FIG. 3.

Differentiation between cloned virus and parental VR-2332 strain. A BstZ17I restriction site was introduced in the full-length cDNA clone of VR-2332 to allow discrimination between cloned virus (tagged with the BstZ17I site) and parental virus (lacks a BstZ17I site). RNA was extracted from lysates of cells infected with either the cloned virus or the parental VR-2332 isolate, and a 990-bp fragment was amplified by RT-PCR as described in Materials and Methods. The amplicons were digested with BstZ17I and analyzed on a 2.5% agarose gel. The presence of a BstZ17I restriction site resulted in fragments of 762 bp and 228 bp. As expected, the restriction site was found in the cloned virus but not in the parental VR-2332 virus isolate.