Inner capsid (core) component. Displays NTPase, RNA 5'-triphosphatase (RTPase) and RNA helicase activities and probably participates in transcription of the viral genome. Helicase activity might be involved in unwinding or reannealing dsRNA during RNA synthesis. RTPase enzymatic activity represents the first step in RNA capping, which yields a 5'-diphosphorylated plus-strand RNA (By similarity). ATP + H2O = ADP + H(+) + phosphate Interacts with protein mu-NS; in viral inclusions. Found in the inner capsid (120 copies). Belongs to the orthoreovirus lambda-1 protein family.