Department of Microbiology, Perleman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
J Virol. 2012 Nov;86(22):12313-21. doi: 10.1128/JVI.01570-12. Epub 2012 Sep 5.
Herpes simplex virus (HSV) is a large DNA virus which is characterized by its ability to form latent infections in neurons of the peripheral nervous system. Although histones are found in the capsids of small DNA viruses (papovaviruses), none are found in the capsids of large HSV. However, after entry into the infected cell nucleus, the HSV genome begins to associate with nucleosomes during the earliest stages of infection. In contrast, late during infection, newly replicated viral DNA does not appear to associate with nucleosomes, suggesting that histones are deposited specifically on input viral DNA. The mechanisms of deposition and removing histones from the viral genome are unclear. Recently, histone chaperones, involved in the assembly and disassembly of nucleosomes, have been identified. Human antisilencing factor 1 (Asf1) is one such factor which is involved in both the assembly and disassembly of nucleosomes in cellular systems. In this study, we have examined the effect of small interfering RNA (siRNA) knockdown of Asf1a on HSV infections in HeLa cells. Both viral replication and growth were found to be decreased. Also, viral DNA was significantly less protected from micrococcal nuclease (MNase) digestion up to 6 h postinfection (hpi). However, transcription of the immediate early (IE) genes ICP0 and ICP4 was significantly upregulated at 3 h postinfection. Also, these genes were found to be less protected from MNase digestion and, therefore, less associated with nucleosomes. These results suggest that Asf1a plays a role in regulating IE genes by assembling chromatin onto histone-free viral DNA by 3 h postinfection.
单纯疱疹病毒（HSV）是一种大型 DNA 病毒，其特征是能够在外周神经系统的神经元中形成潜伏感染。虽然组蛋白存在于小型 DNA 病毒（乳多空病毒）的衣壳中，但在大型 HSV 的衣壳中却没有发现。然而，在进入感染细胞的细胞核后，HSV 基因组在感染的早期阶段开始与核小体结合。相比之下，在感染后期，新复制的病毒 DNA似乎不会与核小体结合，这表明组蛋白是特异性地沉积在输入的病毒 DNA 上。组蛋白从病毒基因组上沉积和去除的机制尚不清楚。最近，参与核小体组装和拆卸的组蛋白伴侣已被鉴定出来。人类抗沉默因子 1（Asf1）就是这样一种因子，它在细胞系统中参与核小体的组装和拆卸。在这项研究中，我们研究了用小干扰 RNA（siRNA）敲低 Asf1a 对 HeLa 细胞中 HSV 感染的影响。发现病毒复制和生长都减少了。此外，在感染后 6 小时内，病毒 DNA 明显较少受到微球菌核酸酶（MNase）的消化。然而，在感染后 3 小时，早期（IE）基因 ICP0 和 ICP4 的转录显著上调。此外，这些基因也被发现较少受到 MNase 消化的保护，因此与核小体的结合也较少。这些结果表明，Asf1a 在感染后 3 小时通过将染色质组装到无组蛋白的病毒 DNA 上，从而在调节 IE 基因方面发挥作用。
