Primer-dimers from previously generated reactions demonstrate a strong inhibitory effect on legitimate target amplification of MLV Gag region. a) The negative control reactions (water and PCR reagents but no DNA) from the PSMA PCR and MLV Gag PCR were diluted as shown. Both sets of dilutions were used to contaminate a PCR for MLV Gag. The MLV Gag PCR used Titanium Taq Polymerase and buffer and the PSMA PCR used NEB Taq Polymerase and buffer, with both PCRs being non-UNG containing. b) A negative control reaction (water and PCR reagents but no DNA) from the MLV Gag PCR was diluted 1 × 10-7. This PCR, which used non-UNG containing Titanium Taq Polymerase and buffer, was used to contaminate a subsequent MLV Gag PCR. The MLV-plasmid was used in decreasing copy number, as indicated.