Elimination of primer-dimer artifacts with rhPCR. A 242 bp HCV amplicon known to produce primer-dimer artifacts was used to compare the specificity of unmodified control (U) and "rDDDDx" blocked-cleavable (B) primers. M = marker lane (bp, double-stranded). PCR assays were run without (left) or with (right) RNase H2 and included reactions with primers alone, primers plus the synthetic HCV target, or primers and the synthetic HCV target with high complexity rat cDNA. Reaction products were separated by non-denaturing PAGE, fluorescently stained, and visualized by UV excitation.