[Construction of an infectious retroviral vector for the expression of eucaryotic genes].

We describe here an infectious eucaryotic expression vector derived from Moloney Murine Leukemia (Mo-MuLV) provirus and recombined in plasmid pBR 322, for the expression of eucaryotic genes. Upstream of the cloning sites lie the 5' LTR and 700 bp of the gag sequences containing the splicing and encapsidation signals. Downstream of the cloning sites are situated the env gene and the 3' LTR containing the polyadenylation signal. So as to test the potential use of this vector, Herpes Simplex TK gene and E. Coli NeoR genes were cloned in the same transcriptional polarity as the viral LTRs. When DNA from the recombinant plasmid was transfected into mouse, rat, or human cell cultures, high yields of TK+ or NeoR colonies were obtained. Recombinant plasmids constructed with TK or NeoR genes in the opposite polarity failed to produce drug resistant colonies. Cotransfection with DNA of the Mo-MuLV competent helper provirus led to the rescue of chimeric virus capable of transmitting drug resistance.