5_S rRNA分子进化的研究

截至目前为止,人们已测出了300余种5SrRNA分子的一级结构。本文在其中选择了具有代表性的脊椎动物、无脊椎动物、原生动物以及植物和细菌等共130个种的5SrRNA一级结构,通过运用分子进化研究中的“今祖法”,在TRS—80型微机上,进行了比较和计算,作出了相应的系统树,并得到了与其它一些研究结果基本一致的结论。同时,讨论了分子进化的研究本身以及“今祖法”在分子进化研究中的问题和局限性。     

脊髓灰质炎病毒的分子进化

本文根据脊髓灰质炎病毒3个型别参考毒株的基因组核苷酸序列和蛋白质氨基酸序列资料,首次试用Kimura的分子进化理论和计算方法,推算出脊髓灰质炎病毒型间的进化距离、分歧进化时间及病毒蛋白质氨基酸的替换率。结果表明:(1)型间毒株相互进化距离大致相等;(2)三个型病毒是由一个共同祖先病毒在距今约1—2千年以前几乎同时分歧进化而来;(3)型间毒株蛋白质氨基酸替换率也大致相等。     

蕨类植物psaA基因的分子进化研究

采用“放松分子钟”模型、氨基酸位点正选择模型和分子内共进化网络估算方法,对蕨类植物光合系统Ⅰ核心蛋白PSAA编码基因psaA的进化趋势进行了研究。结果显示,叶绿体基因psaA编码区全序列具备成为蕨类植物系统发育关系重建位点的潜力,与rbcL基因联合后能构建高后验概率的系统发育树;蕨类植物的PSAA蛋白中存在一些曾经历正选择的氨基酸位点,其中29个位点聚合成为16个共进化组,通过共进化网络的方式协同影响光合系统Ⅰ的内部调整,提升其在被子植物兴起后光合环境下的适应能力。本文对蕨类植物进化潜能与分子机理的研究结果为揭示蕨类植物适应新生境提供了科学依据,也为植物系统分类学研究提供了分子依据。     

麂属(Muntiacus)动物线粒体12SrRNA和细胞色素B基因序列分析及其分子进化关系

对麂属（Muntiacus)中的3种动物;赤麂（M.muntjak)（2n=6♀,7♂）,小麂（M.reevesi)(2n=46）,黑（M.crinifrons(2♀,9♂）线粒体DNA12SrRNA和细胞色素B783bp左右的片段进行序列分析,并根据序列信息建立分子系统树,同时探讨了这3种动物的起源,分类地位及进化关系。     

肌动蛋白与真核生物的进化

以肌动蛋白氨基酸取代与真核生物进化年代呈线性关系为依据，收集原生生物界，真菌界，植物界和动物界等四界７４种生物的１２８个肌动蛋白序列，通过对其氨基酸序列同源性进行比较，制作出肌动蛋白的分子进化树，并依此进化树从分子水平对真核生物的进化进行一些探讨，从总体上看，肌动蛋白分子进化树较地地反映了真核生物间的进化关系，为确定某些生物的进化位置及进化关系提供了分子证据。     

细胞色素分子疏水性与进化的关系

本文在先前研究结果的基础上,通过对细胞色素分子一维结构间疏水相似性的计算,建立了相应的分子系统树,并对细胞色素分子间的进化关系进行了探讨。结果表明,从蛋白质分子的疏水相似性和非线性三维结构来研究分子间的进货关系,不仅得到了与用其它方法所得到的结果基本一致的结论,而且还在一定程度上克服了其它一些方法的局限性,取得了较佳的结果。     

昆虫卵黄蛋白分子进化的研究进展

卵黄原蛋白（Vg）、卵黄多肽（YP）和小卵黄蛋白（minor YP）是昆虫三类主要的卵黄蛋白,它们之间的同源性一直是研究的重点。本文根据已经解析的Vg,YP和minor YP的氨基酸序列,采用序列比对和系统树分析的方法,并结合国内外对三者同源性研究的基础,对其进化关系进行了分析。结果表明,Vg,YP和minor YP是三类具有不同进化祖先的卵黄蛋白,它们的氨基酸序列相似性较低。Vg在系统进化过程中最为保守,与人类的血清载脂蛋白B(ApoB)具有较高的同源性;YP与脊椎动物的肝脂酶和胰脂酶具有较高的同源性;而minor YP与脊椎动物胃脂肪酶和舌脂肪酶具有较高的同源性。同时,对三者的分子特性做了简单的介绍。     

