Figure 1.

(A) Schematic representation of pSFV1-I-CAT and pSFV1-CAT constructs. Only the SFV recombinant regions are shown. The SP6 promoter is indicated by an open arrow. The subgenomic SFV promoter and the SV40 promoter are indicated with solid arrows. SFVnsp1–4 represents the coding region of the SFV nonstructural proteins 1 to 4. The recombinant retroviral genome (R-U5-ψ⁺-NEO-SV40-IN-CAT-pA-U3-R) is inserted downstream of the subgenomic SFV promoter. The SV40 early promoter is used to initiate the transcription of the CAT gene. A chimeric intron (IN) is inserted between the SV40 promoter and the CAT gene in pSFV1-I-CAT. In pSFV1-CAT, this intron has been removed. An internal, SV40-derived poly(A) signal (pA) is present downstream of the CAT gene in both constructs. (B) Titers of retrovirus vector preparations. RNA was prepared from plasmid constructs and used for vector production in BHK-21 cells. Media were harvested and titrated for neo^R-transduction competent retrovirus vectors on NIH 3T3 cells. The titers shown are the number of neomycin-resistant colonies obtained from 1 ml of medium. The maps are not drawn to scale.