Athila,a new retroelement from Arabidopsis thaliana

An analysis of Arabidopsis thaliana heterochromatic regions allowed the identification of a new family of retroelements called Athila. These 10.5 kb elements, representing ca. 0.3% of the genome, present several features of retrotransposons and retroviruses. Athila elements are flanked by 1.5 kb long terminal repeats (LTR) that are themselves bounded by 5 bp perfect inverted repeats. These LTRs start and end with the retroviral consensus 5TG...CA3 nucleotides. A putative tRNA-binding site and a polypurine tract are found adjacent to the 5 and 3 LTR respectively. The central domain is composed of two long open reading frames (ORFs) of 935 and 694 amino acids. Despite several indications of recent transposition activity, the translation of these ORFs failed to reveal significant homology with proteins associated to retrotransposition. We suggest that the Athila family could result from the transduction and dispersion of a cellular gene by a retrotransposon.     

Evolution of the LINE-like I element in the Drosophila melanogaster species subgroup

LINE-like retrotransposons, the so-called I elements, control the system of I-R (inducer-reactive) hybrid dysgenesis in Drosophila melanogaster. I elements are present in many Drosophila species. It has been suggested that active, complete I elements, located at different sites on the chromosomes, invaded natural populations of D. melanogaster recently (1920–1970). But old strains lacking active I elements have only defective I elements located in the chromocenter. We have cloned I elements from D. melanogaster and the melanogaster subgroup. In D. melanogaster, the nucleotide sequences of chromocentral I elements differed from those on chromosome arms by as much as 7%. All the I elements of D. mauritiana and D. sechellia are more closely related to the chromosomal I elements of D. melanogaster than to the chromocentral I elements in any species. No sequence difference was observed in the surveyed region between two chromosomal I elements isolated from D. melanogaster and one from D. simulans. These findings strongly support the idea that the defective chromocentral I elements of D. melanogaster originated before the species diverged and the chromosomal I elements were eliminated. The chromosomal I elements reinvaded natural populations of D. melanogaster recently, and were possibly introduced from D. simulans by horizontal transmission.     

The transposable element mariner can excise in non-drosophilid insects

Plasmid-based excision assays performed in embryos of two non-drosophilid species using the mariner transposable element from Drosophila mauritiana resulted in empty excision sites identical to those observed after the excision of mariner from D. mauritiana chromosomes. In the presence of the autonomous mariner element Mos1, excision products were recovered from D. melanogaster, D. mauritiana and the blowfly Lucilia cuprina. When a hsp82 heat shock promoter-Mos1 construct was used to supply mariner transposase, excision products were also recovered from the Queensland fruitfly Bactrocera tryoni. Analysis of DNA sequences at empty excision sites led us to hypothesise that the mariner excision/repair process involves the formation of a heteroduplex at the excision breakpoint. The success of these assays suggests that they will provide a valuable tool for assessing the ability of mariner and mariner-like elements to function in non-drosophilid insects and for investigating the basic mechanisms of mariner excision and repair.     

Emerging mechanisms of the behavioral effects of steroids

Within two models of steroid-modulated behavior, sodium appetite and sexual receptivity, novel mechanisms of steroid action have emerged. These include interactions between different types of steroid receptors, plasticity of synapses, activation of unliganded steroid receptors, and rapid effects of steroids. These mechanisms highlight the diversity of steroid action in the central nervous system.     

