text: Methods
  Therefore, we developed a reciprocal system of a full-length HIV packaging cell line and a shortened HI-viral shuttle vector. The Tat-deficient packaging construct is stably integrated in a VSVG-pseudotyped cell line and transactivated by the shuttle vector by expression of TATGFP from a heterologous promoter which also indicates positive cells. Expression of the HI-viral structure proteins is driven by a natural 5' LTR promoter and a 3' polyadenylation signal, whereas the envelope expression out of the shuttle vector is achieved by an IRES. This system of two vectors is tightly controllable and bypasses the problem of limited packaging capacity into HIV-1 virions.
  
entities.text: ['full-length HIV packaging cell line']
entities.type: Cell
entities.entity_id: PMC-2767981-sec-02_T1
entities.text: ['VSVG-pseudotyped cell line']
entities.type: Cell
entities.entity_id: PMC-2767981-sec-02_T2
entities.text: ['cells']
entities.type: Cell
entities.entity_id: PMC-2767981-sec-02_T3
entities.text: ['envelope']
entities.type: Cellular_component
entities.entity_id: PMC-2767981-sec-02_T4