Exponential Amplification of Recombinant- RNA Hybridization Probes

Abstract

We have synthesized recombinant RNA molecules that function both as hybridization probes and as templates for exponential amplification by Qβ replicase. Each recombinant consists of a sequence specific for the protozoan parasite, Plasmodium falciparum, embedded within the sequence of MDV-1 RNA, which is a natural template for Qβ replicase. The probe sequence was inserted within a hairpin loop that occurs on the exterior of MDV-1 RNA. The recombinant RNAs hybridize specifically to complementary DNA, despite topological constraints on the probe domain, are replicated at the same rate as MDV-1 RNA, despite their additional length, and are able to serve as templates for the synthesis of a large number of RNA copies. A Qβ replicase reaction initiated with only 0.14 femtograms of recombinant RNA (1,000 molecules) can produce 129 nanograms of recombinant RNA product in 30 minutes. This represents a one-billion fold amplification. Our results demonstrate the feasibility of employing exponentially replicatable RNAs in bioassays, where they would serve the dual role of specific probe and amplifiable reporter.