基础。【方法】以鸡爪槭(Acer palmatum)和元宝枫(A. truncatum)的嫩叶为材料,首次采用LB01解离液和碘化丙啶(PI)荧光染料,利用基因组大小已知的玉米(Zea mays L.)CE-777作为内标,建立适合于该两种材料的流式细胞术基因组大小测定方法。【结果】LB01解离液对测定样品与内标解离效果均较好,粒子清晰集中,无重叠峰且区分度良好,最后测得鸡爪槭的基因组1C含量为0.840 4 pg,元宝枫的基因组1C含量为0.756 0 pg。【结论】基于流式细胞仪技术,选取合适的样品处理方法,可成功测定鸡爪槭和元宝枫的基因组大小。该结果和方法可丰富槭属植物的基因库,为揭示该属植物的物种起源和进化提供重要依据,也为其后期的基因组测序工作奠定了重要基础。     

Different substrate-dependent transition states in the active site of the ribosome

The active site of the ribosome, the peptidyl transferase centre, catalyses two reactions, namely, peptide bond formation between peptidyl-tRNA and aminoacyl-tRNA as well as the release-factor-dependent hydrolysis of peptidyl-tRNA. Unlike peptide bond formation, peptide release is strongly impaired by mutations of nucleotides within the active site, in particular by base exchanges at position A2602 (refs 1, 2). The 2'-OH group of A76 of the peptidyl-tRNA substrate seems to have a key role in peptide release. According to computational analysis, the 2'-OH may take part in a concerted 'proton shuttle' by which the leaving group is protonated, in analogy to similar current models of peptide bond formation. Here we report kinetic solvent isotope effects and proton inventories (reaction rates measured in buffers with increasing content of deuterated water, D(2)O) of the two reactions catalysed by the active site of the Escherichia coli ribosome. The transition state of the release factor 2 (RF2)-dependent hydrolysis reaction is characterized by the rate-limiting formation of a single strong hydrogen bond. This finding argues against a concerted proton shuttle in the transition state of the hydrolysis reaction. In comparison, the proton inventory for peptide bond formation indicates the rate-limiting formation of three hydrogen bonds with about equal contributions, consistent with a concerted eight-membered proton shuttle in the transition state. Thus, the ribosome supports different rate-limiting transition states for the two reactions that take place in the peptidyl transferase centre.     

两穴位心电统计学特异性的发现和穴位点定位

在孔最穴和尺泽穴上设计了一个心电信号采集实验,发现了两穴位在心电信号上具有统计学特异性：两穴位上采集的心电信号的二阶统计量与其四周4个非穴位点处采集的心电信号的二阶统计量具有明显区别,且穴位点处心电信号的二阶统计量要明显高于紧挨其周围的4个非穴位点,并用小样本t检验,对所得结论的可信度进行了评价,结果表明：该结论确实具有较高的可信度．这一特性的发现为穴位点定位提供了一个可供选择的方法．     

Different postsynaptic events in two types of retinal bipolar cell

The first synapse in the vertebrate visual system is made between the photoreceptors and the biopolar cells. Bioplar cells fall into two distinct classes according to whether the cell hyperpolarizes or depolarizes to small centred spots of light. Most evidence indicates that the light-induced hyperpolarization of the photoreceptprs suppresses transmitter release from the synaptic terminals, and it is probable that the differences between the two bipolar cell classes results from the different actions of the photoreceptor transmitter. In analysing the membrane potential fluctuations in both types of bipolar cell we find that the voltage noise spectra differ. It is to be expected that postsynaptic noise would be composed of the sum of noise generated in and transmitted from the cones and the noise arising from the statistical nature of synaptic transmission. We report here evidence for two such components in the voltage noise spectra recorded from each type of bipolar cell. The differences in the frequency distribution of the presumed transmitter-related components indicates that the transmitter generates events of longer duration in the depolarizing biopolar cells.     

首例t（8;20）易位的M2—ANLL白血病重组位点的初步研究

对临床上确认为Ｍ２－ＡＮＬＬ的病例，首先进行骨髓细胞染色体的核型分析，经Ｇ显带和Ｒ显色确定为ｔ（８；２０）（ｑ２２；ｐ２３）易位，是一种新的变异型，为进行分子生物学研究，分别设计引物，反转录扩增检测ＥＴＯ基因ｃＤＮＡ ３‘０端顺序和ＥＴＯ融合转录物检测为阴性，从分子水平上排除了经典的ｔ（８，２１）易位的可能性。说明了该病例为ｔ（８；２０）易位，ＥＴＯ基因受累的新变异型白血病。     

Peptide mimetics of an actin-binding site on myosin span two functional domains on actin

The sites on the myosin heavy chain that interact with actin and are responsible for force generation are ill-defined: crosslinking and experiments with isolated domains of the myosin head implicate regions in both the 50K and 20K (molecular weights in thousands) domains of the myosin head (subfragment 1, S1) in this process. We have synthesized peptides from the sequence around the fast-reacting SH1 thiol residue in the 20K domain of S1 in order to delineate precisely an actin-binding site. We used a combination of 1H-NMR and enzyme inhibition assay and also assessed the effects of peptides on skinned rabbit psoas muscle fibres to show that the region of amino acids 690-725 contains an actin-binding site. Peptides from this region bind to actin, act as mixed inhibitors of the actin-stimulated S1 Mg2(+)-ATPase, and influence the contractile force developed in skinned fibres, whereas peptides flanking this sequence are without effect in our test systems. Remarkably, peptides from the N-terminal half of this segment 690-725 increase force development in skinned fibres at submaximal activating concentrations of Ca2+, that is, they behave as calcium-sensitizers; C-terminal peptides, however, inhibit force development without effecting sensitivity to calcium. These different responses indicate that this region is probably binding at two functionally distinct sites on actin.