Figure 1.

Expression of the Tetrahymena group I intron in E. coli. (A) Diagram of pMALEC-IVS. An EcoRI-HindIII fragment containing the Tetrahymena intron (IVS) was ligated into pMAL-c2 (12). The 5′ exon contains 8 bp and the 3′ exon contains 29 bp of rRNA sequence. Sequences of 5′ and 3′ splice sites (SS) and the IGS are shown. (B) Induction of intron RNA vs. time after addition of IPTG. Fraction of primer extension product corresponding to spliced intron (closed) and pre-RNA (open) are plotted vs. time after addition of IPTG to cultures. The primer anneals to the 5′ end of the intron and distinguishes whether the 5′ splice site has been cleaved. As almost no pMALEC-IVS intron–3′ exon intermediate can be detected on Northern blots, this product corresponds closely to the amount of linear intron in the cell.