Cloning of RNA molecules in vitro.

A method for RNA amplification in an immobilized medium is described. The medium contains a complete set of nucleotide substrates and purified Q beta replicase, an enzyme capable of exponentially amplifying RNAs under isothermal conditions. RNA amplification in the immobilized medium results in the formation of separate 'colonies', each comprising the progeny of a single RNA molecule (a clone). The colonies were visualized by staining with ethidium bromide, by utilizing radioactive substrates, and by hybridization with sequence-specific labeled probes. The number and identity of the RNA colonies corresponded to that of the RNAs seeded. When a mixture of different RNA species was seeded, these species were found in different colonies. Possible implementations of this technique include a search for recombinant RNAs, very sensitive nucleic acid diagnostics, and gene cloning in vitro.