橡胶-砂仁复合系统生物产量、营养元素空间格局的研究

通过对橡胶与砂仁间作林和同龄纯胶林各层次各器官生物量及１０种营养元素含量的测定,对比研究了两种分乔木层生物量按径级分配,林分平均净生产量,营养元素的积累分布规律,林龄为３０ａ,间作龄为８ａ的胶砂间作林的总生物量为１３９．８５ｔ／ｈｍ＾２。其中乔木层占７２．７％,间作层占２２．６％,枯落物层占５．２％,与同龄纯胶林相比,乔木层提高了７．６％,枯落物层提高了３８．９％,两种林分乔木层地上部分生物量约占     

Distribution of transposable elements in neotropical species of Drosophila

The phylogenetic distribution of transposable families, P, gypsy, hobo, I, and mariner has been analyzed in 33 species of 11 groups of neotropical Drosophila and a Drosophilidae species Zygotrica vittimaculosa, using squash blot and dot blot. Genomic DNA of almost all neotropical species tested hybridized with gypsy probe and some species showed a particularly strong hybridization signal, as D. gaucha, D. virilis, and species of flavopilosa group. The hobo element was restricted to melanogaster group and some strains of D. willistoni. Only D. simulans DNA showed hybridization to mariner probe in all species tested and D. simulans and D. melanogaster showed hybridization with I element probe. P element homologous sequence was present in D. melanogaster and all species and strains of the willistoni and saltans groups tested. The presence of at least one P-homologous sequence was detected in Drosophila mediopunctata. This one was the only P-bearing species of all six tested from the tripunctata group. Four different pairs of primers homologous to segments of the canonical sequence of D. melanogaster's P were used to amplify specific sequences from D. mediopunctata DNA, showing the occurrence of seemingly well-conserved P-homologous sequences. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of Orthologous Retrovirus-Like Elements in the White-Footed Mouse,Peromyscus leucopus

Three loci in the genome of the white-footed mouse, Peromyscus leucopus, were examined for the presence or absence of orthologous copies of the retrovirus-like element mys using polymerase chain reaction. We examined these loci in 28 mice collected throughout the P. leucopus species range. Mys insertions were present in only one of the individuals examined at the mys-1 and mys-7 loci. Conversely, the mys-6 element was found in several individuals, but the presence of this element was limited to northern latitudes. Because the long terminal repeats (LTRs) of a given element are expected to be identical at the time of retrotransposition into the genome, and to accumulate changes over evolutionary time, within-element LTR sequence comparisons can be used to estimate the relative age of insertions. Within-element LTR differences are greater in mys-6 than in mys-1 or mys-7. The LTRs from orthologous mys-6 elements of six mice were sequenced. The alignment revealed 13 of the 22 differences between the right and left LTRs that were shared by all orthologous mys-6 sites, suggesting that relative to its time of insertion into the genome, mys-6 has only recently spread across the northern part of the species range. Received: 23 January 1996 / Accepted: 24 April 1996     

嗜热脂肪芽孢杆菌中转座因子IS5376的转座行为研究

ＩＳ５３７６和ＩＳ５３７７是在嗜热脂肪芽孢杆菌（Ｂａｃｉｌｕｓｓｔｅａｒｏｔｈｅｒｍｏｐｈｉｌｕｓ）中发现的两个转座因子。随机取样分析的结果说明,ＩＳ５３７６由ＣＵ２１染色体向质粒ｐＦＤＣ５和ｐＦＤＣ１２的转座受温度的影响,而ＩＳ５３７７则不。温度影响的原因还不清楚,从现有证据看来,这由ＩＳ５３７６本身的性质所决定。另外,测得ＩＳ５３７６的转座作用有一定程度的专一性,还测得转座后所造成的目标序列的顺向重复为４或５ｂｐ。     

Elemental signatures of human diets from the Georgia Bight

Multielement analysis was performed on bone samples extracted from the femora of 39 adults from three mortuary sites (Johns Mound, Santa Catalina de Guale, and Santa Catalina de Guale de Santa Meria) and time periods (late preagricultural, early contact, and late contact) in the Georgia Bight. This study was used to investigate whether elemental analysis would support or contradict other lines of data regarding diets and dietary change previously generated for the region. The data are in agreement with an earlier interpretation, based on stable isotopes, that dietary maize increases through time but fails to support the idea that marine resources decreased in importance. Rather, it appears that the wild plant food component of the diets decreases as maize increases in importance; throughout the sequence, marine resources comprise a significant portion of the diets. © 1995 Wiley-Liss, Inc.