Nucleic acid amplification with dna-dependent rna polymerase activity of rna replicases

Abstract

The present invention entails methods, and kits for carrying them out, based on the discovery that an RNA replicase, such as Q&bgr; replicase, has DNA-dependent RNA polymerase (“DDRP”) activity with nucleic acid segments, including DNA segments and DNA:RNA chimeric segments, which comprise a 2′-deoxyribonucleotide or an analog thereof and which have sequences of RNAs that are autocatalytically replicatable by the replicase. The discovery of this DDRP activity provides methods of the invention for nucleic acid amplification wherein a nucleic acid, with a DNA segment with the sequence of an RNA that is autocatalytically replicatable by an RNA replicase, is provided as a substrate for the replicase. The replicase catalyzes synthesis, from the DNA segment, of the RNA, which the replicase then autocatalytically replicates. The invention entails use of the amplification methods in detecting nucleic acid analytes, as in nucleic acid probe hybridization assays. Such assays of the invention include those wherein a nucleic acid analyte is hybridized with one or more nucleic acid probes, which include or are processed to generate a DNA segment which is amplifiable through production from the segment, catalyzed by the DDRP activity of an RNA replicase, of an autocatalytically replicatable RNA, which is autocatalytically replicated to provide an abundance of readily detectable reporter molecules. The invention permits replacement of an RNA, that is autocatalytically replicatable with an RNA replicase and employed as a reporter or label in prior art assays, such as nucleic acid probe hybridization assays or immunoassays, with a nucleic acid comprising a DNA segment with the same base sequence as the RNA. The invention also includes the methods of the invention with Mn , Co , or Zn in the solutions in which the DDRP activity occurs.