Fig. 5. RT–PCR detects spliced product of the nuclear-expressed bI4 intron in the presence of CP1-containing LeuRS fragments. The RT–PCR products were produced and analyzed on a 1% agarose gel as described previously (Rho and Martinis, 2000). DNA markers are in lane 1. A diffuse band near the gel bottom is excess primer. RT–PCR primers target the B4 exon and MS2–RNA 3′ fusion. A band at ∼1.7 kb represents unspliced RNA that includes flanking exons and the intron. A band at 346 bp indicates ligated B4–B5 exons. Lane 2 shows amplified DNA from three-hybrid cells that only express the bI4 intron. A control in lane 3 shows RT–PCR-amplified RNA from three-hybrid cells that contained the bI4 intron and IleRS CP1 domain. Lane 4 represents an IRE and IRP control. Lanes 5–10 contain samples isolated from three-hybrid cells that expressed bI4 intron from p3MbI4R in the presence of the LeuRS fragments that contained CP1.