植物基因家族的分子进化

植物基因家族的分子进化曾庆平,郭勇（华南理工大学生物工程系,广州５１０６４１）关键词基因家族,同源性,分子进化,生物工程建立基因数据库与计算机检索程序使不同基因之间的碱基序列同源性的比较成为可能,同时也有助于进行基因的分子起源与进化以及蛋白质结构与功...     

分子进化研究:Ⅰ.细胞色素C分子进化的模糊聚类分析法研究

本文在强调生物系统自身特点的基础上,针对分子进化本身所具有的模糊性,运用模糊聚类分析的原理和方法,就29种动物细胞色素c一级结构间的进化关系进行了研究,作出了相应的分子系统树并运用硬划分法对该树进行了修改。同时,与其它一些研究的结果进行了比较,讨论了在生物大分子一级结构间进行比较、分析的局限性和分子进化研究中的一些有待解决的问题。     

中国地鼠线粒体Cyt b基因测序及其分子进化

目的测定中国地鼠线粒体DNA细胞色素b基因部分序列,分析其分子系统进化关系。方法提取中国地鼠肝脏的总基因组DNA。设计合成特异引物进行PCR扩增,经检测进行测序。用Blast与GenBank中啮齿类其他常用实验动物的物种细胞色素b基因进行同源序列比较,分析其碱基组成及变异情况,并用邻接法、最大简约法、最小进化法构建了分子系统树,在分子水平上探讨中国地鼠和常用啮齿类实验动物的进化关系。结果获得了中国地鼠线粒体Cytb基因的部分序列,共936bp。结论中国地鼠和金黄地鼠的亲缘关系最近,与小鼠、大鼠存在的差异相对大,与豚鼠的亲缘关系最远,与传统的分类地位基本吻合。     

蛋白质结构的分形及其与进化关系的研究

本文在应用分形理论对蛋白质分子结构的分形进行研究的基础上,从非线性角度,就蛋白质多肽链的结构与形以及球蛋白三维结构的分形与进化的关系问题,进行了理论探讨和分析。     

Stochastic fractal behavior in concentration fluctuation and fluorescence correlation spectroscopy.

Fluctuations in the concentration of Brownian particles in one and two dimensions, or any reasonable measurement of the concentration such as in fluorescence correlation spectroscopy, is shown to be a stochastic fractal with a long tail. Being singular at omega = 0, the power spectrum of the fluctuation S(omega) approximately omega-1/2 for diffusion in one dimension, approximately log omega in two dimensions, but non-singular in three dimensions. This discovery provides one simple physical mechanism for possible long-memory fractal behavior, and its implications to various biological processes are discussed.     

