Schynts Frédéric, McVoy Michael A, Meurens François, Detry Bruno, Epstein Alberto L, Thiry Etienne
Department of Infectious and Parasitic Diseases, Laboratory of Virology, Faculty of Veterinary Medicine, University of Liège, Liège B-4000, Belgium.
Virology. 2003 Sep 15;314(1):326-35. doi: 10.1016/s0042-6822(03)00437-9.
Herpesvirus genomes are often characterized by the presence of direct and inverted repeats that delineate their grouping into six structural classes. Class D genomes consist of a long (L) segment and a short (S) segment. The latter is flanked by large inverted repeats. DNA replication produces concatemers of head-to-tail linked genomes that are cleaved into unit genomes during the process of packaging DNA into capsids. Packaged class D genomes are an equimolar mixture of two isomers in which S is in either of two orientations, presumably a consequence of homologous recombination between the inverted repeats. The L segment remains predominantly fixed in a prototype (P) orientation; however, low levels of genomes having inverted L (I(L)) segments have been reported for some class D herpesviruses. Inefficient formation of class D I(L) genomes has been attributed to infrequent L segment inversion, but recent detection of frequent inverted L segments in equine herpesvirus 1 concatemers [Virology 229 (1997) 415-420] suggests that the defect may be at the level of cleavage and packaging rather than inversion. In this study, the structures of virion and concatemeric DNA of another class D herpesvirus, bovine herpesvirus 1, were determined. Virion DNA contained low levels of I(L) genomes, whereas concatemeric DNA contained significant amounts of L segments in both P and I(L) orientations. However, concatemeric termini exhibited a preponderance of L termini derived from P isomers which was comparable to the preponderance of P genomes found in virion DNA. Thus, the defect in formation of I(L) genomes appears to lie at the level of concatemer cleavage. These results have important implications for the mechanisms by which herpesvirus DNA cleavage and packaging occur.
疱疹病毒基因组通常具有正向和反向重复序列，这些序列将它们分为六个结构类别。D类基因组由一个长（L）片段和一个短（S）片段组成。后者两侧是大的反向重复序列。DNA复制产生头尾相连的基因组串联体，在将DNA包装到衣壳的过程中被切割成单位基因组。包装的D类基因组是两种异构体的等摩尔混合物，其中S处于两种取向中的任何一种，这可能是反向重复序列之间同源重组的结果。L片段主要保持在原型（P）取向；然而，对于一些D类疱疹病毒，已经报道了具有反向L（I（L））片段的低水平基因组。D类I（L）基因组形成效率低下被归因于L片段的罕见倒位，但最近在马疱疹病毒1串联体中频繁检测到反向L片段[病毒学229（1997）415 - 420]表明，缺陷可能在于切割和包装水平而非倒位。在本研究中，确定了另一种D类疱疹病毒——牛疱疹病毒1的病毒粒子和串联体DNA的结构。病毒粒子DNA含有低水平的I（L）基因组，而串联体DNA含有大量处于P和I（L）取向的L片段。然而，串联体末端显示出源自P异构体的L末端占优势，这与在病毒粒子DNA中发现的P基因组占优势相当。因此，I（L）基因组形成的缺陷似乎在于串联体切割水平。这些结果对疱疹病毒DNA切割和包装发生的机制具有重要意义。
