Inducible retroviral vectors regulated by lac repressor in mammalian cells.

We have developed lac repressor-regulated retroviral expression vectors that are induced by beta-galactosides upon stable transduction in mammalian cells. These vectors, derived from a Moloney-virus-based vector LNCX, contain an internal Rous sarcoma virus (RSV) or cytomegalovirus (CMV) promoter, coupled with 2 to 4 lac operator sequences and placed in anti orientation relative to the retroviral long terminal repeat (LTR). Three different vectors were tested in stably infected mass populations of mouse and human cells expressing the lac repressor, in parallel with the constitutively expressed LNCX vector. The highest expression levels from these vectors ranged from 1-4% to 25-33% of the LNCX level, and the induction by beta-galactosides ranged from 6-11-fold to 29-54-fold. These vectors should be suitable for studies requiring efficient gene transfer and regulated expression in mass populations of stably transduced mammalian cells.