DNA target site sequences and base-pairing interactions for EcI5 introns retargeted to insert at different sites in the E. coli lacZ gene. The retargeted EcI5 introns (targetrons) are denoted by a number that corresponds to the nucleotide position 5′ to the intron-insertion site in the target gene's coding sequence, followed by “a” or “s” indicating antisense or sense strand, respectively. DNA target sequences in the lacZ gene are shown from positions −26 to +10 from the intron-insertion site, with nucleotide residues that match those in the wild-type (WT) EcI5 target site highlighted in gray. The arrow indicates the intron-insertion site. Log-odds scores determined using the computer algorithm described in the text are indicated to the right, along with the targeting frequency determined by plating on LB agar containing X-gal and counting blue and white colonies. Targeting frequencies were determined for targetrons having 5- or 6-bp EBS1/IBS1 interactions. The values are mean±standard deviation for three determinations. (−) not determined; (n.d.) not detectable.
