A screen for gene regulators encoded by Kaposi’s sarcoma-associated herpesvirus uncovers a novel role for the ORF42 protein in regulating the production of cellular and viral proteins

The tight control of viral and host gene expression is critical to the replication of herpesviruses, including the gamma-herpesvirus Kaposis sarcoma-associated herpesvirus (KSHV). While some of the KSHV proteins that contribute to viral and host gene regulation are known, it is clear that there are additional uncharacterized contributing viral factors. Identifying these proteins and their role in gene regulation is important to determine the mechanistic underpinnings of the complex replication cycle of KSHV. Through a reporter-based screen, we have identified several new potential KSHV-encoded gene regulators, including the previously uncharacterized protein ORF42, which we find stimulates global protein production upon overexpression. We have generated an ORF42-null virus, which revealed that ORF42 is required for wild-type levels of virus production. Moreover, global protein synthesis and the accumulation of viral proteins are reduced in infected cells in the absence of ORF42, suggesting that ORF42 regulates protein synthesis during infection. A comparison of the effects of ORF42 on the levels of RNA and protein suggests that ORF42 acts post-transcriptionally to control protein levels. In addition to gene regulation, ORF42 may have other functions in virion formation, as it is found in viral particles, which is consistent with the described roles of the ORF42 homologs in alpha- and beta-herpesviruses.\n\nImportanceKaposis sarcoma-associated herpesvirus (KSHV) causes Kaposis sarcoma, an AIDS-associated malignancy that remains one of the leading causes of cancer deaths in sub-Saharan Africa. Replication of the virus is important for tumor formation and inhibition of viral replication may be used for treatment. The correct levels and temporal expression of viral and host genes during KSHV replication are key to viral replication, but the mechanisms that control this regulation remain enigmatic. Here we identify several new KSHV proteins involved in viral and cellular gene regulation and characterize the previously unstudied KSHV ORF42 protein in regulation of viral and host protein levels and efficient formation of viral progeny.