FIGURE 1.

Retroviral life cycle and retroviral vector particle transduction. (Left) Retroviruses may enter a target cell by membrane fusion. The capsid core is released to the cytoplasm. Reverse transcription copies the viral genomic RNA (black lines) to a linear double stranded cDNA. Integrase binds the ends of the viral cDNA forming a pre-integration complex (PIC). Lentiviral PICs are able to cross an intact nuclear membrane while all other retroviruses require cellular division to access the host genome. Integrase mediates the stable integration of the vDNA (black) to the host genome (blue) generating the provirus. Host transcription machinery generates viral mRNAs and genomic RNA. Progeny viral particles assemble and are released from the plasma membrane. Following budding from the cell, viral enzyme protease cleaves the polyproteins to generate a mature infectious virus particle. (Right) Retroviral vector particles recapitulate the early steps of the retroviral life cycle. Viral RNA and cDNA depicted in red. However, they do not encode viral proteins. Only the protein of interest is expressed.