POLIOVIRUS NEUROVIRULENCE CORRELATES WITH THE PRESENCE OF A CRYPTIC AUG UPSTREAM OF THE INITIATOR CODON

Poliovirus mutants with extended ( > 150-nt) deletions in the 5'-untra nslated region between the internal ribosome entry site and the initia tor codon have been selected previously (Pilipenko et al., Cell 68, 11 9-131, 1992; Gmyl et al., J. Virol. 67, 6309-6316, 1993). These deleti ons were transferred into the genome of a mouse-pathogenic poliovirus strain and found to be strongly attenuating. The deletions can be cons idered as covering three structural elements, a stem-loop (domain E) w ith a conserved cryptic AUG and two spacers, upstream and downstream o f it. In an attempt to identify putative essential determinants of neu rovirulence in these individual structural elements, appropriate mutan ts were engineered, The results demonstrated that neither of the above elements is essential for neurovirulence. The results strongly sugges ted that the presence of a cryptic AUG in the oligopyrimidine/AUG tand em followed, at a sufficient distance, by the initiator codon was nece ssary to ensure the neurovirulent phenotype of our constructs. On the other hand, the attenuated phenotype appeared to correlate with the oc currence of the initiator AUG as a moiety of the oligopyrimidine/AUG t andem. Possible mechanisms underlying these effects are discussed. Ide ntification of the cryptic AUG as an essential determinant for neurovi rulence provides a rational basis for the design of genetically stable attenuated poliovirus variants. (C) 1996 Academic Press, Inc.