Natural selection maintains the transcribed LTR retrotransposons in Nosema bombycis

Eight intact LTR retrotransposons (Nbrl-Nbr8) have been previously characterized from the genome of Nosema bombycis, a eu-karyotic parasite with a compact and reduced genome. Here we describe six novel transcribed Nbr elements (Nbr9-Nbrl4) identified through either cDNA library or RT-PCR. Like previously determined ones, all of them belong to the Ty3/Gypsy superfamily. Retro-transposon diversity and incomplete domains with insertions {Nbrll), deletions (Nbrll) and in-frame stop codons in coding regions (Nbr9) were detected, suggesting that both defective and loss events of LTR retrotransposon have happened in N. bombycis genome.Analysis of selection showed that strong purifying selection acts on all elements except Nbrll. This implies that selective pressure keeps both these Nbrs and their functions in genome. Interestingly, Nbrll is under positive selection and some positively selected codons were identified, indicating that new functionality might have evolved in the Nbrll retrotransposon. Unlike other transposable elements, Nbrll has integrated into a conserved syntenic block and probably resulted in the inversion of both flanking regions. This demonstrates that transposable element is an important factor for the reshuffling and evolution of their host genomes, and may be maintained under natural selection.     

Natural selection maintains the transcribed LTR retrotransposons in Nosema bombycis

Eight intact LTR retrotransposons(Nbr1?Nbr8)have been previously characterized from the genome of Nosema bombycis,a eu-karyotic parasite with a compact and reduced genome.Here we describe six novel transcribed Nbr elements(Nbr9?Nbr14)identified through either cDNA library or RT-PCR.Like previously determined ones,all of them belong to the Ty3/Gypsy superfamily.Retrotransposon diversity and incomplete domains with insertions(Nbr12),deletions(Nbr11)and in-frame stop codons in coding regions(Nbr9)were detected...     

水稻逆转录转座子RIRE10拷贝数与LTR区转录活性的鉴定

在水稻第四号染色体的长臂上鉴定了一个结构完整的Ty3型逆转录转座子RIRE10。RIRE10两LTR间的中间区域在gag pol的上游还包含另一个开放阅读框。通过RT PCR与Northern印迹杂交检测到来自LTR区的转录产物 ;根据点杂交结果 ,鉴定出包含中间区域的RIRE10成员的个数以及LTR区的拷贝数。除了 6 5个完整的逆转录转座子所具备的两个LTR外 ,水稻基因组还含有近 90 0个RIRE10的solo LTR。LTR区的转录以及导致solo LTR产生的同源重组可能影响了RIRE10成员在水稻基因组中的转座活性     

Evidence for the contribution of LTR retrotransposons to C. elegans gene evolution

LTR retrotransposons may be important contributors to host gene evolution because they contain regulatory and coding signals. In an effort to assess the possible contribution of LTR retrotransposons to C. elegans gene evolution, we searched upstream and downstream of LTR retrotransposon sequences for the presence of predicted genes. Sixty-three percent of LTR retrotransposon sequences (79/124) are located within 1 kb of a gene or within gene boundaries. Most gene-retrotransposon associations were located along the chromosome arms. Our results are consistent with the hypothesis that LTR retrotransposons have contributed to the structural and/or regulatory evolution of genes in C. elegans.     

Formation of solo-LTRs through unequal homologous recombination counterbalances amplifications of LTR retrotransposons in rice Oryza sativa L

We studied the dynamics of hopi, Retrosat1, and RIRE3, three gypsy-like long terminal repeat (LTR) retrotransposons, in Oryza sativa L. genome. For each family, we assessed the phenetic relationships of the copies and estimated the date of insertion of the complete copies through the evaluation of their LTR divergence. We show that within each family, distinct phenetic groups have inserted at significantly different times, within the past 5 Myr and that two major amplification events may have occurred during this period. We show that solo-LTR formation through homologous unequal recombination has occurred in rice within the past 5 Myr for the three elements. We thus propose an increase/decrease model for rice genome evolution, in which both amplification and recombination processes drive variations in genome size.     

Identification and Characterization of Rhizot,a Novel LTR Retrotransposon of Rhizopus oryzae and R. delemar

A novel retrotransposon Rhizot was identified in Rhizopus oryzae and R. delemar. Rhizot has a unique structure that consists of a pol ORF similar to non-LTR (long terminal repeat) retorotransposons between two LTRs. Rhizot was distributed in all Rhizopus species tested. The Rhizot pol gene was transcribed in the liquid culture, and was induced by UV and oxidative stress.     

