Translocation activity of C-terminal domain of pestivirus Erns and ribotoxin L3 loop

The pestivirus envelope glycoprotein E-rns has RNase activity and therefore was suspected to enter cells to cleave RNA. The protein contains an RNase domain with a C-terminal extension, which shows homology with a membrane-active peptide. The modular architecture and the C-terminal homology suggested that the C terminus could be responsible for the presumed translocation. Peptides corresponding to the C-terminal domain of E-rns and also the homologous L3 loop of ribotoxin II were indeed able to translocate across the eukaryotic cell membrane and were targeted to the nucleoli. The entire E-rns protein was also able to translocate into the cell. Furthermore, other labeled proteins and even active enzymes could be transported inside the cell when they were attached to the C-terminal E-rns peptide. Translocation was energy-independent and not mediated by a protein receptor. The peptides showed no specificity for cell type or species.