Chinchar V G, Yu W
Department of Microbiology, University of Mississippi Medical Center, Jackson 39216.
Virology. 1992 Feb;186(2):435-43. doi: 10.1016/0042-6822(92)90008-d.
Treatment of purified frog virus 3 (FV3) with nonionic detergent and high salt released an endoribonucleolytic activity and confirmed earlier findings of a virion-associated endonuclease. This observation, coupled with evidence implicating host and viral message destabilization in herpesvirus and poxvirus biogenesis, raised the question of what role, if any, mRNA degradation plays in FV3 replication. To answer this question, Northern analyses of mock- and virus-infected cells were performed using probes for representative host and viral messages. These studies demonstrated that the steady state level of host messages progressively declined during the course of productive FV3 infection, whereas the steady state level of viral messages was not affected. To determine whether the decline in the steady state level of host mRNA was due to virus-induced degradation or to normal turnover coupled to virus-mediated transcriptional shut-off, actin mRNA levels were examined in mock- and virus-infected cells in the presence and absence of actinomycin D. Under these conditions, actin mRNA levels declined more quickly in actinomycin D-treated, virus-infected cells, than in mock-infected cells incubated in the presence of actinomycin D suggesting that the decline in the steady state level of actin mRNA was due to degradation. However, although it appears as if host message degradation is responsible for virus-mediated translational shut-off, the ability of heat-inactivated FV3 to block cellular translation without destabilizing cellular messages indicates that message degradation is not required for translational inhibition. As noted above, the degradation of early FV3 messages was not involved in controlling the transition from early to late gene expression. Furthermore, the presence of abundant, but nontranslated, early messages late in infection, coupled with the inefficient translation of late messages in vitro supported earlier suggestions that FV3 gene expression is controlled, at least in part, at the translational level. Taken together, these results suggest that FV3 regulates gene expression in a unique manner and may be a good model to examine the mechanics of translational control.
用非离子去污剂和高盐处理纯化的青蛙病毒3（FV3）释放出一种核糖核酸内切酶活性，证实了先前关于病毒体相关核酸内切酶的发现。这一观察结果，再加上有证据表明在疱疹病毒和痘病毒生物发生过程中宿主和病毒信息的不稳定，引发了一个问题，即mRNA降解在FV3复制中起什么作用（如果有作用的话）。为了回答这个问题，使用针对代表性宿主和病毒信息的探针，对模拟感染和病毒感染的细胞进行了Northern分析。这些研究表明，在FV3生产性感染过程中，宿主信息的稳态水平逐渐下降，而病毒信息的稳态水平不受影响。为了确定宿主mRNA稳态水平的下降是由于病毒诱导的降解还是与病毒介导的转录关闭相关的正常周转，在有和没有放线菌素D的情况下，检测了模拟感染和病毒感染细胞中肌动蛋白mRNA的水平。在这些条件下，经放线菌素D处理的病毒感染细胞中肌动蛋白mRNA水平的下降比在有放线菌素D存在下培养的模拟感染细胞中更快，这表明肌动蛋白mRNA稳态水平的下降是由于降解。然而，尽管似乎宿主信息降解是病毒介导的翻译关闭的原因，但热灭活的FV3在不破坏细胞信息的情况下阻断细胞翻译的能力表明，信息降解不是翻译抑制所必需的。如上所述，FV3早期信息的降解不参与控制从早期到晚期基因表达的转变。此外，感染后期存在大量但未翻译的早期信息，再加上晚期信息在体外翻译效率低下，支持了早期的观点，即FV3基因表达至少部分在翻译水平上受到控制。综上所述，这些结果表明FV3以独特的方式调节基因表达，可能是研究翻译控制机制的一个良好模型。
