Protects and provides long-distance movement to viral RNA. Self associates and binds viral RNA and fibrillarin to form filamentous ribonucleoproteins (RNPs) protected from RNase. ORF3 protein actually fulfills functions that are usually provided by capsid protein, which is absent from umbraviruses' genome. Homooligomer. Interacts with host FIB2; this interaction, is required for ORF3 protein transiting through host Cajal body and nucleolus, relocalization of fibrillarin to the cytoplasm, and in presence of viral RNA, leads to the formation of stable RNPs. Passes through Cajal bodies to the nucleolus and exits back into the cytoplasm (PubMed:17410203). This journey is absolutely required for the formation of viral RNPs particles (PubMed:17410203). In the cytoplasm, forms in large cytoplasmic inclusions (PubMed:12584328).