FIG. 3.

Regulation of GFP expression by using DOX-inducible siRNA. (A) HeLa cells carrying a single copy of a lentivirus vector expressing GFP from the EF-1α promoter (HeLa-GFP) were transduced with a control lentivirus vector (LV-TH) or with vectors producing a GFP-specific siRNA in a constitutive (LV-Hsi) or regulated (LV-THsi) manner, with or without LV-tTR-KRAB (lacking the internal ribosome entry site-dsRed cassette) and/or DOX as indicated. A truncated form of NGFR (ΔNGFR) served as an internal reporter in the siRNA vectors. (B) Conditional expression of the internal marker gene. HeLa-GFP cells dually transduced with LV-THsi/GFP and LV-tTR-KRAB were maintained in the presence or absence of DOX before FACS analysis with a monoclonal antibody specific for the extracellular domain of NGFR.