Retroviral Delivery of the Ecdysone-Regulatable Gene Expression System

We describe a set of Moloney Murine Leukemia Virus (MoMLV)‐based replication‐defective retroviral vectors for delivery of the ecdysone‐inducible system into mammalian cells. The vector pFB‐ERV contains a tricistronic CMV expression cassette from which the ecdysone receptor proteins RXR and VgEcR are expressed, with the neo‐resistance marker expressed as the third open reading frame (ORF). The inducible vector pCFB‐EGSH contains an ecdysone‐inducible expression cassette inserted between the viral LTRs in the antisense orientation relative to that for the viral promoter. Potential interference from the proviral 5′ LTR is obviated due to a SIN deletion in the 3′ LTR. When used together, induction ratios of over 1000‐fold were achieved in NIH3T3 cells using firefly luciferase as a reporter.