Retrovirus Resource Site
Detailed review of retroviral gene expression and practical recommendations.
Self-inactivating Retroviral Vectors
Self-inactivating retroviral vectors, also called Q Vectors, are engineered so that transcription of the target gene can only be driven by an internal promoter once the expression cassette is integrated into the genome. These vectors are constructed by deleting the enhancer and/or the promoter in the U3 region of the 3' LTR. During reverse transcription, a circular intermediate is formed that transfers the deletion to the 5' LTR of the proviral DNA. The deletion abolishes any transcriptional activity driven by the LTR so that no full-length vector RNA is produced in transduced cells. Following a single round of replication, the changes are copied into both 5' and 3' LTRs resulting in inactive provirus.
Self-inactivating retroviral vectors usually include an internal promoter that remains active in the cell/tissue of interest. In that way, expression of a gene of interest can be driven by the internal promoter.
Self-inactivating retroviral vectors have several major advantages. The self-inactivation of the retroviral vector minimizes the risk that RCRs (Replication Competent Retrovirus) will emerge. It also reduces the likelihood that cellular coding sequences located adjacent to the vector integration site will be aberrantly expressed, either due to the promoter activity of the 3' LTR or through an enhancer effect. These vectors are a significant development in gene therapy research where a particular concern is preventing incidental activation of an endogenous oncogene. Finally, a potential transcriptional interference between the LTR and the internal promoter (used for expression in tissue/cells of interest) driving the transgene is prevented by the Self Inactivating (SIN) vector design.
1. Martin et al., (2000) BioTechniques 28:702–708.