Homologous sequences in the Campoletis sonorensis polydnavirus genome are implicated in replication and nesting of the W segment family
Homologous sequences in the Campoletis sonorensis polydnavirus genome are implicated in replication and nesting of the W segment family
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DOI：
10.1128/jvi.71.11.8504-8513.1997
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发表时间：
1997-11-01
影响因子：
5.4
通讯作者：
Webb, BA
中科院分区：
文献类型：
--
作者：
Cui, LW;Webb, BA
多脱氧核糖核酸病毒（Polydnavirus，PDV）是一种基因组分段的双链DNA病毒，仅在某些种类的寄生蜂的输卵管中复制，是成功寄生鳞翅目昆虫所必需的。PDV DNA片段整合在其相关黄蜂宿主的基因组中，并且一些是嵌套的;即，较小的区段由较大的区段产生，并与较大的区段大致共线。为了确定嵌套病毒区段的内部结构，确定了PDV基因组区段及其整合位点的第一个完整核苷酸序列。通过限制性内切酶图谱、Southern杂交和序列分析，我们证明了Campoletissonorensis PDV片段W整合到黄蜂基因组DNA中。DNA序列分析表明，前病毒片段W在黄蜂染色体上终止于两个1，185-bp的直接长末端重复序列（LTR），而在染色体外（病毒）W中仅存在一个LTR拷贝。结果表明，末端同向重复序列是PDV DNA片段整合的一般特征，但重复序列的同源性和大小可以广泛变化。片段W在89 ~ 1.9kbp之间含有6种不同类型的12个不完全重复序列，同源性为65 ~ 90%。重复序列的方向和结构表明，W本身可能是通过序列重复和随后的分歧而产生的。克隆的R和M的作图、杂交和序列分析表明，这些片段嵌套在片段W内，并且一种类型的内部不完全直接重复序列牵涉到产生片段R和M的同源分子内重组事件。有趣的是，片段嵌套差异增加了由片段W编码的基因的拷贝数，这表明PDV的不寻常的基因组组织可能直接与该病毒在其与寄生蜂的专性互利关系中的独特功能有关。
Polydnaviruses (PDVs) are double-stranded DNA viruses with segmented genomes that replicate only in the oviducts of some species of parasitic wasps and are required for the successful parasitization of lepidopteran insects. PDV DNA segments are integrated in the genomes of their associated wasp hosts, and some are nested; i.e., smaller segments are produced from and largely colinear with larger segments, To determine the internal structure of nested viral segments, the first complete nucleotide sequence of a PDV genome segment and its integration locus was determined. By restriction mapping, Southern blot, and sequence analyses, we demonstrated that the Campoletis sonorensis PDV segment W is integrated into wasp genomic DNA. DNA sequence analysis revealed that proviral segment W terminates in two 1,185-bp direct long terminal repeats (LTRs) in the wasp chromosome, while only one LTR copy is present in the extrachromosomal (viral) W. The results suggest that terminal direct repeats are a general feature of PDV DNA segment integration but that the homology and size of the repeats can vary extensively. Segment W contains 12 imperfect direct repeats of six different types between 89 bp and 1.9 kbp with 65 to 90% homology. The orientation and structure of the repeats suggest that W itself may have arisen through sequence duplication and subsequent divergence. Mapping, hybridization, and sequence analyses of cloned R and M demonstrated that these segments are nested within segment W and that internal imperfect direct repeats of one type are implicated in the homologous intramolecular recombination events that generate segments R and M. Interestingly, segment nesting differentially increases the copy number of genes encoded by segment W, suggesting that the unusual genomic organization of PDVs may be directly linked to the unique functions of this virus in its obligate mutualistic association with parasitic wasps.