Towards development of an in vitro translation test for poliovirus neurovirulence

We showed previously, using a cell-free system from Krebs-2 cells, that the genomes of the Sabin type 1 and 3 poliovaccine strains are poorly translated compared to RNAs of their neurovirulent progenitors. Here we show that similar or even greater differences in translation efficiencies of RNAs from attenuated and virulent poliovirus strains are exhibited by extracts prepared from HeLa cells. In addition, RNA of the Sabin type 2 vaccine is shown to be less efficient in translation that RNA of the revertant strain, 117, isolated from a case of vaccine associated paralytic poliomyelitis. Sabin-derived strains of all three serotypes selected for growth in the human gut were typically characterized by the increased translation efficiency of their genomes. The observed augmentation in translation efficiency correlated well with the occurrence of point mutations in the putative 5' cis-acting element controlling translation and neurovirulence. The mutations were shown to restore the base pairings, disrupted in the Sabin strains, in the predicted secondary structure of the control element. The results demonstrate the usefulness of the cell-free translation assay for differentiation of closely related poliovirus strains on the basis of their neurovirulence.