A transposon with an unusual LTR arrangement from Chlamydomonas reinhardtii contains an internal tandem array of 76 bp repeats.

TOC1, a transposable element from Chlamydomonas reinhardtii, is 5662 bases long. The 217 and 237 base long terminal repeat sequences of TOC1 are unusually arranged around the 4600 and 123 base unique regions: [217]-4600-[237] [217]-123-[237]. Although TOC1 contains long terminal repeats and most TOC1 elements are complete, features shared with virus-like retroposons, its unique 4600 base region is more similar to the structure of the L1 family of non-virus retroposons: first, 11 3/4 tandemly repeated copies of a 76 base repeat are found 813 bases from the left end of TOC1, and second using the universal genetic code large open reading frames were not found in TOC1. The relationship between TOC1, virus-like retroposons and the L1 family of non-virus retroposons is unclear and may be very distant since only poor similarity was found between the TOC1 encoded ORFs and retrovirus polypeptides. The length of the tandem array of 76 base repeat sequences was conserved in most TOC1 elements and solo 76 base repeat sequences were not found outside TOC1 elements in the C. reinhardtii genome. Nucleotide substitutions allow all copies of the 76 base repeat to be distinguished from one another.     

Structural organization of the human gastrointestinal glutathione peroxidase (GPX2) promoter and 3'-nontranscribed region: transcriptional response to exogenous redox agents

We describe a new family of repetitive elements, named Mimo, from the mosquito Culex pipiens. Structural characteristics of these elements fit well with those of miniature inverted-repeat transposable elements (MITEs), which are ubiquitous and highly abundant in plant genomes. The occurrence of Mimo in C. pipiens provides new evidence that MITEs are not restricted to plant genomes, but may be widespread in arthropods as well. The copy number of Mimo elements in C. pipiens (1000 copies in a 540 Mb genome) supports the hypothesis that there is a positive correlation between genome size and the magnitude of MITE proliferation. In contrast to most MITE families described so far, members of the Mimo family share a high sequence conservation, which may reflect a recent amplification history in this species. In addition, we found that Mimo elements are a frequent nest for other MITE-like elements, suggesting that multiple and successive MITE transposition events have occurred very recently in the C. pipiens genome. Despite evidence for recent mobility of these MITEs, no element has been found to encode a protein; therefore, we do not know how they have transposed and have spread in the genome. However, some sequence similarities in terminal inverted-repeats suggest a possible filiation of some of these mosquito MITEs with pogo-like DNA transposons.     

马铃薯StCRKs基因家族的鉴定分析及响应逆境信号的表达

为鉴定马铃薯（Solanum tuberosum）中富含半胱氨酸的类受体激酶（cysteine-rich receptor-like kinase,CRKs）,利用Pfam等工具对马铃薯蛋白质组和基因组序列进行分析,共鉴定到18个新的马铃薯StCRKs家族基因,这些基因分布在1、2、11和12号染色体上,均具有典型保守的CRK结构域。StCRKs基因的启动子区具有响应5种植物激素、昼夜节律、生物胁迫、非生物胁迫及种子特异性的响应元件。利用qRT-PCR方法对马铃薯盆栽苗开花期的根、茎、叶和花中的18个StCRKs基因进行组织特异性表达分析,结果显示不同基因的表达部位不同。分别用水杨酸类似物BTH和4 ℃低温处理马铃薯,有13个StCRKs基因能够响应低温信号,10个StCRKs基因能够被水杨酸类似物BTH诱导。为进一步深入研究StCRKs在生物胁迫及非生物胁迫中的功能提供了线索。     

SINEs: Short interspersed repeated elements of the eukaryotic genome

Much of the eukaryotic genome is composed of a variety of repetitive sequences. Amongst these, there are two kinds of retroposons (sequence elements derived from nonviral cellular RNA): SINEs (short interspersed elements) and LINEs (long interspersed elements). Amplification of SINEs occurs in a single germ cell, and the members of SINEs spread and become fixed in populations through genetic drift. SINEs can be regarded as phylogenetic landmarks: they are specific to one species, a few species, a genus or in some cases a family, indicating a specific time of amplification during evolution. Recent studies concerning the structure and origin of many SINEs revealed that retroposons are more widespread in animal genomes than was previously thought.     

Fragmentation heterogeneity of 23S ribosomal RNA in Haemophilus species

The fragmentation of 23S rRNA of 22 Haemophilus influenzae strains and eight strains belonging to other Haemophilus species was investigated. Instead of intact molecules, the 23S rRNA molecules were found to be cleaved into two to five smaller conserved fragments in most strains examined, especially in H. influenzae type b (5/6) and nontypeable strains (5/5). One or two conserved potential cleavage sites were identified by PCR analysis of the strains showing a fragmented 23S rRNA pattern. The relevant nucleotide sequences were determined and compared to H. influenzae Rd, which contains intact 23S rRNA molecules. An identical 112 bp long intervening sequence (IVS) at position 542 and a conserved 121–123 bp IVS sequence at position 1171 were found in two H. influenzae type b strains and one nontypeable strain. Among the strains with fragmented 23S rRNA, nearly half showed a heterogeneous cleavage pattern due to the dispersion of IVSs among different 23S rRNA operons. The localization of the conserved H. influenzae IVSs coincided well with the extensively studied IVSs among other bacteria, but differed in nucleotide sequence from any other reported IVSs. Therefore, the IVSs of Haemophilus 23S rRNA may originate from a common source that is independent of other bacteria.     

