Structure of Poly (dT)·Poly (dA)·Poly (dT)

Abstract

The molecular structure of poly (dT)·poly (dA)·poly (dT) has been determined and refined using the continuous x-ray intensity data on layer lines in the diffraction pattern obtained from an oriented fiber of the DNA. The final R-value for the preferred structure is 0.29 significantly lower than that for plausible alternatives. The molecule forms a 12-fold right- handed triple-helix of pitch 38.4 Å and each base triplet is stabilized by a set of four Crick-Watson-Hoogsteen hydrogen bonds. The deoxyribose rings in all the three strands have C2′-endo conformations. The grooveless cylindrical shape of the triple-helix is consistent with the lack of lateral organization in the fiber.     

杂交柑桔的胚胎发育(英文)

柑桔类珠心胚现象对研究其进化和种质保存方面有着重要意义,但是给其有性杂交育种工作造成相当大的麻烦：它不仅使杂交后代难于区分合子苗和珠心苗,而且会使合子胚发育中途天折。解决的途径是适时分离合子胚进行单独培养。为此,本工作于柑桔胚胎发育的不同时期取样、固定、观察,研究其合子胚发育规律,确定珠心胚侵入胚囊的时期。结果表明：一般情况下,授粉后３０ｄ,合于处于单细胞状态（Ｆｉｇ．１Ａ）;授粉后４０ｄ;合子开始分裂（Ｆｉｇ．１Ｂ）;授粉后４５ｄ,合子胚形成８－１６个细胞,珠心胚开始分裂（Ｆｉｇ．１Ｃ）;授粉后５０ｄ,合子形成球形胚,珠心胚尚未侵入胚囊（Ｆｉｇ．１Ｄ＆Ｅ）;授粉后５５ｄ,合子胚为球形胚或早心形胚,开始有少数珠心胚侵入胚囊（Ｆｉｇ．１Ｄ＆Ｅ）;授粉后６０ｄ,合子胚为心形胚（Ｆｉｇ．１Ｇ）。授粉后８０ｄ,合子胚为晚心形,珠心胚巨大量侵入并迅速发育（Ｆｉｇ．１Ｈ）。杂交的组合对合子,胚珠及果实发育均有一定影响,主要取决于杂交亲本。与种间杂交相比,属间杂交其合子分裂较迟,合子胚发育较慢,珠心胚侵入时期也较迟（Ｔａｂｌｅｌ,Ｆｉｇ．２）。这种发育速度的差异,引起所产生的合子胚的大小（Ｔａｂｌｅ２）珠心胚侵率（Ｔａｂ     

Structures for the polynucleotide complexes poly(dA) · poly(dT) and poly(dT) · poly(dA) · poly(dT)

X-ray diffraction analyses of fibers of polydeoxyadenylic acid · polydeoxythymidylic acid show that this molecule exists as a 10-fold double-helix with axial rise per nucleotide $\text{h = 3.24}\text{to}\text{3.29}\text{A}\text{?}$. The structure is very similar to B-DNA ($\text{h = 3.37}\text{A}\text{?}$) in having C3-exo furanose rings and base-pairs positioned centrally on the helix axis, but distinctive enough to have two packing modes, neither of which has been observed for B-DNA. Although the triple-stranded poly(dT) · poly(dA) · poly(dT) also has a large value of h(3.26 Å), each of the chains is a 12-fold helix of the A-genus with C3-endo furanose rings and bases displaced several Angstrom units from the helix axis.     

