The in situ formation of DNA · DNA duplexes of Drosophila virilis satellite DNA

The DNA of Drosophila virilis brains and imaginal discs was labeled in vitro to a specific activity of 6 X 10(-5) dpm/mug, using an organ culture medium. The DNA was fractionated on neutral and alkaline CsC1 gradients and the heavy strands of satellite I annealed in situ to denatured polytene chromosomes from squash preparations of larval salivary glands. Nuclease S1 from Aspergillus oryzae was used to digest the unpaired ssDNA, resulting in a distinct labeling of the alpha-heterochromatin in the chromocenter and a small amount of diffused labeling in the proximal beta-heterochromatic part of the X-Chromsome.     

维生素C·Cu·菲咯啉系统对DNA的定位损伤

维生素Ｃ·Ｃｕ·菲咯啉系统对ＤＮＡ的定位损伤柯德森,王爱国,罗广华（中国科学院华南植物研究所,广州５１０６５０）关键词活性氧;ＤＮＡ;定位损伤活性氧对ＤＮＡ的损伤已经被很多工作所证实”””,这种伤害是由０Ｂ”直接作用于ＤＮＡ所引起的”’“。但是ＯＨ’...     

DNA的“第一夫人”——罗莎琳德·富兰克林

2010年4月25日是DNA双螺旋结构发现的57周年纪念日,全世界都在举行隆重的纪念活动。在我们为沃森和克里克的伟大发现欢欣鼓舞的时候,我们也应该纪念曾经为这一发现做出突出贡献、被称为DNA的"第一夫人"的罗莎琳德·富兰克林(Rosalind Franklin)。本文简要介绍了富兰克林短暂而又富于贡献的一生,希望大家能够了解她为DNA双螺旋结构的发现所作的功勋。     

H···N hydrogen bond lengths in double stranded DNA from internucleotide dipolar couplings

The ratio of the internucleotide dipolar coupling and the corresponding one-bond imino ¹⁵N-¹H dipolar coupling provides a measure for the N···H/H-N distance ratio. Measurements were carried out for a dodecamer, d(CGCGAATTCGCG)₂, in which a C-G and an A-T basepair were uniformly enriched in ¹⁵N. When assuming H-bonds to be perfectly linear, dipolar data indicate time-averaged hydrogen bond lengths of 1.80±0.03 Å for A-T and 1.86±0.02 Å for C-G. When using H-bond orientations from high resolution X-ray data, H-bond lengths are about 0.1 Å shorter.     

Flexibility of A · Pairs in Left-Handed DNA Helices

Abstract

We have analysed by various approaches the structure of cloned synthetic sequences in supercoiled plasmids. Individual inserts were formed by d(C-G)_n blocks interrupted by the presence of A · T pairs positioned either in phase or out of phase of pur-pyr alternation. Based on the thermodynamic analysis we obtained results confirming that A · T pairs are easily incorporated into left-handed helices without significant energetic penalty. Sequences GTAC which are known to form cruciform structures in multiple repetition underwent a B-Z transition. In the case of plasmids containing AA/TT code words and substantial discontinuities in purine-pyrimidine alternation our analysis indicates that Z-Z junctions formed by A · T pairs contributed little to the overall energetic demands of the B-Z transition probably thanks to their high conformational flexibility.     

弗雷德里克·桑格(Frederick Sanger)看到的蛋白质和DNA

<正>2013年11月19日桑格去世,享年95岁。对于任何一个人,能够获得一次诺贝尔奖就已经是伟大的成就,如果获得两次,那绝对是可遇而不可求的事。桑格与居里夫人、约翰·巴丁(John Bardeen)以及莱纳斯·鲍林(Linus Pauling)一起构成了大概是人类社会中最难加入的"两次诺贝尔奖获得者俱乐部",也是一个"四人帮"了。在桑格的一生中,他还获得过其他许多的荣誉和头衔,然而所有这些荣誉和头衔都难以与他对现代生命科     

Sequence-dependent conformational heterogeneity of a hybrid DNA·RNA dodecamer duplex

Summary Two- and three-dimensional homonuclear NMR studies of a hybrid duplex RI, formed by annealing r(GCGCAAAACGCG) and d(CGCGTTTTGCGC) strands are described. NMR parameters, such as intra-and interresidue proton-proton NOEs and sugar proton coupling constants were analyzed with reference to those of the corresponding DNA·DNA duplex. Furthermore, spectral analyses were conducted on the basis of model structures of nucleic acid duplexes. Distinctive spectral patterns of the hybrid duplex reveal unique heterogeneous conformations which co-exist throughtout the sequence and are significantly different from those of model structures of either canonical A- or B-forms. Features of an intermediate conformation were observed in the DNA and RNA strands in duplex RI, the former being more B-like and the latter more A-like. Three-dimensional NOESY-NOESY spectra were analyzed and their use was demonstrated for resolving superimposed resonances and cross peaks, especially those originating from the RNA strand. The application of a useful strategy that combines the use of 2D NMR data and the known structural information for efficient 3D spectral analyses is demonstrated.     

Fluorescence analysis of G·C versus A·T binding of quinacrine to DNA

The affinity of quinacrine for native DNA has been determined from fluorescence measurements and equilibrium dialysis in Tris-HC10.05 m, NaCl0.1 m, EDTA 10^?3m, pH 7.5. When considering M. lysodeiktikus, E. coli calf thymus and C. perfringens the affinities of DNA for quaniactive have been found to change by a factor of two and the fluorescence intensities to change by a factor of 25. The varying affinities and fluoroescence intensities of bound quinacrine are attributed to heterogeneous binding. For all DNAs we have assumed that there exist three classes of intercalation sites: I, A·T-A·T; 2, G·C-G·C; and 3, A·T-G·C, assuming that base pair ordering is less relevant than base composition of sites. By fitting the affinities of native DNAs with this model it was found that quinacrine binds to site 2 three times more strongly than it does to site 1. When flucrescence intensity is studied, triplets of A·T pairs appear to be responsible for the high quantum yield of A·T rich DNA whereas the quenching properties of a G·C base pair adjacent to an intercalated quinacrine are well known.     

植物细胞核DNA,叶绿体DNA和线粒体DNA的比较

植物一般有细胞核,叶绿体和线粒体三套遗传体系,本文结合近年来植物分子生物学研究的最新进展,系统比较了细胞核ＤＮＡ,叶绿体ＤＮＡ和线粒体ＤＮＡ在组织结构,遗传方式,基因表达（转录,翻译,ＲＮＡ加工）等方面的差异。     

DNA化学合成和DNA重组的研究

DNA化学合成已用于很多DNA重组研究中,这些应用包括功能基因全合成和克隆、自然基因的克隆和表达、通过定向突变,剪辑和改变基因。