Structural basis of DNA replication origin recognition by an ORC protein

DNA replication in archaea and in eukaryotes share many similarities. We report the structure of an archaeal origin recognition complex protein, ORC1, bound to an origin recognition box, a DNA sequence that is found in multiple copies at replication origins. DNA binding is mediated principally by a C-terminal winged helix domain that inserts deeply into the major and minor grooves, widening them both. However, additional DNA contacts are made with the N-terminal AAA+ domain, which inserts into the minor groove at a characteristic G-rich sequence, inducing a 35 degrees bend in the duplex and providing directionality to the binding site. Both contact regions also induce substantial unwinding of the DNA. The structure provides insight into the initial step in assembly of a replication origin and recruitment of minichromosome maintenance (MCM) helicase to that origin.     

A role for interaction of the RNA polymerase flap domain with the sigma subunit in promoter recognition

In bacteria, promoter recognition depends on the RNA polymerase sigma subunit, which combines with the catalytically proficient RNA polymerase core to form the holoenzyme. The major class of bacterial promoters is defined by two conserved elements (the -10 and -35 elements, which are 10 and 35 nucleotides upstream of the initiation point, respectively) that are contacted by sigma in the holoenzyme. We show that recognition of promoters of this class depends on the "flexible flap" domain of the RNA polymerase beta subunit. The flap interacts with conserved region 4 of sigma and triggers a conformational change that moves region 4 into the correct position for interaction with the -35 element. Because the flexible flap is evolutionarily conserved, this domain may facilitate promoter recognition by specificity factors in eukaryotes as well.     

A calcium-dependent protein kinase with a regulatory domain similar to calmodulin.

Calcium can function as a second messenger through stimulation of calcium-dependent protein kinases. A protein kinase that requires calcium but not calmodulin or phospholipids for activity has been purified from soybean. The kinase itself binds calcium with high affinity. A complementary DNA clone for this kinase has been identified; it encodes a protein with a predicted molecular mass of 57,175 daltons. This protein contains a catalytic domain similar to that of calmodulin-dependent kinases and a calmodulin-like region with four calcium binding domains (EF hands). The predicted structure of this kinase explains its direct regulation via calcium binding and establishes it as a prototype for a new family of calcium-regulated protein kinases.     

Lunar eclipse: infrared images and an anomaly of possible internal origin

Infrared images of the lunar eclipse of 13 April 1968 were obtained and compared with infrared images of the 19 December 1964 eclipse. A similarity of apparent strength and distribution of most thermal anomalies on the maria is evident from inspection of these images, indicating that these features are not ephemeral. One new linear thermal anomaly was discovered, which is thermally enhanced during the lunar afternoon. Its close relation to a lunar crustal fracture line and other features of probable internal origin suggests that this anomaly may be of internal origin.     

On the origin of internal structure of word forms

This study shows that a corpus of proto-word forms shares four sequential sound patterns with words of modern languages and the first words of infants. Three of the patterns involve intrasyllabic consonant-vowel (CV) co-occurrence: labial (lip) consonants with central vowels, coronal (tongue front) consonants with front vowels, and dorsal (tongue back) consonants with back vowels. The fourth pattern is an intersyllabic preference for initiating words with a labial consonant-vowel-coronal consonant sequence (LC). The CV effects may be primarily biomechanically motivated. The LC effect may be self-organizational, with multivariate causality. The findings support the hypothesis that these four patterns were basic to the origin of words.     

Insect photoreceptor: an internal ocellus is present in sphinx moths

Adult sphinx moths lack external ocelli. In Manduca sexta and other anocellate moths structures homologous to ocelli have been observed. Histological examination of such a structure in Manduca sexta has shown structural similarities to ocelli of other insects. Electrophysiological studies revealed a response to light stimuli stimilar to the electroretinogram of external ocelli. The evidence strongly suggests that the structures are internal ocelli.     

