Rr. Breaker et Gf. Joyce, EMERGENCE OF A REPLICATING SPECIES FROM AN IN-VITRO RNA EVOLUTION REACTION, Proceedings of the National Academy of Sciences of the United Statesof America, 91(13), 1994, pp. 6093-6097
The technique of self-sustained sequence replication allows isothermal
amplification of DNA and RNA molecules in vitro. This method relief o
n the activities of a reverse transcriptase and a DNA-dependent RNA po
lymerase to amplify specific nucleic acid sequences. We have modified
this protocol to allow selective amplification of RNAs that catalyze a
particular chemical reaction. During an in vitro RNA evolution experi
ment employing this modified system, a unique class of ''selfish'' RNA
s emerged and replicated to the exclusion of the intended RNAs. Member
s of this class of selfish molecules, termed RNA Z, amplify efficientl
y despite their inability to catalyze the target chemical reaction. Th
eir amplification requires the action of both reverse transcriptase an
d RNA polymerase and involves the synthesis of both DNA and RNA replic
ation intermediates. The proposed amplification mechanism for RNA Z in
volves the formation of a DNA hairpin that functions as a template for
transcription by RNA polymerase, This arrangement links the two stran
ds of the DNA, resulting in the production of RNA transcripts that con
tain an embedded RNA polymerase promoter sequence.