海南岛蚯蚓物种组成及其系统发育分析

海南岛独特的地理位置和复杂的古地理事件使其成为我国生物多样性的热点地区。已有的海南岛蚯蚓资料显示, 该岛的蚯蚓区系十分特殊, 且与大陆地区蚯蚓存在扩散与迁移。然而, 当海南岛与周围大陆断开形成独立岛屿后, 海南岛蚯蚓如何为适应海南岛的环境而逐渐形成现在岛内的分布与区系, 仍然是一个值得研究和探讨的问题。因此, 本研究在海南岛全面调查和采集蚯蚓标本, 整理海南岛地区的蚯蚓物种组成及其地理分布特征, 并联合5个线粒体基因COⅠ、COⅡ、ND1、12S rRNA和16S rRNA构建海南岛蚯蚓的分子系统发育树, 推测其分化时间和祖先分布区域, 探讨海南岛蚯蚓在岛内的分化与扩散过程。研究结果表明: (1)海南岛共有蚯蚓6科9属122种, 巨蚓科蚯蚓为优势科, 且全部为环毛类蚯蚓, 其中103种为海南岛特有种。蚯蚓物种数沿海拔呈先增加后减少的趋势, 在800‒1,000 m最大; (2)海南岛环毛类蚯蚓不同水平的遗传距离与我国巨蚓科蚯蚓的遗传距离区间基本一致。物种水平上, 美丽远盲蚓(Amynthas scitulus*)与纬向远盲蚓(A. zonarius)的基因遗传距离最小。在亚种水平, 保宁腔蚓指名亚种(Metaphire magna magna)和保宁腔蚓小型亚种(M. magna minuscula)的遗传距离均接近整体的物种水平。在种群水平, 等毛远盲蚓(A. homosetus)不同种群间遗传距离均接近整体的亚种水平; (3)海南岛环毛类蚯蚓可划分为7个类群, 其祖先于68.26 Ma开始分化, 可能起源于吊罗山。在新生代, 7个类群均得到较大发展。通过对海南岛蚯蚓组成及系统发育的梳理, 不仅为我国蚯蚓物种多样性研究提供基础资料, 也为岛屿蚯蚓物种系统发育关系分析提供科学参考。     

白桦APETALA2基因启动子的克隆及其表达分析

APETALA2（AP2）转录因子亚家族普遍存在于植物中,参与植株的生长发育、胁迫应答和多种生理生化反应的信号传导。本研究从白桦（Betula platyphylla Suk.）基因组中克隆了AP2基因2 308 bp的启动子序列,生物信息学分析发现,该序列除具有TATA-box和CAAT box等高等植物普遍具有的保守元件外,还具有大量光响应元件和激素响应元件,如响应赤霉素、脱落酸、茉莉酸甲酯等的元件。将白桦AP2基因启动子克隆至pBI121-35S：：GUS植物表达载体中,命名为pBI121-proAP2：：GUS,用农杆菌介导法侵染白桦和拟南芥,并进行GUS染色分析,结果表明AP2基因启动子驱动下的GUS报告基因在整个拟南芥中都表达,在白桦的营养器官和雌花种翅及花柄中也有表达,说明其具有启动活性,可能参与该器官的发育。     

Short Retroposons of the B2 Superfamily: Evolution and Application for the Study of Rodent Phylogeny

Short retroposons can be used as natural phylogenetic markers. By means of hybridization and PCR analysis, we demonstrate that B2 retroposon copies are present only in the three rodent families: Muridae, Cricetidae, and Spalacidae. This observation highlights the close phylogenetic relation between these families. Two novel B2-related retroposon families, named DIP and MEN elements, are described. DIP elements are found only in the genomes of jerboas (family Dipodidae) and birch mice (family Zapodidae), demonstrating the close relationship between these rodents. MEN element copies were isolated from the squirrel, Menetes berdmorei, but were not detected in three other species from the family Sciuridae. The MEN element has an unusual dimeric structure: the left and right monomers are B2- and B1-related sequences, respectively. Comparison of the B2, DIP, MEN, and 4.5S₁ RNA elements revealed an 80-bp core sequence located at the beginning of the B2 superfamily retroposons. This observation suggests that these retroposon families descended from a common progenitor. A likely candidate for this direct progenitor could be the ID retroposon. Received: 20 December 1996 / Accepted: 17 June 1997