Poliovirus requires a precise 5 ' end for efficient positive-strand RNA synthesis

Poliovirus infectious RNA can be synthesized in vitro using phage DNA-depen dent RNA-polymerases. These synthetic transcripts contain several extra nuc leotides at the 5' end, which are deleted during replication to generate au thentic viral genomes. We removed those 5'-end extra nucleotides utilizing a hammerhead ribozyme to produce transcripts with accurate 5' ends. These t ranscripts replicate substantially more rapidly in cell culture, demonstrat ing no lag before replication; they also replicate more efficiently in Xeno pus laevis oocytes and in in vitro translation-replication cell extracts. I n both systems, an exact 5' end is necessary for synthesis of positive-stra nd RNA but not negative-strand RNA.