Efficient templates for Qβ replicase are formed by recombination from heterologous sequences

A very efficient replicase template has been isolated from the products of spontaneous RNA synthesis in an in vitro Qβ replicase reaction that was incubated in the absence of added RNA. This template was named RQ135 RNA because it is 135 nucleotides in length. Its sequence consists entirely of segments that are homologous to ribosomal 23 S RNA and the phage λ origin of replication. The sequence segments are unrelated to the sequence of Qβ bacteriophage genomic RNA. Nonetheless, this natural recombinant is replicated in vitro at a rate equal to the most efficient of the known Qβ RNA variants. Apparently, the structural properties that ensure recognition of an RNA template by Qβ replicase are not confined to viral RNA, but can appear as a result of recombination among other RNAs that usually occur in cells.