Studies on synthetic chromatins containing poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC)

Core histones, (H2A,H2B,H3,H4)₂, were reconstituted with the synthethic polynucleotides poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC) to yield synthetic chromatins containing 200 basepairs per octamer. These synthetic chromatins displayed a 36% decrease in the circular dichroism (CD) peak ellipticity from the value of the polynucleotide free in solution; the poly(dA-dT)·poly(dA-dT)/chromatin showed an increase in the complexity of the thermal denaturation profile compared to that of the polynucleotide. Both the temperature of maximum $\text{d}\text{h}\text{d}\text{T}$ for each transition (T_m) and the relative amount of poly(dA-dT)·poly(dA-dT) in the synthetic chromatin melting in each of the four thermal transitions is a function of the ionic strength over the 0–5 mM sodium phosphate range (0.25 mM EDTA, pH 7.0); a shift of material toward higher melting transitions was observed with increasing ionic strength. The CD peak ellipticity value for both synthetic chromatins was ionic strength-independent over the 0–5 mM sodium phosphate range. These results are in contrast to those observed with $\text{H}\text{1}\text{H}\text{5}$ stripped chicken erythrocyte chromatin (Fulmer, A. and Fasman, G.D. (1979) Biopolymers 18, 2875–2891), where an ionic strength dependence was found. Differences in the CD spectra between poly(dA-dT)·poly(dA-dT)/chromatin, poly(dG-dC)·poly(dG-dC)/chromatin and $\text{H}\text{1}\text{H}\text{5}$ stripped chicken erythrocyte chromatin suggest subtle differences in assembly. Finally, the temperature dependence of the CD spectra of poly(dA-dT)·poly(dA-dT)-containing synthetic chromatin, which is similar to that for the polynucleotide, suggests the core histone bound polynucleotide has a large degree of conformational flexibility allowing it to undergo the premelt transition.     

抑制性扣除杂交技术(SSH)及其研究进展

一般认为,真核生物基因总数为100,000个左右。但在一定发育阶段,在某一类型的细胞当中,则只有15%左右的基因得以表达[1]。而生物体几乎所有的生命活动过程包括病理的变化,从本质上讲均是基因表达变化的结果。因此,关于真核生物发育过程中基因的表达与调控的研究已引起人们的高度重视。过去,人们对差异表达基因的分离主要依赖于示差筛选和差别杂交技术,但它们又存在着重复性差、敏感度低等缺点。近几年,随着ＰＣＲ技术的出现,涌现了许多基于ＰＣＲ的分离有差别表达基因的新方法。1992年ＬｉａｎｇＰ等[2]提出ｍＲＮＡ差异显示技术(ｍＲＮＡｄ…     

植物分子生态学进展(Ⅰ)——遗传结构和杂交(英)

从物种遗传结构和杂交的角度介绍了当前植物分子生态学研究的新进展。对于物种遗传结构,文章分析了物种生物学特性、生态因子对它的影响,强调了种群不同世代遗传结构研究的重要性。而在杂交研究领域,文章揭示了分子生物学手段有着比传统形态分析方法更多的优越性。     

The Structure of Triple Helical Poly(U)·Poly(A)·Poly(U) Studied by Raman Spectroscopy

Abstract

Using Raman spectroscopy, we examined the ribose-phosphate backbone conformation, the hydrogen bonding interactions, and the stacking of the bases of the poly(U)·poly(A) ·poly(U) triple helix. We compared the Raman spectra of poly(U)·poly(A)·poly(U) in H₂O and D₂O with those obtained for single-stranded poly(A) and poly(U) and for double-stranded poly(A)·poly(U). The presence of a Raman band at 863 cm^?1 indicated that the backbone conformations of the two poly(U) chains are different in the triple helix. The sugar conformation of the poly(U) chain held to the poly(A) by Watson-Crick base pairing is C3′ endo; that of the second poly(U) chain may be C2′ endo. Raman hypochromism of the bands associated with base vibrations demonstrated that uracil residues stack to the same extent in double helical poly(A)·poly(U) and in the triple-stranded structure. An increase in the Raman hypochromism of the bands associated with adenine bases indicated that the stacking of adenine residues is greater in the triple helix than in the double helical form. Our data further suggest that the environment of the carbonyls of the uracil residues is different for the different strands.     