THE MOLECULAR EVOLUTION OF PITUITARY HORMONES

1. The pituitary hormones can be divided into 4 families; within each the members are structurally related and have probably evolved from a common ancestor by a process of gene duplication and divergence. 2. Recent structural studies have revealed much about the evolution of proteins. The roles of point mutation, gene duplication and partial gene duplication in molecular evolution have been highlighted, and the nature of the evolutionary forces involved has been extensively debated. The information available about the evolution of proteins in general provides a background for consideration of pituitary hormone evolution. 3. The structure and function of the mammalian neurohypophysial hormones (oxytocin and vasopressin) has been studied in detail. Related (structurally similar) peptides have been found in the neurohypophyses of lower vertebrates and have been Characterized in many instances. Several schemes have been proposed for the evolution of these hormones. 4. The vasopressins of the pig and its relatives show a genetic polymorphism. The roles of neurohypophysial hormones in lower vertebrates are very varied and not fully understood. 5. The ACTHs and MSHs are members of a second family of pituitary hormones. They are polypeptides of moderate size. Studies on amino-acid sequences have been carried out for ACTHs and MSHs from several mammals. α-MSH is identical in all cases studied in detail, but β-MSH and ACTH vary to some extent. There is considerable sequence homology between the hormones in this family - indicating a common phylogenetic origin and several gene duplications. 6. Dogfish MSH is the only non-mammalian hormone of the ACTH-MSH family to have been studied in detail. Two MSHs have been isolated from this species; both resemble the a-MSH of mammals in amino-acid sequence. ACTH-like and MSH-like hormones exist in many other vertebrate groups, but have not been characterized fully. 7. Structure-function relationships have been widely studied in the ACTH-MSH family, and have some interesting evolutionary implications. Polymorphism of P-MSHs is found in some mammals. 8. A third family of protein hormones includes pituitary prolactin and growth hormone, and placental lactogen. These are proteins of moderate size which have been shown to be widely distributed among the vertebrates. Species specificity can be recognized with regard to biological, immunological and structural properties. 9. Amino-acid sequences have been determined for growth hormones and prolactins from several mammals. There is sequence homology between growth hormone and prolactin. Human placental lactogen closely resembles human growth hormone. A phylogenetic tree has been constructed for this protein family. Rates of evolution within the group are rather variable. 10. The fourth family of pituitary hormones (FSH, LH, TSH and some related placental hormones) are all glycoproteins and have a subunit structure. Extensive sequence studies have been carried out on the hormones from some mammals, and show that there is considerable homology between the various subunits. The α-subunits of human TSH, LH and HCG (and probably FSH) are very similar. The β-subunits are different, but homologous. Evolution of this family clearly took place by a series of gene duplications followed by gene divergence. Schemes whereby this could have occurred have been discussed. Related hormones occur in lower vertebrates, but have not been fully characterized. Some lower vertebrates may possess only one gonado-trophin. 11. The pituitary hormones provide an interesting range of evolutionary problems, and are useful models for the study of molecular evolution. The evolutionary processes involved in their diversification have been discussed, with particular reference to the co-evolution of hormones and their receptors. Neutral mutations and gene duplications may have played a role in providing co-existing variation of hormones and receptors. 12. A speculative model for the evolution of neurohypophysial hormones is proposed, as an example of how molecular evolution may have operated in this and other hormone groups. 13. Homologies have been proposed between the various families of pituitary hormones, and between pituitary proteins and other entero-secretory proteins. The pituitary protein hormones were probably elaborated from smaller molecules by a process of partial gene duplication.     

Sequence and secondary structure of mouse 28S rRNA 5''terminal domain. Organisation of the 5.8S-28S rRNA complex.

We present the sequence of the 5' terminal 585 nucleotides of mouse 28S rRNA as inferred from the DNA sequence of a cloned gene fragment. The comparison of mouse 28S rRNA sequence with its yeast homolog, the only known complete sequence of eukaryotic nucleus-encoded large rRNA (see ref. 1, 2) reveals the strong conservation of two large stretches which are interspersed with completely divergent sequences. These two blocks of homology span the two segments which have been recently proposed to participate directly in the 5.8S-large rRNA complex in yeast (see ref. 1) through base-pairing with both termini of 5.8S rRNA. The validity of the proposed structural model for 5.8S-28S rRNA complex in eukaryotes is strongly supported by comparative analysis of mouse and yeast sequences: despite a number of mutations in 28S and 5.8S rRNA sequences in interacting regions, the secondary structure that can be proposed for mouse complex is perfectly identical with yeast's, with all the 41 base-pairings between the two molecules maintained through 11 pairs of compensatory base changes. The other regions of the mouse 28S rRNA 5'terminal domain, which have extensively diverged in primary sequence, can nevertheless be folded in a secondary structure pattern highly reminiscent of their yeast' homolog. A minor revision is proposed for mouse 5.8S rRNA sequence.     

Molecular evolution modeled as a fractal Poisson process in agreement with mammalian sequence comparisons

The fractal doubly stochastic Poisson process (FDSPP) model of molecular evolution, like other doubly stochastic Poisson models, agrees with the high estimates for the index of dispersion found from sequence comparisons. Unlike certain previous models, the FDSPP also predicts a positive geometric correlation between the index of dispersion and the mean number of substitutions. Such a relationship is statistically proven herein using comparisons between 49 mammalian genes. There is no characteristic rate associated with molecular evolution according to this model, but there is a scaling relationship in rates according to a fractal dimension of evolution. The FDSPP is a suitable replacement for the homogeneous Poisson process in tests of the lineage dependence of rates and in estimating confidence intervals for divergence times. As opposed to other fractal models, this model can be interpreted in terms of Darwinian selection and drift.      

