Genome-wide screen reveals UL49 is an essential vPIC subunit that transcribes late Human Cytomegalovirus genes

More than half the world's population is infected with Human Cytomegalovirus (HCMV), increasing risks for the immuno-compromised, and causing significant congenital birth defects. The HCMV genome encodes >170 proteins; many that remain uncharacterised, which restricts development opportunities for new antivirals. In this study, a molecular assay was developed to conduct a genome-wide HCMV screen to identify genes that function during late stages of infection. Saliently, loss of UL49 completely abolished production of infectious virions. During infection, UL49 displayed leaky late expression kinetics and nuclear localization. Functionally, UL49 is as an essential subunit of the viral pre-initiation complex (vPIC), enhancing transcription of late viral genes containing non-canonical TATT motif promoters. RNA-seq revealed the full repertoire of vPIC-regulated genes, including transcripts coding for capsid subunits, envelope glycoproteins and egress-associated tegument proteins. Therefore, UL49 together with other vPIC subunits, serve as fundamental HCMV effectors that govern successful completion of the replication cycle. Comparative gene expression profiling analysis of RNA-seq data for HCMV AD169 WT and vPIC subunit KO infected MRC5 fibroblasts at 72 HPI.