Identification of a new element for RNA replication within the internal ribosome entry site of poliovirus RNA

Several mutants of the Mahoney strain of poliovirus type 1 have been genera ted by introducing mutations into the stem-loop II (SLII) structure within the internal ribosomal entry site (IRES). Four of these mutants (SLII-1, -4 , -5 and -6 mutants) have been characterized previously and are host-range mutants that replicate well in human HeLa cells but not in mouse cells. Two deletion mutants, SLII-2 and SLII-3, were non-viable, even in HeLa cells. It is now reported that SLII-2 was defective in genome RNA synthesis and vi ral protein synthesis, while SLII-3 was defective only in viral protein syn thesis. These results indicate that the SLII region contains a cis-element for RNA replication as well as for IRES-dependent translation and that thes e two functions lie at the same sites within the SLII region. The host cell ular factors that interacted with wildtype SLII and mutant SLII-2 and SLII- 3 RNAs were different, suggesting that different host-factor binding regula tes expression of mutant phenotypes.