FIG. 1.

Transduction of human and sheep cells by vectors bearing chimeric ENTV/JSRV Env proteins. At the top is the expression cassette used to express the Env proteins. The arrow indicates the transcription start site, and the abbreviations are the following: LTR, retroviral long terminal repeat promoter; SD, splice donor; SA, splice acceptor; SP, endoplasmic reticulum signal peptide; SU, Env surface subunit; TM, Env transmembrane subunit; and SV40 pA, simian virus 40 polyadenylation signal. Hybrid Env proteins (open boxes represent ENTV Env, hatched boxes represent JSRV Env) were made using the indicated restriction enzyme sites, and the relationship of these sites and the SP/SU and SU/TM cleavage sites are shown. LAPSN vectors bearing the indicated Env proteins were made by transient transfection as described in Materials and Methods. SSF and HT-1080 cells, seeded at 10⁵ per well (diameter, 3.5 cm) of 6-well plates, were exposed to the vectors 1 day later and were stained to detect AP⁺ foci 2 days after vector exposure. Values are averages of two experiments with duplicate determinations in each experiment. Data are from reference 3.