The article discusses the Paramecium bursaria Chlorella virus 1 (PBCV1) that causes the host transcription to off. It presents the study conducted by Zhou and his colleagues, which proposes that the factors that underlie this mechanism are packaged in the PBCV1 virion. VSET was discovered through immunoprecipitation and mass spectrometry. It reveals that expression of vSET was sufficient to repress gene transcription, which confirmed that vSET methylates H3K27 within a living organism.