花青素合成调节基因Rosea1转化东方百合索邦的研究

以东方百合索邦无菌苗鳞片为受体材料,利用农杆菌介导法将花秦素合成调节基因Rosea1导入百合,并对遗传转化体系进行优化。结果表明,外植体经过1 d预培养、侵染液以及共培养基中均加入50μmol/L乙酰丁香酮(AS)、共培养基去除NH4NO3并将pH值调至5.5,共培养3 d,有利于提高遗传转化率。获得的部分抗性植株经PCR检测,扩增出特异条带,初步证明Rosea1基因已整合到索邦百合基因组DNA中。     

Petrogenesis of lunar basalts and the internal constitution and origin of the moon

Petrographic and electron-microprobe studies combined with high pressure-temperature investigations of phase relationships in average Apollo 11 basalt and possible source material show that the lower parts of maria may be composed of eclogite (density 3.74 grams per cubic centimeter), thus explaining the existence of mascons. The Apollo 11 basalt was probably formed at depths of 200 to 400 kilometers by a small degree of partial melting from pyroxenitic source material [FeO/(FeO + MgO) = 0.25, A1(2)O(3) 4 percent, CaO 3 percent]. This composition may be representative of the lunar interior and yields the observed mean lunar density and moment of inertia. Present data are in conflict with fission, binary planet, and capture hypotheses of lunar origin but are consistent with Ringwood's (1966) precipitation hypothesis.     

Unwinding of duplex DNA from the SV40 origin of replication by T antigen

The T antigen specified by SV40 virus is the only viral-encoded protein required for replication of SV40 DNA. T antigen has two activities that appear to be essential for viral DNA replication: specific binding to duplex DNA at the origin of replication and helicase activity that unwinds the two DNA strands. As judged by electron microscopy, DNA unwinding is initiated at the origin of replication and proceeds bidirectionally. Either linear or circular DNA molecules containing the origin of replication are effective substrates; with closed circular DNA, a topoisomerase capable of removing positive superhelical turns is required for an efficient reaction. Presence of an origin sequence on duplex DNA and a single-strand DNA-binding protein appear to be the only requirements for T antigen to catalyze unwinding. This reaction mediated by T antigen defines a likely pathway to precise initiation of DNA replication: (i) the sequence-specific binding activity locates the origin sequence, (ii) the duplex DNA is unwound at this site, and (iii) the DNA polymerase and primase begin DNA replication. A similar pathway has been inferred for the localized initiation of DNA replication by bacteriophage lambda and by Escherichia coli in which a sequence-specific binding protein locates the origin and directs the DnaB helicase to this site. Observations with the SV40 system indicate that localized initiation of duplex DNA replication may be similar for prokaryotes and eukaryotes.     

Structures of glycoprotein Ibalpha and its complex with von Willebrand factor A1 domain

Transient interactions of platelet-receptor glycoprotein Ibalpha (GpIbalpha) and the plasma protein von Willebrand factor (VWF) reduce platelet velocity at sites of vascular damage and play a role in haemostasis and thrombosis. Here we present structures of the GpIbalpha amino-terminal domain and its complex with the VWF domain A1. In the complex, GpIbalpha wraps around one side of A1, providing two contact areas bridged by an area of solvated charge interaction. The structures explain the effects of gain-of-function mutations related to bleeding disorders and provide a model for shear-induced activation. These detailed insights into the initial interactions in platelet adhesion are relevant to the development of antithrombotic drugs.     

V1 neurons signal acquisition of an internal representation of stimulus location

A fundamental aspect of visuomotor behavior is deciding where to look or move next. Under certain conditions, the brain constructs an internal representation of stimulus location on the basis of previous knowledge and uses it to move the eyes or to make other movements. Neuronal responses in primary visual cortex were modulated when such an internal representation was acquired: Responses to a stimulus were affected progressively by sequential presentation of the stimulus at one location but not when the location was varied randomly. Responses of individual neurons were spatially tuned for gaze direction and tracked the Bayesian probability of stimulus appearance. We propose that the representation arises in a distributed cortical network and is associated with systematic changes in response selectivity and dynamics at the earliest stages of cortical visual processing.     

