Bigot Yves, Stasiak Karine, Rouleux-Bonnin Florence, Federici Brian A
Department of Entomology and Interdepartmental Graduate Program in Genetics, University of California, Riverside, CA 92521, USA2.
IRBI, Groupe d'Etude des Parasites Moléculaires, UPRESA CNRS 6035, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France1.
J Gen Virol. 2000 Dec;81(Pt 12):3073-3082. doi: 10.1099/0022-1317-81-12-3073.
The accompanying phylogenetic study of large double-stranded DNA viruses based on their delta DNA polymerase genes suggests that ascoviruses (family ASCOVIRIDAE:) and iridoviruses (family IRIDOVIRIDAE:) are closely related and may share a common ancestor. This relationship was unexpected because of marked differences between these viruses. Iridoviruses produce icosahedral virions and occur broadly among vertebrates and invertebrates, whereas ascoviruses typically produce reniform or bacilliform virions and are restricted to insect hosts, primarily lepidopterans. Detailed comparisons of these two virus types are not possible because fundamental information on the properties of the virions and their genomes is lacking, especially for ascoviruses. To facilitate further investigation of the putative evolutionary relationship between ascoviruses and iridoviruses, the genomes of representative viruses from each family were compared with respect to physical configuration, presence of DNA repeats and degree of DNA methylation. Genomes from Spodoptera frugiperda (SfAV1), Heliothis virescens (HvAV3) and Diadromus pulchellus (DpAV4) ascoviruses were all found to be circular and partially superhelical and to contain large interspersed repeats of 1-3 kbp. Mosquito (IV type 3), lepidopteran (IV type 6) and isopod (IV type 31) iridovirus genomes were all linear and lacked large regions of repetitive DNA. Ascovirus and iridovirus genomes were methylated and one, DpAV4, had the highest degree of methylation of any reported animal DNA virus. The major differences in the physical and biochemical characteristics of ascoviruses and iridoviruses reported here provide a foundation for further studies of their relatedness while making their possible close relationship and divergence during evolution of even greater interest.
基于双链DNA病毒的δDNA聚合酶基因进行的系统发育研究表明， ascoviruses（ASCOVIRIDAE科）和虹彩病毒（IRIDOVIRIDAE科）密切相关，可能有共同的祖先。这种关系出人意料，因为这些病毒之间存在明显差异。虹彩病毒产生二十面体病毒粒子，广泛存在于脊椎动物和无脊椎动物中，而ascoviruses通常产生肾形或杆状病毒粒子，仅限于昆虫宿主，主要是鳞翅目昆虫。由于缺乏关于病毒粒子及其基因组特性的基本信息，特别是关于ascoviruses的信息，无法对这两种病毒类型进行详细比较。为了便于进一步研究ascoviruses和虹彩病毒之间假定的进化关系，对每个科的代表性病毒基因组在物理结构、DNA重复序列的存在和DNA甲基化程度方面进行了比较。发现草地贪夜蛾（SfAV1）、棉铃虫（HvAV3）和小茧蜂（DpAV4）的ascovirus基因组都是环状的，部分呈超螺旋状，并且包含1-3kbp的大散在重复序列。蚊子（IV型3）、鳞翅目昆虫（IV型6）和等足类动物（IV型31）的虹彩病毒基因组都是线性的，缺乏大片段的重复DNA。ascovirus和虹彩病毒基因组都被甲基化，其中一种，DpAV4，在所有报道的动物DNA病毒中甲基化程度最高。本文报道的ascoviruses和虹彩病毒在物理和生化特征上的主要差异为进一步研究它们的亲缘关系提供了基础，同时也使它们在进化过程中可能存在的密切关系和分化更具研究价值。
