Kaposi’s sarcoma-associated herpesvirus (KSHV) is one of the few oncogenic human viruses known to date. Its large genome encodes more than 85 proteins and includes both unique viral proteins as well as proteins conserved amongst herpesviruses. KSHV ORF20 is a member of the herpesviral core UL24 family, but the function of ORF20 and its role in the viral life cycle is not well understood. ORF20 encodes three largely uncharacterized isoforms, which we found were localized predominantly in the nuclei and nucleoli. Quantitative affinity purification coupled to mass spectrometry (q-AP-MS) identified numerous specific interacting partners of ORF20, including ribosomal proteins and the interferon-stimulated gene product (ISG) oligoadenylate synthetase-like protein (OASL). Both endogenous and transiently transfected OASL co-immunoprecipitated with ORF20, and this interaction was conserved among all ORF20 isoforms and multiple ORF20 homologs of the UL24 family in other herpesviruses. Characterization of OASL interacting partners by q-AP-MS identified a very similar interactome to that of ORF20. Both ORF20 and OASL copurified with 40S and 60S ribosomal subunits, and when they were co-expressed, they associated with polysomes. Although ORF20 did not have a global effect on translation, ORF20 enhanced RIG-I induced expression of endogenous OASL in an IRF3-dependent but IFNAR-independent manner. OASL has been characterized as an ISG with antiviral activity against some viruses, but its role for gammaherpesviruses was unknown. We show that OASL and ORF20 mRNA expression were induced early after reactivation of latently infected HuARLT-rKSHV.219 cells. Intriguingly, we found that OASL enhanced infection of KSHV. During infection with a KSHV ORF20stop mutant, however, OASL-dependent enhancement of infectivity was lost. Our data have characterized the interaction of ORF20 with OASL and suggest ORF20 usurps the function of OASL to benefit KSHV infection.

卡波济氏肉瘤相关疱疹病毒（KSHV）是迄今为止已知的少数致癌人类病毒之一。它的大型基因组编码超过85种蛋白质，包括独特的病毒蛋白质以及疱疹病毒中保守的蛋白质。KSHV ORF20是疱疹病毒核心UL24家族的成员，但是对ORF20的功能及其在病毒生命周期中的作用还知之甚少。ORF20编码三种很大程度上未表征的同工型，我们发现它们主要位于细胞核和核仁中。定量亲和纯化与质谱联用（q-AP-MS）鉴定出ORF20的许多特异性相互作用伙伴，包括核糖体蛋白和干扰素刺激的基因产物（ISG）寡腺苷酸合成酶样蛋白（OASL）。内源性和瞬时转染的OASL与ORF20共同免疫沉淀，在其他疱疹病毒中，所有ORF20同工型和UL24家族的多个ORF20同系物之间的相互作用均得到保守。通过q-AP-MS对OASL相互作用伙伴进行表征，发现与ORF20的相互作用组非常相似。ORF20和OASL均与40S和60S核糖体亚基共纯化，当它们被共表达时，它们与多核糖体相关。尽管ORF20对翻译没有全局影响，但ORF20以IRF3依赖性但与IFNAR无关的方式增强了RIG-1诱导的内源性OASL的表达。OASL被描述为具有对某些病毒具有抗病毒活性的ISG，但它对伽玛疱疹病毒的作用尚不清楚。我们显示，OASL和ORF20 mRNA表达在潜伏感染的HuARLT-rKSHV.219细胞重新激活后早期被诱导。有趣的是 我们发现OASL增强了KSHV的感染。但是，在用KSHV ORF20stop突变体感染期间，失去了OASL依赖性的感染力增强。我们的数据已表征了ORF20与OASL的相互作用，并暗示ORF20破坏了OASL的功能以有益于KSHV感染。