Functional formation of domain V of the poliovirus noncoding region: Significance of unpaired bases

Previously we have shown that polioviruses with mutations that disrupt the predicted secondary structure of the 5' noncoding region of domain V are te mperature sensitive for growth. Non-temperature-sensitive revertant viruses had mutations that re-formed secondary structure by a direct back mutation of changes in the opposite strand. We mutated unpaired regions and selecte d revertants of viruses with single base deletions, where no obvious back m utation was available in order to gain information on secondary structure. Results indicated that conservation of length of a three base loop between two double-stranded stems was essential for a functional domain V to form. The requirement for the unpaired "hinge" base at 484 which is implicated in the attenuation of Sabin 2 was also confirmed. Results also underline the necessity for functional folding over local secondary structure stability. (C) 2001 Academic Press.