LTR Retrotransposon-Gene Associations in Drosophila melanogaster

Thirty-three percent (228/682) of all long terminal repeat (LTR) retrotransposon sequences (LRSs) present in the sequenced Drosophila melanogaster genome were found to be located in or within 1000 bp of a gene. Recently inserted LTR retrotransposons are significantly more likely to be located in or within genes than are older, fragmented LTR retrotransposon sequences, indicating that most LRS-gene associations are selected against over evolutionary time. LRSs associated with conserved genes (homologenes) are especially prone to negative selection. In contrast, fragmented LRSs that have persisted in the genome over long spans of evolutionary time are preferentially associated with genes involved in signal transduction and other newly evolved functions. Reviewing Editor: Dr. Juergen Brosius     

Evolution of the large genome in Capsicum annuum occurred through accumulation of single-type long terminal repeat retrotransposons and their derivatives

Although plant genome sizes are extremely diverse, the mechanism underlying the expansion of huge genomes that did not experience whole‐genome duplication has not been elucidated. The pepper, Capsicum annuum, is an excellent model for studies of genome expansion due to its large genome size (2700 Mb) and the absence of whole genome duplication. As most of the pepper genome structure has been identified as constitutive heterochromatin, we investigated the evolution of this region in detail. Our findings show that the constitutive heterochromatin in pepper was actively expanded 20.0–7.5 million years ago through a massive accumulation of single‐type Ty3/Gypsy‐like elements that belong to the Del subgroup. Interestingly, derivatives of the Del elements, such as non‐autonomous long terminal repeat retrotransposons and long‐unit tandem repeats, played important roles in the expansion of constitutive heterochromatic regions. This expansion occurred not only in the existing heterochromatic regions but also into the euchromatic regions. Furthermore, our results revealed a repeat of unit length 18–24 kb. This repeat was found not only in the pepper genome but also in the other solanaceous species, such as potato and tomato. These results represent a characteristic mechanism for large genome evolution in plants.     

水稻基因组中一类具有潜在转座活性的Solo—LTR的结构分析和鉴定

在水稻4号染色体两个BAC克隆序列分析中,发现了两个solo-LTR,分别命名为SLTR1和SLTR2。它们分别位于水稻18S rRNA基因和一逆转座子内部。序列比较发现,SLTR1和SLTR2存在着较高的同源性,并与水稻逆转座子RIRE8的LTR序列高度同源,分别为89.1%和70.1%。它们属于一类水稻gypsy类型逆转座子。利用SLTR1和SLTR2与水稻DNA杂交,结果显示两者广泛分布于水稻基因组中,是一类高拷贝重复序列。分别利用SLTR1和SLTR2的两侧特异性序列设计引物进行PCR扩增,结果发现在基因组的相应位置并不存在SLTR1或SLTR2;利用它们两侧被打断基因的特异性片段杂交基因组DNA,得到了同样的结果。这意味着SLTR1和SLTR2来源于基因组的其它位置,并通过某种转座的过程进入18S rRNA基因和另一逆转座子内部。Solo-LTR存在着这种潜在的转座活性,对于进一步研究solo-LTR的来源以及其在基因组进货和基因的表达调控中具有一定的意义。     

HIV—1长末端重复序列对重组痘苗病毒表达Gag蛋白的影响

将系列缺失的ＨＩＶ１长末端重复序列（ＬＴＲ）和全长的ｇａｇＯＲＦ置于痘苗病毒载体中,经同源重组和血球吸附试验,成功地构建了６株重组痘苗病毒。免疫印迹和免疫酶试验检测均表明,６株重组病毒的Ｇａｇ蛋白表达量因ＬＴＲ不同而有明显差异,表明ＨＩＶ１的ＬＴＲ及其下游基因置于痘病毒启动子控制下,在痘苗病毒中表达时有下述特点：（１）不同的痘苗病毒启动子与全长ＬＴＲ相互作用,对ｇａｇ基因表达有显著不同的调控效果;（２）ＮＲ序列对Ｇａｇ蛋白表达没有明显影响;（３）ＥＮ序列不能被重组痘苗病毒表达系统识别;（４）ＴＡＲ序列可提高Ｇａｇ蛋白的表达量;（５）Ｕ５区及下游非翻译序列不影响Ｇａｇ蛋白的表达。     

猪esr基因反转录转座子插入多态性及其与大白猪生产性能的关联性分析

雌激素受体(Estrogen receptor,esr)介导雌激素影响相关基因表达,从而调控哺乳动物的生长和繁殖机能.为了探讨esr基因的反转录转座子多态性对猪生长性能的影响,文中应用比较基因组学和生物信息学方法,预测猪esr基因的反转录转座子插入位点,采用PCR方法验证不同品种猪中插入多态性,并将该基因型与大白猪性能...     

Retrotransposon mdg3 Is Transferred between Somatic Cells of Unrelated Species in Mixed Culture

Since retrovirus-like particles of gypsy (mdg4) are capable of interspecific transfer, other Drosophila melanogaster gypsy-related retrotransposons were tested for this property. As a donor and a recipient, D. melanogaster and D. virilis cultured cells were used. Recipient cell DNA was analyzed with probes directed to mdg1, mdg3, 17.6, 297, 412, or B104/roo. Transfer was demonstrated for mdg3, which lacks env. The possible mechanism of transfer is discussed.