FIG. 3.

Reconstruction experiment to determine sensitivities of PCRs. Strain LA DNA was mixed together with CT DNA to obtain the indicated concentration of BHV-1 DNA per microgram of CT DNA. Southern blot hybridization of the gE1/2 and gEN1/2 PCR products with the internal probe (derived from the gEN1/2 PCR product) radioactively labelled with ³²P was performed. The sizes of the specific amplification products are indicated. (A) Exposure of X-ray film for 30 min. A total of 10 fg of strain LA DNA per μg of CT DNA is detectable after gE-1–gE-2 PCR (upper part), and at least 10 ag of viral DNA per μg of CT DNA is detectable after nested gEN-1–gEN-2 PCR (lower part). (B) An increase in the time of exposure to X-ray film to 2 h demonstrates a 10-fold increase in the limit of detection.