The packaging signal has a conserved RNA secondary structure featuring four AGC/GUAAU internal loop motifs[6]. Within the viral genome the packaging signal is located in the nonstructural protein 15 (nsp15) and encodes a polypeptide which is found on the surface of the nsp15 protein[7]. Deleting the packaging signal or introducing mutations that disrupt its secondary structure but not the encoded peptide lead to the loss of packaging specificity.