Fig. 5. Combined results obtained in 6 PCR assays (groups A-F) using various primer sets reacted with DNA from stealth virus-1-infected MRC-5 cells (left lane in each group); SCMV-infected cells (middle lane in each group); or uninfected cells (right lane in each group). The primer sets used in group A and in group B were based on the stealth virus-1 plasmids 15-5-4 and 15-5-2, respectively (Martin et al., 1994). Two primer sets were used in each of the groups C through F. In group C, one set was designed to amplify a 587-base pair region within the origin of lytic replication (oriLyt) gene of SCMV. The other set was designed to amplify a 416-base pair region of the 'bent DNA' gene of SCMV. In group D, the primer set giving a product with both stealth virus-1 and SCMV was designed to amplify a region within the stealth virus-1-derived plasmid 3B647. This plasmid contains sequences showing partial homology to the UL44 gene of HCMV. The primer set which gave a product with SCMV, but not stealth virus-1, was designed to amplify a 565-base pair region within the (CA) dinucleotide repeat gene of SCMV. In group E, the primer set giving a 219-base pair product with both stealth virus-1 and SCMV was designed to amplify a region within the stealth virus-1-derived plasmid 3B642. This primer set also generated a weak band of approximately 900 base pairs with both stealth virus-1 and SCMV. The 3B642 plasmid contains sequences showing partial homology to the UL48 gene of HCMV. In group E, the primer set giving a product with stealth virus-1, but not with SCMV, was designed to amplify a region within the stealth virus-1-derived plasmid 3B660. This plasmid contains sequences showing partial homology to the UL87 gene of HCMV. In group F, the primer set giving a 1200-base pair product with SCMV, but not with stealth virus-1, was designed to amplify a region within the MIE gene of SCMV. The actual sequences of the primers used are given in Table 1. DNA size markers from 50 to 1000 bases (marker XI) from Boehringer Mannheim, IN, and HIND III cut lambda phage were run in lanes 1 and 20, respectively.