台湾海峡鱼类绦虫的分子系统学研究

利用DNA测序技术对台湾海峡部分鱼类绦虫的16S rRNA和18S rRNA基因片段序列进行了分析。使用PAUP4·0b10软件构建的进化树显示,目前关于绦虫二叶目、锥吻目、假叶目、盘头目和四叶目的划分是比较合理的,绦虫进化基本遵循了头节形态从简单到复杂的进化规律。报道了国内首次发现的双叶目绦虫,进化树结果初步支持了巨槽属和棘头属的划分。此外,结果也支持了前孔属绦虫的分类地位。但是,对耳槽属绦虫与阶室属绦虫的形态学划分与分子系统学相矛盾,利用16S rRNA基因对盘头目各种的进化树分析与形态学差异很大,这些问题都需要更多研究来进行深入分析。     

Intermolecular hybridization of 5S rRNA with 18S rRNA: identification of a 5'-terminally-located nucleotide sequence in mouse 5S rRNA which base-pairs with two specific complementary sequences in 18S rRNA.

Eukaryotic 5S rRNA hybridizes specifically with 18S rRNA in vitro to form a stable intermolecular RNA:RNA hybrid. We have used 5S rRNA/18S rRNA fragment hybridization studies coupled with ribonuclease digestion and primer extension/chain termination analysis of 5S rRNA:18S rRNA hybrids to more completely map those mouse 5S rRNA and 18S rRNA sequences responsible for duplex formation. Fragment hybridization analysis has defined a 5'-terminal region of 5S rRNA (nucleotides 6-27) which base-pairs with two independent sequences in 18S rRNA designated Regions 1 (nucleotides 1157-1180) and 2 (nucleotides 1324-1339). Ribonuclease digestion of isolated 5S rRNA:18S rRNA hybrids with both single-strand- and double-strand-specific nucleases supports the involvement of this 5'-terminal 5S rRNA sequence in 18S rRNA hybridization. Primer extension/chain termination analysis of isolated 5S rRNA:18S rRNA hybrids confirms the base-pairing of 5S rRNA to the designated Regions 1 and 2 of 18S rRNA. Using these results, 5S rRNA:18S rRNA intermolecular hybrid structures are proposed. Comparative sequence analysis revealed the conservation of these hybrid structures in higher eukaryotes and the same but smaller core hybrid structures in lower eukaryotes and prokaryotes. This suggests that the 5S rRNA:16S/18S rRNA hybrids have been conserved in evolution for ribosome function.     

The structure of the yeast ribosomal RNA genes. 4. Complete sequence of the 25 S rRNA gene from Saccharomyces cerevisae.

The complete nucleotide sequence of the 25 S rRNA gene from one rDNA repeating unit of Saccharomyces cerevisiae has been determined. The corresponding 25 S rRNA molecule contains 3392 nucleotides and has an estimated relative molecular mass (Mr, Na-salt) or 1.17 x 10(6). Striking sequence homology is observed with known 5'- and 3'-end terminal segments of L-rRNA from other eukaryotes. Possible models of interaction with 5.8 S rRNA are discussed.     

The exosome of Trypanosoma brucei.

The yeast exosome is a complex of at least 10 essential 3'-5' riboexonucleases which is involved in 3'-processing of many RNA species. An exosome-like complex has been found or predicted to exist in other eukaryotes but not in Escherichia coli. The unicellular parasite Trypanosoma brucei diverged very early in eukaryotic evolution. We show here that T.brucei contains at least eight exosome subunit homologs, but only a subset of these associate in a complex. Accordingly, the T.brucei exosome is smaller than that of yeast. Both free and complex-associated homologs are essential for cell viability and are involved in 5.8S rRNA maturation. We suggest that the exosome was present in primitive eukaryotes, and became increasingly complex during subsequent evolution.