Historically, ribosomes were viewed as unchanged homogeneous macromolecular machines with no regulatory capacity for mRNA translation. An emerging concept is that heterogeneity of ribosomal composition exists, exerting a regulatory function or specificity in translational control. This is supported by recent discoveries identifying compositionally distinct specialised ribosomes that actively regulate mRNA translation. Viruses lack their own translational machinery and impose high translational demands on the host during replication. We explore the possibility that KSHV manipulates ribosome biogenesis producing specialised ribosomes which preferentially translate viral transcripts. Quantitative proteomic analysis identified changes in the stoichiometry and composition of precursor ribosomal complexes during the switch from latent to lytic replication. We demonstrate the enhanced association of ribosomal biogenesis factors BUD23 and NOC4L, and the KSHV ORF11 protein, with small ribosomal subunit precursor complexes during lytic replication. BUD23 depletion resulted in significantly reduced viral gene expression, culminating in dramatic reduction of infectious virion production. Ribosome profiling demonstrated BUD23 is essential for reduced association of ribosomes with KSHV uORFs in late lytic genes, required for the efficient translation of the downstream coding sequence. Results provide mechanistic insights into KSHV-mediated manipulation of cellular ribosome composition inducing a population of specialised ribosomes facilitating efficient translation of viral mRNAs.

Historically, ribosomes have been viewed as unchanged homogeneous macromolecular machines with no intrinsic regulatory capacity for mRNA translation. However, an emerging concept is that heterogeneity of ribosomal composition exists, which can exert a regulatory function or specificity in translational control. This is supported by recent discoveries identifying compositionally distinct specialised ribosomes that actively regulate mRNA translation. Viruses lack their own translational machinery and impose a high translational demand on the host cell during replication. Here we explore the possibility that Kaposi sarcoma associated herpesvirus can manipulate host ribosome biogenesis during infection to produce specialised ribosomes which preferentially translate viral transcripts. Quantitative proteomic analysis has identified changes in the stoichiometry and composition of precursor ribosomal complexes during the switch from latent to lytic KSHV replication. Intriguingly, we demonstrate the enhanced association of ribosomal biogenesis factors BUD23 and NOC4L, and a previously uncharacterised KSHV lytic protein, ORF11, with small ribosomal subunit precursor complexes during lytic KSHV infection. Notably, BUD23 depletion resulted in significantly reduced viral gene expression and progression through the lytic cascade, culminating in a dramatic reduction of infectious virion production. Importantly, ribosome profiling demonstrated that BUD23 is essential for the reduced association of ribosomes with KSHV uORFs in late lytic genes, required for the efficient translation of the main open reading frame. Together our results provide new mechanistic insights into KSHV-mediated manipulation of cellular ribosome composition inducing a population of specialised ribosomes to facilitate efficient translation of viral mRNAs.