FUNCTIONAL AND GENETIC PLASTICITIES OF THE POLIOVIRUS GENOME - QUASI-INFECTIOUS RNAS MODIFIED IN THE 5'-UNTRANSLATED REGION YIELD A VARIETYOF PSEUDOREVERTANTS

Poliovirus RNA species with nucleotides 564 to 571 deleted or with a s econdary structure domain (positions 564 to 629) replaced by a shorter irregular oligonucleotide have been engineered previously; these RNAs have been considered quasi-infectious (yielding a single late reverta nt plaque) and dead, respectively (E. Pilipenko, A. Gmyl, Y. Svitkin, S. Maslova, A. Sinyakov, and V. Agol, Cell 68:119-131, 1992). By using large amounts of these RNAs for transfections, revertant clones with a great variety of genetic changes (point mutations, insertions of for eign sequences, short or extended deletions) were isolated. The patter n of these changes supported the notion that an appropriately spaced o ligopyrimidine-AUG tandem is important for efficient poliovirus RNA tr anslation. Structural features within and around this tandem modulated the initiation efficiency. The functional and genetic plasticities of the poliovirus genome are briefly discussed.