Expression of intron VII–spliced and –unspliced mRNAs for EPOR in cell lines transfected with EPOR cDNA with (int7 cDNA) and without (-int cDNA) the intron VII sequence. Transfection was performed using the Lipofectamine reagent. Total RNA was prepared 24 hours after the transfection procedure was terminated. RT-PCR was performed using the primer set of sense-2 and antisense-2. Because the number of cycles was reduced, endogenous mRNA is not demonstrated even in the hematopoietic cells. Since the cDNA used for transfection could directly be a template for PCR to generate a product with the same size as that generated by mRNA, RT-negative reaction mixture was always used as a negative control (see lanes d and e in A and d to f in C). All steps were performed in duplicate. Figures shown are results obtained using COS 7 (A), NIH3T3 (B), HEL (C), and Jurkat (D) cells. The size marker used was BMVI (Boehringer-Mannheim). Among cells transfected with cDNA containing intron VII, EPOR-T mRNA is much more abundant than EPOR-F mRNA in COS 7 and NIH3T3 cells, whereas the ratio of EPOR-T mRNA to EPOR-F mRNA is about the same in hematopoietic cells.