May be involved in the regulation of cell differentiation. Promotes intracellular multiplication of tobamoviruses, probably being a component of the replication complex. Homodimer. Constituent of tobamovirus replication complex (By similarity). Additional isoforms may exist. Expressed in rosette leaves. Slightly reduced efficiency of intracellular multiplication of tobamoviruses (e.g. crucifer strain TMV-Cg), characterized by a reduced amplification of TMV-related RNAs. Belongs to the tetraspanin (TM4SF) family.