Vink C, Beuken E, Bruggeman C A
Department of Medical Microbiology, University of Limburg, The Netherlands.
J Virol. 1996 Aug;70(8):5221-9. doi: 10.1128/JVI.70.8.5221-5229.1996.
The lytic replication cycle of herpesviruses can be divided into the following three steps: (i) circularization, in which, after infection, the termini of the linear double-stranded viral genome are fused; (ii) replication, in which the circular DNA serves as template for DNA replication, which generates large DNA concatemers; and (iii) maturation, in which the concatemeric viral DNA is processed into unit-length genomes, which are packaged into capsids. Sequences at the termini of the linear virion DNA are thought to play a key role in both genome circularization and maturation. To investigate the mechanism of these processes in the replication of rat cytomegalovirus (RCMV), we cloned, sequenced, and characterized the genomic termini of this betaherpesvirus. Both RCMV genomic termini were found to contain a single copy of a direct terminal repeat (TR). The TR sequence is 504 bp in length, has a high GC content (76%), and is not repeated at internal sites within the RCMV genome. The TR comprises several small internal direct repeats as well as two sequences which are homologous to herpesvirus pac-1 and pac-2 sites, respectively. The organization of the RCMV TR is unique among cytomegaloviruses with respect to the position of the pac sequences: pac-1 is located near the left end of the TR, whereas pac-2 is present near the right end. Both RCMV DNA termini carry an extension of a single nucleotide at the 3' end. Since these nucleotides are complementary, circularization of the viral genome is likely to occur via a simple ligation reaction.
（i）环化，感染后，线性双链病毒基因组的末端融合；（ii）复制，环状DNA作为DNA复制的模板，产生大量DNA串联体；（iii）成熟，串联体病毒DNA被加工成单位长度的基因组，然后包装到衣壳中。线性病毒粒子DNA末端的序列被认为在基因组环化和成熟过程中都起着关键作用。为了研究大鼠巨细胞病毒（RCMV）复制过程中这些过程的机制，我们克隆、测序并鉴定了这种β疱疹病毒的基因组末端。发现RCMV基因组的两个末端都包含一个直接末端重复序列（TR）的单拷贝。TR序列长度为504 bp，GC含量高（76%），在RCMV基因组内部位点不重复。TR包含几个小的内部直接重复序列以及两个分别与疱疹病毒pac-1和pac-2位点同源的序列。就pac序列的位置而言，RCMV TR的组织在巨细胞病毒中是独特的：pac-1位于TR的左端附近，而pac-2位于右端附近。RCMV DNA的两个末端在3'端都有一个单核苷酸的延伸。由于这些核苷酸是互补的，病毒基因组的环化可能通过简单的连接反应发生。
