FIG 1.

Transcription-mediated amplification (TMA). The single-stranded RNA target is bound by a cDNA primer engineered to contain a T7 viral RNA polymerase promoter sequence (red box). Reverse transcriptase (RT) extends the DNA primer to form an RNA-cDNA duplex, and the RNA template strand is degraded by RNase H activity. A second primer anneals to the single-stranded cDNA (black) and is extended by RT, which incorporates the T7 promoter into the double-stranded DNA sequence. T7 RNA polymerase recognizes the incorporated T7 promoter sequence and synthesizes 100 to 1,000 copies of single-strand RNA amplicon (green). These amplicons serve both as a target for detection probes and as a single-stranded template for subsequent rounds of amplification using the non-T7 primer to initiate cDNA synthesis by RT.