Figure 1. Northern blot showing the induction profile of an inserted reporter gene. Increasing concentrations of tetracycline used for 24 h prior to harvest demonstrates an increased steady‐state amount of reporter gene mRNA (upper panel, lanes 2–8) compared to endogenous GAPDH mRNA levels (lower panel, lanes 2–8). Note that, in this case, endogenous mRNA of similar size can be detected in noninduced cells (lane 1).

Figure 2. Example of an application showing analysis of the splicing products from two integrated CMV promoter‐driven, tetracycline‐inducible, two exon HIV‐1 env expression cassettes. (a) Schematic drawing of the reporter constructs. The cell lines contain similar reporter genes with a single intron, originating from HIV‐1, either with wild‐type 5′ splice site (Wild‐type) or a point mutation in the splice site (5′SS mut). The probe used for the Northern blot in panel (b) is indicated below. CMV‐Tet, tetracycline‐controlled CMV promoter; RRE, Rev response element; (b) Northern blot showing reporter gene expression of two different HEK293 cell lines upon 24 h tetracycline induction of transcription. The cell lines contain the reporter genes indicated in panel (a), including the 5′SS mutant (lanes 1 and 2) or a wild‐type splice donor (lanes 3 and 4). Unspliced and spliced RNAs are indicated to the right (note that the steady‐state RNA level from the splicing‐defective mutant is very low due to a severe transcription defect [ 6]).