Fig. 1.

Genetic structure of PVS-RIPO. The genome of the life-attenuated vaccine strain poliovirus type 1 (Sabin) was modified by exchange of the internal ribosomal entry site (IRES; gray box) with that of HRV2 (Gromeier et al., 1996). EcoRI (5′ terminal IRES) and SacI (5′ open reading frame, introduced through silent mutagenesis) restriction endonuclease sites were used for insertion of the foreign sequences into the PV1(S) genome. The main proteolytic cleavage products of the single polyprotein are indicated; viral gene products 2B, 2C, and 2BC are released through proteolytic cleavage of P2.