VIROLOGY 147,243-252 (1985) The Genomes of Attenuated and Virulent Poliovirus Strains Differ in Their in Vitro Translation Efficiencies’ YURI V. SVITKIN, SVETLANA V. MASLOVA, AND VADIM I. AGOL2 Institute of Poliomyelitis and Viral Encephalitides, USSR Academy of Medical Sciences, Moscow Region 142782, and Moscou State University, Moscow 119899, USSR Received April 8, 1985; accepted July 18, 1985 In mRNA-dependent extracts of Krebs-2 cells, RNAs from attenuated strains of poliovirus type 1 and type 3 exhibited diminished template activity as compared to RNAs from the respective virulent counterparts. This defect appeared to be due to the impaired initiation of viral polyprotein synthesis as evidenced by a relatively low level of accumulation of polypeptide la (which corresponds to an NHa-terminal region of the polyprotein) in samples programmed with RNAs from attenuated strains. In reticulocyte lysates, where poliovirus RNA is translated predominantly from abnormal (internal) sites [Dorner et al. (1984) J. Viral. 50,5075141, this difference in the overall template activity of the attenuated and virulent poliovirus genomes was less pronounced, but the correct initiation (as judged by polypeptide la accumulation) was again more efficient on RNAs from virulent strains. It is suggested that template deficiency is a factor contributing to the attenuated phenotype of poliovirus strains studied. A possible involvement of nucleotide sequences located far upstream from the initiator codon in the control of translation of poliovirus genome is briefly discussed. 0 1985 Academic PEW., h. INTRODUCTION Virulence of polioviruses varies so widely that some strains cause epidemics in non- immune human populations, while others are successfully used as live vaccines. Sev- eral approaches are currently being at- tempted to elucidate the molecular basis of this difference. Important information comes from comparisons of the RNA nu- cleotide sequences of virulent and atten- uated poliovirus strains (Kitamura et al, 1981; Racaniello and Baltimore, 1981a; Nomoto et aL, 1982; Stanway et ab, 1983a, 1984; Toyoda et ak, 1984) but due to a mul- titude of mutations involved, this approach has not yet led to the identification of the genome segment(s) responsible for the at- tenuated or virulent phenotype of appro- priate strains. Assaying neurovirulence of recombinants between attenuated and vir- ulent parents, coupled to the determination 1 Reported in part at the 16th FEBS Meeting (Mos- cow, June 25-30,1984). ‘To whom requests for reprints should be ad- dressed. of the structure of the recombinant ge- nomes, makes location of such segments feasible. Using this technique, it has re- cently been shown that it is the 5’ half of the viral genome that bears major deter- minants of poliovirus neurovirulence (Ago1 et aL, 1983, 1984, 1985a, 198513). Although the resolving power of such an analysis is in principle high, practical limitations are serious enough; thus far only a rather rough mapping of the relevant determi- nants could be accomplished. One may hope that some of these limitations will be over- come by the advent of infectious poliovirus cDNA clones (cf. Racaniello and Baltimore, 1981b; Semler et aL, 1984). Another way to approach the problem of molecular mechanisms of poliovirus atten- uation is a comparison of specific functional properties of related strains differing in the level of their pathogenicity. Several steps of the reproductive cycle of neurovirulent (Mahoney) and attenuated (LSc 2ab) strains of poliovirus type 1 were analyzed and numerous differences were found (cf. Priess and Eggers, 1968; Garfinkle and 243 0042-6822/85 $3.00 Copyright 0 1985 by Academic Press, Inc. All rights of reproduction in any form reserved.