Minor inner capsid (core) component. Displays NTPase and RNA 5'-triphosphatase (RTPase) activities. ATP is the preferred substrate for hydrolysis. May function as a cofactor of polymerase lambda-3. Associates with microtubules and plays a role in the formation, structural organization and morphology of viral inclusions, where the assembly of cores and the replication of viral RNA occur. Together with mu-NS, recruits the other core proteins to these inclusions (By similarity). Interacts with protein mu-NS; in viral inclusions. Interacts with polymerase lambda-3; this interaction stimulates the ATPase activity of mu-2 (By similarity). Found in the inner capsid (12 copies). Belongs to the orthoreovirus mu-2 protein family.