水稻OsGRAS1启动子的克隆及多样性分析

通过克隆水稻抗旱QTL区段内抗旱相关基因OsGRAS1上游1 332 bp的调控元件启动子序列,并对其进行顺式作用元件分析发现:该序列具有典型的真核生物核心启动子结构,并且包含多个与干旱胁迫相关和激素应答的调控元件;根据该序列在93-11和日本晴的同源序列间存在的插入缺失位点设计引物,在120份稻种资源中对OsGRAS1启动子片段进行序列多样性分析发现,存在4种不同类型的启动子序列,其中Ⅳ型OsGRAS1启动子比其他3种类型多了3个顺式作用元件:MYB1LEPR,GTICORE,NTBBF1ARROLB.每种序列类型选取1份材料,进行冷、盐、外源ABA和PEG胁迫处理,分析其下游基因OsGRAS1的表达水平.结果表明:Ⅳ型材料的启动子对ABA和PEG处理较其他3种类型更敏感.     

猪THRSP基因5'调控区多位点SNP联合效率的研究

旨在分析猪THRSP基因5’调控区多位点SNP联合调控THRSP基因表达的效率。实验从猪基因组获取包含多位点SNP的目的片段,利用荧光素酶报告基因pGL3-Basic构建表达载体,检测多位点SNP 的联合启动效率,并通过实时荧光定量PCR进行THRSP基因表达验证分析。结果表明,在5个SNP位点中,TCAGA 的启动效率最高,比CTGGA的启动效率高129％,而CCAGA、CTAGA和CTGAT的启动效率较CTGGA分别低99.0%、73.2％和42.6％。TCAGA的启动效率较CCAGA高75.6％,而CCAGA比CTAGA的启动效率高96.6％;报告基因所揭示的SNP启动效率与THRSP基因实时荧光定量PCR结果一致。     

Requirement of the prolyl isomerase Pin1 for the replication checkpoint

The peptidyl-prolyl isomerase Pin1 has been implicated in regulating cell cycle progression. Pin1 was found to be required for the DNA replication checkpoint in Xenopus laevis. Egg extracts depleted of Pin1 inappropriately transited from the G2 to the M phase of the cell cycle in the presence of the DNA replication inhibitor aphidicolin. This defect in replication checkpoint function was reversed after the addition of recombinant wild-type Pin1, but not an isomerase-inactive mutant, to the depleted extract. Premature mitotic entry in the absence of Pin1 was accompanied by hyperphosphorylation of Cdc25, activation of Cdc2/cyclin B, and generation of epitopes recognized by the mitotic phosphoprotein antibody, MPM-2. Therefore, Pin1 appears to be required for the checkpoint delaying the onset of mitosis in response to incomplete replication.     

牦牛CAPN1基因部分序列的SNPs研究

本研究采用PCR-SSCP技术,设计了2对引物分别对牦牛钙激活蛋白酶基因内含子8、外显子9、内含子9和外显子10部分序列以及第12内含子和13外显子部分序列进行单核苷酸多态性分析.结果表明:与牛基因序列(AF252504S2)相比,牦牛基因在10 581bp处发生了G→A转换,位于第12内含子,表现出3种基因型,其中A、B基因频率分别为0.698 9和0.301 1,AA、AB和BB基因型频率分别为0.475 1、0.447 5和0.077 3,遗传杂合度(He)和多态信息含量(PIC)分别为0.420 9和0.332 3;在5 837bp处发生G→T的转换,位于第9内含子,表现出3种基因型,A、B基因频率分别为0.908 8和0.091 2,AA、AB和BB基因型频率分别为0.828 7、0.160 2和0.011 1,遗传杂合度(He)多态信息含量(PIC)分别为0.165 7和0.152 0;牦牛在这2个位点上处于Hardy-Weinberg平衡状态.