Infectious positive- and negative-strand transcript RNAs from bacteriophage Q beta cDNA clones.

Plasmids containing full-length cDNA copies of the Q beta RNA phage genome and flanking T7 promoters were constructed. Positive-strand Q beta RNA, generated by in vitro transcription of these plasmids with T7 RNA polymerase, was infectious to Escherichia coli spheroplasts. The Q beta replicase gene from the cloned DNA was subcloned and expressed in E. coli cells by means of a thermoinducible plasmid. Full-length, negative-strand Q beta transcripts were infectious when transfected into spheroplasts containing the induced replicase gene.