What is the fine-grained topic of the following text: KSHV open reading frame 50 (ORF50), a homolog of the Epstein-Barr virus immediate-early gene product RTA, activates early and late gene transcription in the KSHV lytic cycle, and its expression is closely correlated with KSHV-related diseases. Only return the topic.
KSHV ORF50 gene product RTA and its role in KSHV lytic cycle and related diseases.