Dissecting the role of RNA-binding proteins in early herpes simplex virus 1 transcription using acute protein depletion

Herpes simplex virus 1 (HSV-1) infects about 50-80% of the entire human population and persists in the neurons of affected individuals. A fraction of affected individuals suffer from recurrent cold sores caused by reactivating virus, in rare but severe cases the virus can cause encephalitis. During lytic infection, the virus relies on host factors such as RNA polymerase II and accessory proteins involved in transcription to express its genes and ensure successful replication. In general, RNA molecules in cells are bound by RNA-binding proteins (RBPs) during their entire lifecycle. Importantly, RBPs are increasingly described to also regulate transcription, an aspect long time outside the scope of investigations, especially during viral infections. Here, we examined the impact of five nuclear proteins (FUBP1, SLBP, SFPQ, SPT5 and SAF-B) with known RNA-binding activities on HSV-1 transcription. Additionally, we evaluated their importance for human adenovirus C5 (HAdV) growth to assess whether these host factors are specific to HSV-1 infections or might have broader relevance for the general transcription of dsDNA viruses. We show that the transcriptional elongation factor SPT5 coded by SUPT5H accumulates on HSV-1 genomes early during the infection and is required for the transcription of the immediate-early gene UL54. Its depletion affects also HAdV replication, indicating a general role in transcription of viruses that depend on the host transcriptional machinery. In contrast, depletion of the transcriptional repressor and paraspeckle protein SFPQ reduces UL54 RNA levels in HSV-1 infection, but does not cause significant changes in HAdV growth. Since SFPQ does not co-localize with HSV-1 genomes, this suggests a function not directly associated to viral DNA.