Interruption of env gene expression depending on the length of the SV40 early region used for the polyA signal.

In order to invent a screening system to check in vivo gene function and the efficiency of gene transfer mediated by a retroviral vector system, we established a novel packaging cell, PacNIH/A8, based on the neuropathogenic retrovirus A8-V. To construct the expression vector, pA8(Psi-), which expresses the genes gag, pol and env derived from A8-V, the SV40 early region was used for the polyadenylation signal (polyA signal). When a 0.85 kbp fragment in the SV40 early region was employed for the expression vector (pA8(Psi-)beta), env expression was abolished. This abolition was rescued by shortening the SV40 early region to 0.14 kbp (pA8(Psi-)delta). The NHI3T3 cells transfected with pA8(Psi-)delta showed expressions of both env and gag genes.