Fig. 4. Southern blot analysis of RT–PCR products corresponding to exogenous and endogenous SC35 mRNAs expressed in HeLa cell clones. One-tenth of the PCR products corresponding to SC35 exogenous (A) or endogenous (B) mRNAs expressed in different HeLa cell clones were analyzed with the indicated probes. The structure and size of the transcripts corresponding to the PCR products are indicated and the positions of the PCR primers (arrowheads) and probes (short bold line) are shown. For each probe, the percentage of the hybridization signal corresponding to each PCR product was determined by PhosphorImager analysis for four independent clones of the same series and the mean values are indicated on the right. RT–PCR analysis of the GAPDH mRNA was performed to normalize for RNA amounts used in the RT step. (A) RT–PCR analysis of exogenous SC35 mRNAs from HeLa cell clones stably transfected with coding (E11 and E23) or non-coding (F3 and F10) SC35 genomic sequences and incubated for 48 h in the presence of Dox. (B) RT–PCR analysis of endogenous SC35 mRNAs expressed in HeLa cell clones stably transfected with coding cDNA (A), non-coding cDNA (C), coding genomic (E) or non-coding genomic (F) SC35 sequences prior to or 96 h after Dox induction.