杂交水稻植株组织的器官发生(简报)

近年来,植物组织培养和细胞培养的研究迅速发展,在生产上的作用也日益明显(罗士韦 1978)。禾谷类植物是重要的粮食作物,其组织与细胞培养及其在生产实际中的应用,一直受人重视。但目前禾谷类植物的组织培养与细胞培养尚不完善,能培养的材料仍然有限(Yamada 1977)。如以水稻为例,虽有不少人曾利用去壳的种子(Nishi等 1968)、胚根(Kawata等 1968)、胚(Maeda 1968,Tamura     

枸杞属(茄科)新类群杂交起源初探

为探讨枸杞属新类群的起源及国产枸杞属植物的亲缘关系,该文使用核基因颗粒性结合淀粉合成酶基因(GBSSI)片段,对国产7个类群的枸杞属植物进行了分子系统学研究.结果表明:中国分布的枸杞属植物属于旧世界类群并分为4个强烈支持的分支,而新类群的形成与杂交密切相关.此外,初步分析还显示宁夏枸杞有较高的遗传分化.     

王莲(Victoria)杂交后代表型观察分析

以克鲁兹王莲ב朗伍德王莲自交后代’的58个后代为材料,观察分析了叶片卷边颜色、花蕾形状、萼片颜色、萼片着刺数、第1晚和第2晚花色等10个主要性状的分离情况,并对个体性状分离类型进行了聚类。结果表明,其后代性状分离极为广泛,主要表现为负向中亲优势、正向中亲优势和超亲优势。第1晚内瓣色、拟雄蕊尖色、第2晚内瓣色、第2晚外瓣色及第2晚内外瓣色差5个性状之间有高度或显著相关性,其余相关性较低;卷边色、蕾形、萼片颜色、着刺数及第1晚外瓣色5个性状独立遗传的可能性大。个体性状分离类型丰富,主要可分为7大类,绿叶粉花白芯型、红叶玫红花白芯型、绿叶玫红花深玫红芯型、红叶玫红花深玫红芯型、绿叶深玫红花白芯型、红叶粉花深玫红芯型、绿叶萼多刺玫红花白芯型。     

植物的体细胞杂交和基因转移研究进展(II)

四、种群间的体细胞杂种对于育种家来说,最期望的是通过原生质体融合,把优良性状转移到那些不亲和性的物种中去.在十字花科植物中,我们已经选择了山芥(Barbarea vulgaris)和穿叶遏蓝菜(Thlaspi perfoliatum)作为融合油菜的亲本.因为山芥属植物具有抗寒性,遏蓝菜属植物含有一种可以用作润滑剂的神经酸.它们与拟南芥芸苔杂种不同,其分离杂种的原生质体愈伤组织容易再生成苗,而在发根和幼苗移栽方面较困难.     

Differential expression of ·1(IV), ·2(IV), ·5(IV) and ·6(IV) collagen chains in the basement membrane of basal cell carcinoma

Type IV collagen, the major component of basement membrane, consists primarily of ·1(IV) and ·2(IV) chains. Recently, other types of collagen IV chains, i.e. ·3(IV), ·4(IV), ·5(IV) and ·6(IV) chains, have been identified by protein chemistry and molecular cloning. We have examined the diversity of the assembly of ·(IV) chains of the basement membrane surrounding tumour nests of basal cell carcinomas, in tissues from 11 patients, by immunohistochemical analysis using specific monoclonal antibodies to six ·(IV) chain. The immunostaining profile of each chain differed with respect to the histological subtypes of basal cell carcinoma. In the morphea-like subtype, which was more invasive, ·1(IV) and ·2(IV) chains were discontinuously stained, and ·5(IV) and ·6(IV) chains were entirely absent. However, in the superficial subtype, which was non-aggressive, ·1(IV), ·2(IV), ·5(IV) and ·6(IV) chains were well stained compared with the other subtypes of basal cell carcinoma. In addition, in the solid subtype, which showed slow growth and ulceration, ·1(IV) and ·2(IV) chains were continuously stained, and ·5(IV) and ·6(IV) chains were discontinuous or absent. The assembly of ·5(IV) and ·6(IV) chains into the basement membrane was inhibited in the solid and morphea subtypes of BCC. This differential expression of type IV collagen chains seems to be associated with the invasive potential of basal cell carcinoma This revised version was published online in November 2006 with corrections to the Cover Date.